From patchwork Thu Nov 7 22:10:10 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Adhemerval Zanella (Code Review)" X-Patchwork-Id: 1191446 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org (client-ip=209.132.180.131; helo=sourceware.org; envelope-from=libc-alpha-return-106797-incoming=patchwork.ozlabs.org@sourceware.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=gnutoolchain-gerrit.osci.io Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; secure) header.d=sourceware.org header.i=@sourceware.org header.b="MGBZZHvI"; dkim-atps=neutral Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 478Hdq3jhcz9sNH for ; Fri, 8 Nov 2019 09:10:23 +1100 (AEDT) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:date:from:to:subject:in-reply-to:references :reply-to:mime-version:content-transfer-encoding:content-type :message-id; q=dns; s=default; b=kFWt+sHBhDd3SSmidsWb8R00IQRHHsS Ta+zpaVOFqi17a0U8K++8u6dBW/+XCb4HijjRX5CZ+bOrsVOpSUdlPeqcDPnEb0+ pWHa9L6AT3XPyoZQ/XushcVhuf68wCiwXO1kFyWgiH4uylQ3Gb15bOiQ40DjBpa5 x31Ic+FkNPNU= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:date:from:to:subject:in-reply-to:references :reply-to:mime-version:content-transfer-encoding:content-type :message-id; s=default; bh=ZOlSZlbbSoKay8hzmlRzhQQ/u2I=; b=MGBZZ HvInK2A2Fimc3yj1kNJQfeaa6DB1MkaI1o3w4odbBwZqWIuwHlDi9chHGrpQ+U+Y jq91iG2QMIPXeODxx0RAVkrOPF7v/tm5MzrMAZQUZpL42WRus4OHQxWvd8Gc/gxS 0PfFTITWkP7fcNAFJXCTePuaNVS7XDHT0yYWBM= Received: (qmail 21480 invoked by alias); 7 Nov 2019 22:10:17 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 21471 invoked by uid 89); 7 Nov 2019 22:10:17 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-26.9 required=5.0 tests=BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_SHORT autolearn=ham version=3.3.1 spammy= X-HELO: mx1.osci.io X-Gerrit-PatchSet: 4 Date: Thu, 7 Nov 2019 17:10:10 -0500 From: "Sourceware to Gerrit sync (Code Review)" To: Florian Weimer , Carlos O'Donell , libc-alpha@sourceware.org Auto-Submitted: auto-generated X-Gerrit-MessageType: newpatchset Subject: [pushed] login: Acquire write lock early in pututline [BZ #24882] X-Gerrit-Change-Id: I57e31ae30719e609a53505a0924dda101d46372e X-Gerrit-Change-Number: 523 X-Gerrit-ChangeURL: X-Gerrit-Commit: be6b16d975683e6cca57852cd4cfe715b2a9d8b1 In-Reply-To: References: Reply-To: noreply@gnutoolchain-gerrit.osci.io, fweimer@redhat.com, libc-alpha@sourceware.org, carlos@redhat.com MIME-Version: 1.0 Content-Disposition: inline User-Agent: Gerrit/3.0.3-75-g9005159e5d Message-Id: <20191107221010.47E6925B28@gnutoolchain-gerrit.osci.io> The original change was created by Florian Weimer. Change URL: https://gnutoolchain-gerrit.osci.io/r/c/glibc/+/523 ...................................................................... login: Acquire write lock early in pututline [BZ #24882] It has been reported that due to lack of fairness in POSIX file locking, the current reader-to-writer lock upgrade can result in lack of forward progress. Acquiring the write lock directly hopefully avoids this issue if there are only writers. This also fixes bug 24882 due to the cache revalidation in __libc_pututline. Reviewed-by: Carlos O'Donell Change-Id: I57e31ae30719e609a53505a0924dda101d46372e --- M login/Makefile A login/tst-pututxline-cache.c M login/utmp_file.c 3 files changed, 240 insertions(+), 33 deletions(-) diff --git a/login/Makefile b/login/Makefile index 0183db1..6a0182b 100644 --- a/login/Makefile +++ b/login/Makefile @@ -44,7 +44,7 @@ vpath %.c programs tests := tst-utmp tst-utmpx tst-grantpt tst-ptsname tst-getlogin tst-updwtmpx \ - tst-pututxline-lockfail + tst-pututxline-lockfail tst-pututxline-cache # Build the -lutil library with these extra functions. extra-libs := libutil @@ -74,3 +74,4 @@ -$(INSTALL_PROGRAM) -m 4755 -o root $< $@ $(objpfx)tst-pututxline-lockfail: $(shared-thread-library) +$(objpfx)tst-pututxline-cache: $(shared-thread-library) diff --git a/login/tst-pututxline-cache.c b/login/tst-pututxline-cache.c new file mode 100644 index 0000000..3f30dd1 --- /dev/null +++ b/login/tst-pututxline-cache.c @@ -0,0 +1,193 @@ +/* Test case for cache invalidation after concurrent write (bug 24882). + Copyright (C) 2019 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public License as + published by the Free Software Foundation; either version 2.1 of the + License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; see the file COPYING.LIB. If + not, see . */ + +/* This test writes an entry to the utmpx file, reads it (so that it + is cached) in process1, and overwrites the same entry in process2 + with something that does not match the search criteria. At this + point, the cache of the first process is stale, and when process1 + attempts to write a new record which would have gone to the same + place (as indicated by the cache), it needs to realize that it has + to pick a different slot because the old slot is now used for + something else. */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* Set to the path of the utmp file. */ +static char *utmp_file; + +/* Used to synchronize the subprocesses. The barrier itself is + allocated in shared memory. */ +static pthread_barrier_t *barrier; + +/* setutxent with error checking. */ +static void +xsetutxent (void) +{ + errno = 0; + setutxent (); + TEST_COMPARE (errno, 0); +} + +/* getutxent with error checking. */ +static struct utmpx * +xgetutxent (void) +{ + errno = 0; + struct utmpx *result = getutxent (); + if (result == NULL) + FAIL_EXIT1 ("getutxent: %m"); + return result; +} + +static void +put_entry (const char *id, pid_t pid, const char *user, const char *line) +{ + struct utmpx ut = + { + .ut_type = LOGIN_PROCESS, + .ut_pid = pid, + .ut_host = "localhost", + }; + strcpy (ut.ut_id, id); + strncpy (ut.ut_user, user, sizeof (ut.ut_user)); + strncpy (ut.ut_line, line, sizeof (ut.ut_line)); + TEST_VERIFY (pututxline (&ut) != NULL); +} + +/* Use two cooperating subprocesses to avoid issues related to + unlock-on-close semantics of POSIX advisory locks. */ + +static __attribute__ ((noreturn)) void +process1 (void) +{ + TEST_COMPARE (utmpname (utmp_file), 0); + + /* Create an entry. */ + xsetutxent (); + put_entry ("1", 101, "root", "process1"); + + /* Retrieve the entry. This will fill the internal cache. */ + { + errno = 0; + setutxent (); + TEST_COMPARE (errno, 0); + struct utmpx ut = + { + .ut_type = LOGIN_PROCESS, + .ut_line = "process1", + }; + struct utmpx *result = getutxline (&ut); + if (result == NULL) + FAIL_EXIT1 ("getutxline (\"process1\"): %m"); + TEST_COMPARE (result->ut_pid, 101); + } + + /* Signal the other process to overwrite the entry. */ + xpthread_barrier_wait (barrier); + + /* Wait for the other process to complete the write operation. */ + xpthread_barrier_wait (barrier); + + /* Add another entry. Note: This time, there is no setutxent call. */ + put_entry ("1", 103, "root", "process1"); + + _exit (0); +} + +static void +process2 (void *closure) +{ + /* Wait for the first process to write its entry. */ + xpthread_barrier_wait (barrier); + + /* Truncate the file. The glibc interface does not support + re-purposing records, but an external expiration mechanism may + trigger this. */ + TEST_COMPARE (truncate64 (utmp_file, 0), 0); + + /* Write the replacement entry. */ + TEST_COMPARE (utmpname (utmp_file), 0); + xsetutxent (); + put_entry ("2", 102, "user", "process2"); + + /* Signal the other process that the entry has been replaced. */ + xpthread_barrier_wait (barrier); +} + +static int +do_test (void) +{ + xclose (create_temp_file ("tst-tumpx-cache-write-", &utmp_file)); + { + pthread_barrierattr_t attr; + xpthread_barrierattr_init (&attr); + xpthread_barrierattr_setpshared (&attr, PTHREAD_SCOPE_PROCESS); + barrier = support_shared_allocate (sizeof (*barrier)); + xpthread_barrier_init (barrier, &attr, 2); + } + + /* Run both subprocesses in parallel. */ + { + pid_t pid1 = xfork (); + if (pid1 == 0) + process1 (); + support_isolate_in_subprocess (process2, NULL); + int status; + xwaitpid (pid1, &status, 0); + TEST_COMPARE (status, 0); + } + + /* Check that the utmpx database contains the expected records. */ + { + TEST_COMPARE (utmpname (utmp_file), 0); + xsetutxent (); + + struct utmpx *ut = xgetutxent (); + TEST_COMPARE_STRING (ut->ut_id, "2"); + TEST_COMPARE (ut->ut_pid, 102); + TEST_COMPARE_STRING (ut->ut_user, "user"); + TEST_COMPARE_STRING (ut->ut_line, "process2"); + + ut = xgetutxent (); + TEST_COMPARE_STRING (ut->ut_id, "1"); + TEST_COMPARE (ut->ut_pid, 103); + TEST_COMPARE_STRING (ut->ut_user, "root"); + TEST_COMPARE_STRING (ut->ut_line, "process1"); + + if (getutxent () != NULL) + FAIL_EXIT1 ("additional utmpx entry"); + } + + xpthread_barrier_destroy (barrier); + support_shared_free (barrier); + free (utmp_file); + + return 0; +} + +#include diff --git a/login/utmp_file.c b/login/utmp_file.c index e627233..917c4c5 100644 --- a/login/utmp_file.c +++ b/login/utmp_file.c @@ -186,19 +186,11 @@ /* Search for *ID, updating last_entry and file_offset. Return 0 on - success and -1 on failure. If the locking operation failed, write - true to *LOCK_FAILED. */ + success and -1 on failure. Does not perform locking; for that see + internal_getut_r below. */ static int -internal_getut_r (const struct utmp *id, bool *lock_failed) +internal_getut_nolock (const struct utmp *id) { - int result = -1; - - if (try_file_lock (file_fd, F_RDLCK)) - { - *lock_failed = true; - return -1; - } - if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME || id->ut_type == OLD_TIME || id->ut_type == NEW_TIME) { @@ -213,7 +205,7 @@ { __set_errno (ESRCH); file_offset = -1l; - goto unlock_return; + return -1; } file_offset += sizeof (struct utmp); @@ -234,7 +226,7 @@ { __set_errno (ESRCH); file_offset = -1l; - goto unlock_return; + return -1; } file_offset += sizeof (struct utmp); @@ -243,14 +235,25 @@ } } - result = 0; - -unlock_return: - file_unlock (file_fd); - - return result; + return 0; } +/* Search for *ID, updating last_entry and file_offset. Return 0 on + success and -1 on failure. If the locking operation failed, write + true to *LOCK_FAILED. */ +static int +internal_getut_r (const struct utmp *id, bool *lock_failed) +{ + if (try_file_lock (file_fd, F_RDLCK)) + { + *lock_failed = true; + return -1; + } + + int result = internal_getut_nolock (id); + file_unlock (file_fd); + return result; +} /* For implementing this function we don't use the getutent_r function because we can avoid the reposition on every new entry this way. */ @@ -279,7 +282,6 @@ return 0; } - /* For implementing this function we don't use the getutent_r function because we can avoid the reposition on every new entry this way. */ int @@ -336,7 +338,6 @@ return NULL; struct utmp *pbuf; - int found; if (! file_writable) { @@ -358,7 +359,12 @@ file_writable = true; } + /* Exclude other writers before validating the cache. */ + if (try_file_lock (file_fd, F_WRLCK)) + return NULL; + /* Find the correct place to insert the data. */ + bool found = false; if (file_offset > 0 && ((last_entry.ut_type == data->ut_type && (last_entry.ut_type == RUN_LVL @@ -366,23 +372,30 @@ || last_entry.ut_type == OLD_TIME || last_entry.ut_type == NEW_TIME)) || __utmp_equal (&last_entry, data))) - found = 1; - else { - bool lock_failed = false; - found = internal_getut_r (data, &lock_failed); - - if (__builtin_expect (lock_failed, false)) + if (__lseek64 (file_fd, file_offset, SEEK_SET) < 0) { - __set_errno (EAGAIN); + file_unlock (file_fd); return NULL; } + if (__read_nocancel (file_fd, &last_entry, sizeof (last_entry)) + != sizeof (last_entry)) + { + if (__lseek64 (file_fd, file_offset, SEEK_SET) < 0) + { + file_unlock (file_fd); + return NULL; + } + found = false; + } + else + found = __utmp_equal (&last_entry, data); } - if (try_file_lock (file_fd, F_WRLCK)) - return NULL; + if (!found) + found = internal_getut_nolock (data) >= 0; - if (found < 0) + if (!found) { /* We append the next entry. */ file_offset = __lseek64 (file_fd, 0, SEEK_END); @@ -411,7 +424,7 @@ { /* If we appended a new record this is only partially written. Remove it. */ - if (found < 0) + if (!found) (void) __ftruncate64 (file_fd, file_offset); pbuf = NULL; }