[{"id":3680614,"web_url":"http://patchwork.ozlabs.org/comment/3680614/","msgid":"<46833eeb-72b9-4756-b750-6ab54355fe7f@linaro.org>","list_archive_url":null,"date":"2026-04-22T13:04:34","subject":"Re: [PATCH] misc: Optimize getusershell.c","submitter":{"id":66065,"url":"http://patchwork.ozlabs.org/api/people/66065/","name":"Adhemerval Zanella","email":"adhemerval.zanella@linaro.org"},"content":"On 20/04/26 10:05, Rocket Ma wrote:\n> * misc/getusershell.c: Completely rewrite the unit. Only allocate one\n> big buffer to store shell names. Add a missing unit test.\n> \n> The new implementation read the whole file into one buffer, and wipe out\n> every byte but shell names. Later when addressing shell names from first\n> shell, jump to next '\\0' and then jump to next '/'. This could reduce\n> memory footprint and shall improve some performance.\n> \n> Signed-off-by: Rocket Ma \n\nThis has cause CI regressions [1]:\n\n elf-check-localplt.out\n \n Extra PLT reference: libc.so: endusershell\n Extra PLT reference: libc.so: fread\n Extra PLT reference: libc.so: setbuf\n\nThis is due the use of the non-internal function names that generated extra\nPLT calls.\n\n[1] https://www.delorie.com/trybots/32bit/59989/\n\n> ---\n> misc/Makefile | 1 +\n> misc/getusershell.c | 272 +++++++++++++++++++----------------\n> misc/tst-getusershell.c | 75 ++++++++++\n> misc/tst-getusershell.shells | 7 +\n> 4 files changed, 230 insertions(+), 125 deletions(-)\n> create mode 100644 misc/tst-getusershell.c\n> create mode 100644 misc/tst-getusershell.shells\n> \n> diff --git a/misc/Makefile b/misc/Makefile\n> index 4395366d74..31c930ef64 100644\n> --- a/misc/Makefile\n> +++ b/misc/Makefile\n> @@ -245,6 +245,7 @@ tests := \\\n> tst-empty \\\n> tst-error1 \\\n> tst-fdset \\\n> + tst-getusershell \\\n> tst-hsearch \\\n> tst-insremque \\\n> tst-ioctl \\\n> diff --git a/misc/getusershell.c b/misc/getusershell.c\n> index 4221095dca..19394852a4 100644\n> --- a/misc/getusershell.c\n> +++ b/misc/getusershell.c\n> @@ -1,143 +1,165 @@\n> -/*\n> - * Copyright (c) 1985, 1993\n> - *\tThe Regents of the University of California. All rights reserved.\n> - *\n> - * Redistribution and use in source and binary forms, with or without\n> - * modification, are permitted provided that the following conditions\n> - * are met:\n> - * 1. Redistributions of source code must retain the above copyright\n> - * notice, this list of conditions and the following disclaimer.\n> - * 2. Redistributions in binary form must reproduce the above copyright\n> - * notice, this list of conditions and the following disclaimer in the\n> - * documentation and/or other materials provided with the distribution.\n> - * 4. Neither the name of the University nor the names of its contributors\n> - * may be used to endorse or promote products derived from this software\n> - * without specific prior written permission.\n> - *\n> - * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND\n> - * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE\n> - * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE\n> - * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE\n> - * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL\n> - * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS\n> - * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)\n> - * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT\n> - * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY\n> - * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF\n> - * SUCH DAMAGE.\n> - */\n> -\n> -#if defined(LIBC_SCCS) && !defined(lint)\n> -static char sccsid[] = \"@(#)getusershell.c\t8.1 (Berkeley) 6/4/93\";\n> -#endif /* LIBC_SCCS and not lint */\n> -\n> -#include \n> -#include \n> -#include \n> -#include \n> -#include \n> +/* Copyright (C) 2026 The GNU Toolchain Authors.\n> + This file is part of the GNU C Library.\n> +\n> + The GNU C Library is free software; you can redistribute it and/or\n> + modify it under the terms of the GNU Lesser General Public\n> + License as published by the Free Software Foundation; either\n> + version 2.1 of the License, or (at your option) any later version.\n> +\n> + The GNU C Library is distributed in the hope that it will be useful,\n> + but WITHOUT ANY WARRANTY; without even the implied warranty of\n> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n> + Lesser General Public License for more details.\n> +\n> + You should have received a copy of the GNU Lesser General Public\n> + License along with the GNU C Library; if not, see\n> + . */\n> +\n> #include \n> -#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> #include \n> #include \n> +#include \n> +#include \n> \n> -/*\n> - * Local shells should NOT be added here. They should be added in\n> - * /etc/shells.\n> - */\n> -\n> -/* NB: we do not initialize okshells here. The initialization needs\n> - relocations. These interfaces are used so rarely that this is not\n> - justified. Instead explicitly initialize the array when it is\n> - used. */\n> -#if 0\n> -static const char *const okshells[] = { _PATH_BSHELL, _PATH_CSHELL, NULL };\n> -#else\n> -static const char *okshells[3];\n> -#endif\n> -static char **curshell, **shells, *strings;\n> -static char **initshells (void) __THROW;\n> -\n> -/*\n> - * Get a list of shells from _PATH_SHELLS, if it exists.\n> - */\n> -char *\n> -getusershell (void)\n> +#define DEFAULT_SHELLS _PATH_BSHELL \"\\0\" _PATH_CSHELL\n> +\n> +static char *shellbuf;\n> +static char *shellend;\n> +static char *nextshell;\n> +\n> +static char *\n> +address_next_shell (void)\n> {\n> -\tchar *ret;\n> -\n> -\tif (curshell == NULL)\n> -\t\tcurshell = initshells();\n> -\tret = *curshell;\n> -\tif (ret != NULL)\n> -\t\tcurshell++;\n> -\treturn (ret);\n> + char *curshell;\n> + char *next0;\n> +\n> + curshell = nextshell;\n> + if (nextshell == NULL)\n> + return curshell;\n> +\n> + /* init_shells guarantees we have a \\0 at the end */\n> + next0 = memchr (nextshell, '\\0', shellend - nextshell);\n> + if (next0 == NULL)\n> + /* Unexpected, perhaps user modified our buffer? */\n> + nextshell = NULL;\n> + else\n> + nextshell = memchr (next0, '/', shellend - next0);\n> + return curshell;\n> }\n> \n> -void\n> -endusershell (void)\n> +/* Read /etc/shells, strip unnecessary bytes, and setup nextshell */\n> +static void\n> +init_shells (void)\n> {\n> + FILE *fp;\n> + struct __stat64_t64 fstat;\n> + size_t buflen;\n> + char *top;\n> + char *line_start, *line_end;\n> + char *slash, *discard;\n> +\n> + endusershell ();\n> +\n> + if ((fp = fopen (_PATH_SHELLS, \"rce\")) == NULL)\n> + goto default_out;\n> + if ((__fstat64_time64 (fileno (fp), &fstat)) == -1)\n> + goto close_out;\n> + /* Consider if buflen will overflow. */\n> + if (fstat.st_size < 2 || fstat.st_size > PTRDIFF_MAX - 1)\n> + goto close_out;\n> + /* 1 byte for \\n (will be overwritten as \\0). */\n> + buflen = fstat.st_size + 1;\n> + if ((shellbuf = malloc (buflen)) == NULL)\n> + goto close_out;\n> + shellbuf[buflen - 1] = '\\n';\n> + setbuf (fp, NULL);\n> + if ((fread (shellbuf, 1, fstat.st_size, fp)) != fstat.st_size)\n> + goto free_out;\n> +\n> + top = shellbuf + buflen;\n> + line_start = shellbuf;\n> + while ((line_end = memchr (line_start, '\\n', top - line_start)) != NULL)\n> + {\n> + line_end++; /* include \\n */\n> + discard = line_start;\n> +\n> + slash = memchr (line_start, '/', line_end - line_start);\n> + if (slash == NULL)\n> +\tgoto wipe_line;\n> +\n> + discard = memchr (line_start, '#', line_end - line_start);\n> + if (discard != NULL && discard < slash)\n> +\tgoto wipe_line;\n> +\n> + (void) memset (line_start, '\\0', slash - line_start);\n> + discard = slash;\n> + while (discard < line_end && *discard != '#'\n> +\t && !isspace ((unsigned char) *discard))\n> +\tdiscard++;\n> +\n> + wipe_line:\n> + (void) memset (discard, '\\0', line_end - discard);\n> + line_start = line_end;\n> + }\n> +\n> + if ((nextshell = memchr (shellbuf, '/', top - shellbuf)) == NULL)\n> + goto free_out;\n> + shellend = top;\n> + (void) fclose (fp);\n> + return;\n> \n> -\tfree(shells);\n> -\tshells = NULL;\n> -\tfree(strings);\n> -\tstrings = NULL;\n> -\tcurshell = NULL;\n> +free_out:\n> + free (shellbuf);\n> + shellbuf = NULL;\n> +close_out:\n> + (void) fclose (fp);\n> +default_out:\n> + shellbuf = malloc (sizeof (DEFAULT_SHELLS));\n> + if (shellbuf == NULL)\n> + {\n> + /* Can't allocate a buffer to store default shells,\n> +\t use read-only string to avoid unexpected user write.\n> +\t Leave shellbuf as NULL so that it can be freed. */\n> + nextshell = (char *) DEFAULT_SHELLS;\n> + shellend = (char *) DEFAULT_SHELLS + sizeof (DEFAULT_SHELLS);\n> + }\n> + else\n> + {\n> + memcpy (shellbuf, DEFAULT_SHELLS, sizeof (DEFAULT_SHELLS));\n> + nextshell = shellbuf;\n> + shellend = shellbuf + sizeof (DEFAULT_SHELLS);\n> + }\n> +}\n> +\n> +char *\n> +getusershell (void)\n> +{\n> + if (shellend == NULL)\n> + init_shells ();\n> + return address_next_shell ();\n> }\n> \n> void\n> setusershell (void)\n> {\n> -\n> -\tcurshell = initshells();\n> + if (shellend == NULL)\n> + init_shells ();\n> + else if (shellbuf != NULL)\n> + nextshell = memchr (shellbuf, '/', shellend - shellbuf);\n> + else /* shellend != NULL && shellbuf == NULL */\n> + nextshell = (char *) DEFAULT_SHELLS;\n> }\n> \n> -static char **\n> -initshells (void)\n> +void\n> +endusershell (void)\n> {\n> -\tchar **sp, *cp;\n> -\tFILE *fp;\n> -\tstruct __stat64_t64 statb;\n> -\tsize_t flen;\n> -\n> -\tfree(shells);\n> -\tshells = NULL;\n> -\tfree(strings);\n> -\tstrings = NULL;\n> -\tif ((fp = fopen(_PATH_SHELLS, \"rce\")) == NULL)\n> -\t\tgoto init_okshells_noclose;\n> -\tif (__fstat64_time64(fileno(fp), &statb) == -1) {\n> -\tinit_okshells:\n> -\t\t(void)fclose(fp);\n> -\tinit_okshells_noclose:\n> -\t\tokshells[0] = _PATH_BSHELL;\n> -\t\tokshells[1] = _PATH_CSHELL;\n> -\t\treturn (char **) okshells;\n> -\t}\n> -\tif (statb.st_size > ~(size_t)0 / sizeof (char *) * 3)\n> -\t\tgoto init_okshells;\n> -\tflen = statb.st_size + 3;\n> -\tif ((strings = malloc(flen)) == NULL)\n> -\t\tgoto init_okshells;\n> -\tshells = malloc(statb.st_size / 3 * sizeof (char *));\n> -\tif (shells == NULL) {\n> -\t\tfree(strings);\n> -\t\tstrings = NULL;\n> -\t\tgoto init_okshells;\n> -\t}\n> -\tsp = shells;\n> -\tcp = strings;\n> -\twhile (fgets_unlocked(cp, flen - (cp - strings), fp) != NULL) {\n> -\t\twhile (*cp != '#' && *cp != '/' && *cp != '\\0')\n> -\t\t\tcp++;\n> -\t\tif (*cp == '#' || *cp == '\\0' || cp[1] == '\\0')\n> -\t\t\tcontinue;\n> -\t\t*sp++ = cp;\n> -\t\twhile (!isspace(*cp) && *cp != '#' && *cp != '\\0')\n> -\t\t\tcp++;\n> -\t\t*cp++ = '\\0';\n> -\t}\n> -\t*sp = NULL;\n> -\t(void)fclose(fp);\n> -\treturn (shells);\n> + free (shellbuf);\n> + shellbuf = NULL;\n> + shellend = NULL;\n> + nextshell = NULL;\n> }\n> diff --git a/misc/tst-getusershell.c b/misc/tst-getusershell.c\n> new file mode 100644\n> index 0000000000..b2f71804d8\n> --- /dev/null\n> +++ b/misc/tst-getusershell.c\n> @@ -0,0 +1,75 @@\n> +/* Test the getusershell series functions.\n> + Copyright (C) 2026 The GNU Toolchain Authors.\n> + This file is part of the GNU C Library.\n> +\n> + The GNU C Library is free software; you can redistribute it and/or\n> + modify it under the terms of the GNU Lesser General Public\n> + License as published by the Free Software Foundation; either\n> + version 2.1 of the License, or (at your option) any later version.\n> +\n> + The GNU C Library is distributed in the hope that it will be useful,\n> + but WITHOUT ANY WARRANTY; without even the implied warranty of\n> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n> + Lesser General Public License for more details.\n> +\n> + You should have received a copy of the GNU Lesser General Public\n> + License along with the GNU C Library; if not, see\n> + . */\n> +\n> +#include \"support/temp_file.h\"\n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +\n> +static void\n> +test_in_chroot (void *chroot_path)\n> +{\n> + xchroot (chroot_path);\n> +\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/sh\");\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/bash\");\n> + TEST_COMPARE_STRING (getusershell (), \"/usr/bin/zsh\");\n> + TEST_COMPARE_STRING (getusershell (), NULL);\n> + TEST_COMPARE_STRING (getusershell (), NULL);\n> +\n> + setusershell ();\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/sh\");\n> + endusershell ();\n> +\n> + xunlink (\"/etc/shells\");\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/sh\");\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/csh\");\n> + TEST_COMPARE_STRING (getusershell (), NULL);\n> + endusershell ();\n> +}\n> +\n> +static int\n> +do_test (void)\n> +{\n> + support_become_root ();\n> + if (!support_can_chroot ())\n> + return EXIT_UNSUPPORTED;\n> +\n> + char *chroot_dir = support_create_temp_directory(\"tst-getusershell-\");\n> + char *etc = xasprintf(\"%s/etc\", chroot_dir);\n> + add_temp_file(etc);\n> + xmkdir(etc, 0777);\n> + /* Don't add shells to file list as it will be deleted in test. */\n> + char *shells = xasprintf(\"%s/shells\", etc);\n> + support_copy_file(\"tst-getusershell.shells\", shells);\n> +\n> + support_isolate_in_subprocess(test_in_chroot, chroot_dir);\n> +\n> + free(etc);\n> + free(shells);\n> + free(chroot_dir);\n> +\n> + return 0;\n> +}\n> +\n> +#include \n> diff --git a/misc/tst-getusershell.shells b/misc/tst-getusershell.shells\n> new file mode 100644\n> index 0000000000..fcc7675398\n> --- /dev/null\n> +++ b/misc/tst-getusershell.shells\n> @@ -0,0 +1,7 @@\n> +# test hash\n> + # indentation\n> +\n> +/bin/sh\n> +\t/bin/bash # ...\n> +\n> +xx /usr/bin/zsh#...\n> \\ No newline at end of file","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=Rnm5p9MD;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=2620:52:6:3111::32; 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charset=UTF-8","Content-Transfer-Encoding":"7bit","X-BeenThere":"libc-alpha@sourceware.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Libc-alpha mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org"}},{"id":3682013,"web_url":"http://patchwork.ozlabs.org/comment/3682013/","msgid":"<70a7356a-43a5-41d2-af1b-c03a822b7b90@linaro.org>","list_archive_url":null,"date":"2026-04-24T12:39:31","subject":"Re: [PATCH] misc: Optimize getusershell.c","submitter":{"id":66065,"url":"http://patchwork.ozlabs.org/api/people/66065/","name":"Adhemerval Zanella","email":"adhemerval.zanella@linaro.org"},"content":"On 20/04/26 10:05, Rocket Ma wrote:\n> * misc/getusershell.c: Completely rewrite the unit. Only allocate one\n> big buffer to store shell names. Add a missing unit test.\n> \n> The new implementation read the whole file into one buffer, and wipe out\n> every byte but shell names. Later when addressing shell names from first\n> shell, jump to next '\\0' and then jump to next '/'. This could reduce\n> memory footprint and shall improve some performance.\n> \n> Signed-off-by: Rocket Ma \n\nThe patch seems ok, some minor comments (mostly style issues).\n\n> ---\n> misc/Makefile | 1 +\n> misc/getusershell.c | 272 +++++++++++++++++++----------------\n> misc/tst-getusershell.c | 75 ++++++++++\n> misc/tst-getusershell.shells | 7 +\n> 4 files changed, 230 insertions(+), 125 deletions(-)\n> create mode 100644 misc/tst-getusershell.c\n> create mode 100644 misc/tst-getusershell.shells\n> \n> diff --git a/misc/Makefile b/misc/Makefile\n> index 4395366d74..31c930ef64 100644\n> --- a/misc/Makefile\n> +++ b/misc/Makefile\n> @@ -245,6 +245,7 @@ tests := \\\n> tst-empty \\\n> tst-error1 \\\n> tst-fdset \\\n> + tst-getusershell \\\n> tst-hsearch \\\n> tst-insremque \\\n> tst-ioctl \\\n> diff --git a/misc/getusershell.c b/misc/getusershell.c\n> index 4221095dca..19394852a4 100644\n> --- a/misc/getusershell.c\n> +++ b/misc/getusershell.c\n> @@ -1,143 +1,165 @@\n> -/*\n> - * Copyright (c) 1985, 1993\n> - *\tThe Regents of the University of California. All rights reserved.\n> - *\n> - * Redistribution and use in source and binary forms, with or without\n> - * modification, are permitted provided that the following conditions\n> - * are met:\n> - * 1. Redistributions of source code must retain the above copyright\n> - * notice, this list of conditions and the following disclaimer.\n> - * 2. Redistributions in binary form must reproduce the above copyright\n> - * notice, this list of conditions and the following disclaimer in the\n> - * documentation and/or other materials provided with the distribution.\n> - * 4. Neither the name of the University nor the names of its contributors\n> - * may be used to endorse or promote products derived from this software\n> - * without specific prior written permission.\n> - *\n> - * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND\n> - * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE\n> - * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE\n> - * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE\n> - * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL\n> - * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS\n> - * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)\n> - * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT\n> - * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY\n> - * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF\n> - * SUCH DAMAGE.\n> - */\n> -\n> -#if defined(LIBC_SCCS) && !defined(lint)\n> -static char sccsid[] = \"@(#)getusershell.c\t8.1 (Berkeley) 6/4/93\";\n> -#endif /* LIBC_SCCS and not lint */\n> -\n> -#include \n> -#include \n> -#include \n> -#include \n> -#include \n> +/* Copyright (C) 2026 The GNU Toolchain Authors.\n> + This file is part of the GNU C Library.\n> +\n> + The GNU C Library is free software; you can redistribute it and/or\n> + modify it under the terms of the GNU Lesser General Public\n> + License as published by the Free Software Foundation; either\n> + version 2.1 of the License, or (at your option) any later version.\n> +\n> + The GNU C Library is distributed in the hope that it will be useful,\n> + but WITHOUT ANY WARRANTY; without even the implied warranty of\n> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n> + Lesser General Public License for more details.\n> +\n> + You should have received a copy of the GNU Lesser General Public\n> + License along with the GNU C Library; if not, see\n> + . */\n> +\n> #include \n> -#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> #include \n> #include \n> +#include \n> +#include \n> \n> -/*\n> - * Local shells should NOT be added here. They should be added in\n> - * /etc/shells.\n> - */\n> -\n> -/* NB: we do not initialize okshells here. The initialization needs\n> - relocations. These interfaces are used so rarely that this is not\n> - justified. Instead explicitly initialize the array when it is\n> - used. */\n> -#if 0\n> -static const char *const okshells[] = { _PATH_BSHELL, _PATH_CSHELL, NULL };\n> -#else\n> -static const char *okshells[3];\n> -#endif\n> -static char **curshell, **shells, *strings;\n> -static char **initshells (void) __THROW;\n> -\n> -/*\n> - * Get a list of shells from _PATH_SHELLS, if it exists.\n> - */\n> -char *\n> -getusershell (void)\n> +#define DEFAULT_SHELLS _PATH_BSHELL \"\\0\" _PATH_CSHELL\n> +\n> +static char *shellbuf;\n> +static char *shellend;\n> +static char *nextshell;\n> +\n> +static char *\n> +address_next_shell (void)\n> {\n> -\tchar *ret;\n> -\n> -\tif (curshell == NULL)\n> -\t\tcurshell = initshells();\n> -\tret = *curshell;\n> -\tif (ret != NULL)\n> -\t\tcurshell++;\n> -\treturn (ret);\n> + char *curshell;\n> + char *next0;\n> +\n> + curshell = nextshell;\n> + if (nextshell == NULL)\n> + return curshell;\n> +\n> + /* init_shells guarantees we have a \\0 at the end */\n> + next0 = memchr (nextshell, '\\0', shellend - nextshell);\n> + if (next0 == NULL)\n> + /* Unexpected, perhaps user modified our buffer? */\n> + nextshell = NULL;\n\nI don't think should allow users changing the return value, nor we have this\nset in function contract. Maybe an assert would be better here.\n\n> + else\n> + nextshell = memchr (next0, '/', shellend - next0);\n> + return curshell;\n> }\n> \n> -void\n> -endusershell (void)\n> +/* Read /etc/shells, strip unnecessary bytes, and setup nextshell */\n> +static void\n> +init_shells (void)\n> {\n> + FILE *fp;\n> + struct __stat64_t64 fstat;\n> + size_t buflen;\n> + char *top;\n> + char *line_start, *line_end;\n> + char *slash, *discard;\n> +\n> + endusershell ();\n> +\n> + if ((fp = fopen (_PATH_SHELLS, \"rce\")) == NULL)\n> + goto default_out;\n\nWe try to avoid assignment and comparison in the same expression, we\nprefer to:\n\n fp = fopen (_PATH_SHELLS, \"rce\");\n if (fp == NULL)\n ...\n\n> + if ((__fstat64_time64 (fileno (fp), &fstat)) == -1)\n> + goto close_out;\n> + /* Consider if buflen will overflow. */\n> + if (fstat.st_size < 2 || fstat.st_size > PTRDIFF_MAX - 1)\n> + goto close_out;\n> + /* 1 byte for \\n (will be overwritten as \\0). */\n> + buflen = fstat.st_size + 1;\n> + if ((shellbuf = malloc (buflen)) == NULL)\n> + goto close_out;\n> + shellbuf[buflen - 1] = '\\n';\n> + setbuf (fp, NULL);\n> + if ((fread (shellbuf, 1, fstat.st_size, fp)) != fstat.st_size)\n> + goto free_out;\n> +\n> + top = shellbuf + buflen;\n> + line_start = shellbuf;\n> + while ((line_end = memchr (line_start, '\\n', top - line_start)) != NULL)\n> + {\n> + line_end++; /* include \\n */\n> + discard = line_start;\n> +\n> + slash = memchr (line_start, '/', line_end - line_start);\n> + if (slash == NULL)\n> +\tgoto wipe_line;\n> +\n> + discard = memchr (line_start, '#', line_end - line_start);\n> + if (discard != NULL && discard < slash)\n> +\tgoto wipe_line;\n> +\n> + (void) memset (line_start, '\\0', slash - line_start);\n> + discard = slash;\n> + while (discard < line_end && *discard != '#'\n> +\t && !isspace ((unsigned char) *discard))\n> +\tdiscard++;\n> +\n> + wipe_line:\n> + (void) memset (discard, '\\0', line_end - discard);\n> + line_start = line_end;\n> + }\n> +\n> + if ((nextshell = memchr (shellbuf, '/', top - shellbuf)) == NULL)\n> + goto free_out;\n> + shellend = top;\n> + (void) fclose (fp);\n> + return;\n> \n> -\tfree(shells);\n> -\tshells = NULL;\n> -\tfree(strings);\n> -\tstrings = NULL;\n> -\tcurshell = NULL;\n> +free_out:\n> + free (shellbuf);\n> + shellbuf = NULL;\n> +close_out:\n> + (void) fclose (fp);\n> +default_out:\n> + shellbuf = malloc (sizeof (DEFAULT_SHELLS));\n\nThe current implementation already sets and returns read-only strings,\nso the implicit function contract is user are not supposed to write on\nthe getusershell returned values. So I think there is no much gain in\nreturning allocated strings here.\n\n> + if (shellbuf == NULL)\n> + {\n> + /* Can't allocate a buffer to store default shells,\n> +\t use read-only string to avoid unexpected user write.\n> +\t Leave shellbuf as NULL so that it can be freed. */\n> + nextshell = (char *) DEFAULT_SHELLS;\n> + shellend = (char *) DEFAULT_SHELLS + sizeof (DEFAULT_SHELLS);\n> + }\n> + else\n> + {\n> + memcpy (shellbuf, DEFAULT_SHELLS, sizeof (DEFAULT_SHELLS));\n> + nextshell = shellbuf;\n> + shellend = shellbuf + sizeof (DEFAULT_SHELLS);\n> + }\n> +}\n> +\n> +char *\n> +getusershell (void)\n> +{\n> + if (shellend == NULL)\n> + init_shells ();\n> + return address_next_shell ();\n> }\n> \n> void\n> setusershell (void)\n> {\n> -\n> -\tcurshell = initshells();\n> + if (shellend == NULL)\n> + init_shells ();\n> + else if (shellbuf != NULL)\n> + nextshell = memchr (shellbuf, '/', shellend - shellbuf);\n> + else /* shellend != NULL && shellbuf == NULL */\n> + nextshell = (char *) DEFAULT_SHELLS;\n> }\n> \n> -static char **\n> -initshells (void)\n> +void\n> +endusershell (void)\n> {\n> -\tchar **sp, *cp;\n> -\tFILE *fp;\n> -\tstruct __stat64_t64 statb;\n> -\tsize_t flen;\n> -\n> -\tfree(shells);\n> -\tshells = NULL;\n> -\tfree(strings);\n> -\tstrings = NULL;\n> -\tif ((fp = fopen(_PATH_SHELLS, \"rce\")) == NULL)\n> -\t\tgoto init_okshells_noclose;\n> -\tif (__fstat64_time64(fileno(fp), &statb) == -1) {\n> -\tinit_okshells:\n> -\t\t(void)fclose(fp);\n> -\tinit_okshells_noclose:\n> -\t\tokshells[0] = _PATH_BSHELL;\n> -\t\tokshells[1] = _PATH_CSHELL;\n> -\t\treturn (char **) okshells;\n> -\t}\n> -\tif (statb.st_size > ~(size_t)0 / sizeof (char *) * 3)\n> -\t\tgoto init_okshells;\n> -\tflen = statb.st_size + 3;\n> -\tif ((strings = malloc(flen)) == NULL)\n> -\t\tgoto init_okshells;\n> -\tshells = malloc(statb.st_size / 3 * sizeof (char *));\n> -\tif (shells == NULL) {\n> -\t\tfree(strings);\n> -\t\tstrings = NULL;\n> -\t\tgoto init_okshells;\n> -\t}\n> -\tsp = shells;\n> -\tcp = strings;\n> -\twhile (fgets_unlocked(cp, flen - (cp - strings), fp) != NULL) {\n> -\t\twhile (*cp != '#' && *cp != '/' && *cp != '\\0')\n> -\t\t\tcp++;\n> -\t\tif (*cp == '#' || *cp == '\\0' || cp[1] == '\\0')\n> -\t\t\tcontinue;\n> -\t\t*sp++ = cp;\n> -\t\twhile (!isspace(*cp) && *cp != '#' && *cp != '\\0')\n> -\t\t\tcp++;\n> -\t\t*cp++ = '\\0';\n> -\t}\n> -\t*sp = NULL;\n> -\t(void)fclose(fp);\n> -\treturn (shells);\n> + free (shellbuf);\n> + shellbuf = NULL;\n> + shellend = NULL;\n> + nextshell = NULL;\n> }\n> diff --git a/misc/tst-getusershell.c b/misc/tst-getusershell.c\n> new file mode 100644\n> index 0000000000..b2f71804d8\n> --- /dev/null\n> +++ b/misc/tst-getusershell.c\n> @@ -0,0 +1,75 @@\n> +/* Test the getusershell series functions.\n> + Copyright (C) 2026 The GNU Toolchain Authors.\n> + This file is part of the GNU C Library.\n> +\n> + The GNU C Library is free software; you can redistribute it and/or\n> + modify it under the terms of the GNU Lesser General Public\n> + License as published by the Free Software Foundation; either\n> + version 2.1 of the License, or (at your option) any later version.\n> +\n> + The GNU C Library is distributed in the hope that it will be useful,\n> + but WITHOUT ANY WARRANTY; without even the implied warranty of\n> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU\n> + Lesser General Public License for more details.\n> +\n> + You should have received a copy of the GNU Lesser General Public\n> + License along with the GNU C Library; if not, see\n> + . */\n> +\n> +#include \"support/temp_file.h\"\n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +#include \n> +\n> +static void\n> +test_in_chroot (void *chroot_path)\n> +{\n> + xchroot (chroot_path);\n> +\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/sh\");\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/bash\");\n> + TEST_COMPARE_STRING (getusershell (), \"/usr/bin/zsh\");\n> + TEST_COMPARE_STRING (getusershell (), NULL);\n> + TEST_COMPARE_STRING (getusershell (), NULL);\n> +\n> + setusershell ();\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/sh\");\n> + endusershell ();\n> +\n> + xunlink (\"/etc/shells\");\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/sh\");\n> + TEST_COMPARE_STRING (getusershell (), \"/bin/csh\");\n> + TEST_COMPARE_STRING (getusershell (), NULL);\n> + endusershell ();\n> +}\n> +\n> +static int\n> +do_test (void)\n> +{\n> + support_become_root ();\n> + if (!support_can_chroot ())\n> + return EXIT_UNSUPPORTED;\n> +\n> + char *chroot_dir = support_create_temp_directory(\"tst-getusershell-\");\n\nMissing space before '(' here and below.\n\n> + char *etc = xasprintf(\"%s/etc\", chroot_dir);\n> + add_temp_file(etc);\n> + xmkdir(etc, 0777);\n> + /* Don't add shells to file list as it will be deleted in test. */\n> + char *shells = xasprintf(\"%s/shells\", etc);\n> + support_copy_file(\"tst-getusershell.shells\", shells);\n> +\n> + support_isolate_in_subprocess(test_in_chroot, chroot_dir);\n> +\n> + free(etc);\n> + free(shells);\n> + free(chroot_dir);\n> +\n> + return 0;\n> +}\n> +\n> +#include \n> diff --git a/misc/tst-getusershell.shells b/misc/tst-getusershell.shells\n> new file mode 100644\n> index 0000000000..fcc7675398\n> --- /dev/null\n> +++ b/misc/tst-getusershell.shells\n> @@ -0,0 +1,7 @@\n> +# test hash\n> + # indentation\n> +\n> +/bin/sh\n> +\t/bin/bash # ...\n> +\n> +xx /usr/bin/zsh#...\n> \\ No newline at end of file","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=CJ011V+7;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=38.145.34.32; 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