[{"id":3683898,"web_url":"http://patchwork.ozlabs.org/comment/3683898/","msgid":"","list_archive_url":null,"date":"2026-04-29T08:29:32","subject":"Re: [PATCH] libio: Fix race in _IO_new_file_init_internal\n initialization order [BZ #33785]","submitter":{"id":14312,"url":"http://patchwork.ozlabs.org/api/people/14312/","name":"Florian Weimer","email":"fweimer@redhat.com"},"content":"* Shamil Abdulaev:\n\n> _IO_new_file_init_internal linked the new stream into _IO_list_all\n> before setting fp->_fileno to -1. A concurrent thread that walks\n> _IO_list_all (for example via fflush (NULL)) could observe the stream\n> with an uninitialized _fileno before initialization completed.\n>\n> Set _fileno = -1 before _IO_link_in so the stream is fully\n> initialized when it becomes visible in the global list.\n>\n> This is the residual concurrency defect noted at the end of commit\n> b657f72fa3 (\"libio: Fix deadlock between freopen, fflush (NULL) and\n> fclose (bug 24963)\").\n>\n> Add libio/tst-file-init-race exercising concurrent fopen/fclose and\n> fflush (NULL) to detect regressions.\n>\n> Signed-off-by: Shamil Abdulaev \n> ---\n> libio/Makefile | 3 ++\n> libio/fileops.c | 2 +-\n> libio/tst-file-init-race.c | 66 ++++++++++++++++++++++++++++++++++++++\n> 3 files changed, 70 insertions(+), 1 deletion(-)\n> create mode 100644 libio/tst-file-init-race.c\n>\n> diff --git a/libio/Makefile b/libio/Makefile\n> index 93656466df..7e448295e3 100644\n> --- a/libio/Makefile\n> +++ b/libio/Makefile\n> @@ -107,6 +107,7 @@ tests = \\\n> tst-fgetc-after-eof \\\n> tst-fgetwc \\\n> tst-fgetws \\\n> + tst-file-init-race \\\n> tst-fopenloc2 \\\n> tst-fputws \\\n> tst-freopen \\\n> @@ -160,6 +161,8 @@ tests-static += \\\n> \n> $(objpfx)tst-popen-fork: $(shared-thread-library)\n> \n> +$(objpfx)tst-file-init-race: $(shared-thread-library)\n> +\n> tests-internal = tst-vtables tst-vtables-interposed\n> \n> ifeq (yes,$(build-shared))\n> diff --git a/libio/fileops.c b/libio/fileops.c\n> index 8067c0a9cf..9348d7c3a1 100644\n> --- a/libio/fileops.c\n> +++ b/libio/fileops.c\n> @@ -111,8 +111,8 @@ _IO_new_file_init_internal (struct _IO_FILE_plus *fp)\n> fp->file._offset = _IO_pos_BAD;\n> fp->file._flags |= CLOSED_FILEBUF_FLAGS;\n> \n> - _IO_link_in (fp);\n> fp->file._fileno = -1;\n> + _IO_link_in (fp);\n> }\n\nThanks for investigating this and fixing it.\n\nWould you please apply the parallel change to libio/oldfileops.c? It\nlooks like it has the same bug.\n\nFlorian","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 (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=M3IkDXe1;\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; helo=vm01.sourceware.org;\n envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=M3IkDXe1","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; spf=pass smtp.mailfrom=redhat.com","server2.sourceware.org;\n arc=none smtp.remote-ip=170.10.129.124"],"Received":["from vm01.sourceware.org (vm01.sourceware.org\n [IPv6:2620:52:6:3111::32])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g59Tj4Wf0z1yHv\n\tfor ; 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You could perhaps use xfopen/xfclose, but some of us\nprefer not to use error-checking wrappers for functions under test.\n\nThanks,\nFlorian","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 (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=e8tu6j13;\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; helo=vm01.sourceware.org;\n envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=e8tu6j13","sourceware.org; dmarc=pass (p=quarantine dis=none)\n header.from=redhat.com","sourceware.org; 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