93 lines
3.4 KiB
Diff
93 lines
3.4 KiB
Diff
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From 63dbbc5c52f9823f86270f32fce20d1e91cdf484 Mon Sep 17 00:00:00 2001
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From: Sergio Durigan Junior <sergiodj@sergiodj.net>
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Date: Wed, 1 Nov 2023 18:15:23 -0400
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Subject: [PATCH] sysdeps: sem_open: Clear O_CREAT when semaphore file is
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expected to exist [BZ #30789]
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When invoking sem_open with O_CREAT as one of its flags, we'll end up
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in the second part of sem_open's "if ((oflag & O_CREAT) == 0 || (oflag
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& O_EXCL) == 0)", which means that we don't expect the semaphore file
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to exist.
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In that part, open_flags is initialized as "O_RDWR | O_CREAT | O_EXCL
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| O_CLOEXEC" and there's an attempt to open(2) the file, which will
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likely fail because it won't exist. After that first (expected)
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failure, some cleanup is done and we go back to the label "try_again",
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which lives in the first part of the aforementioned "if".
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The problem is that, in that part of the code, we expect the semaphore
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file to exist, and as such O_CREAT (this time the flag we pass to
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open(2)) needs to be cleaned from open_flags, otherwise we'll see
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another failure (this time unexpected) when trying to open the file,
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which will lead the call to sem_open to fail as well.
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This can cause very strange bugs, especially with OpenMPI, which makes
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extensive use of semaphores.
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Fix the bug by simplifying the logic when choosing open(2) flags and
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making sure O_CREAT is not set when the semaphore file is expected to
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exist.
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A regression test for this issue would require a complex and cpu time
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consuming logic, since to trigger the wrong code path is not
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straightforward due the racy condition. There is a somewhat reliable
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reproducer in the bug, but it requires using OpenMPI.
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This resolves BZ #30789.
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See also: https://bugs.launchpad.net/ubuntu/+source/h5py/+bug/2031912
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Signed-off-by: Sergio Durigan Junior <sergiodj@sergiodj.net>
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Co-Authored-By: Simon Chopin <simon.chopin@canonical.com>
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Co-Authored-By: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
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Fixes: 533deafbdf189f5fbb280c28562dd43ace2f4b0f ("Use O_CLOEXEC in more places (BZ #15722)")
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(cherry picked from commit f957f47df75b9fab995754011491edebc6feb147)
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---
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NEWS | 2 ++
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sysdeps/pthread/sem_open.c | 10 ++++------
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2 files changed, 6 insertions(+), 6 deletions(-)
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diff --git a/sysdeps/pthread/sem_open.c b/sysdeps/pthread/sem_open.c
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index e5db929d20..0e331a7445 100644
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--- a/sysdeps/pthread/sem_open.c
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+++ b/sysdeps/pthread/sem_open.c
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@@ -32,11 +32,12 @@
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# define __unlink unlink
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#endif
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+#define SEM_OPEN_FLAGS (O_RDWR | O_NOFOLLOW | O_CLOEXEC)
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+
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sem_t *
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__sem_open (const char *name, int oflag, ...)
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{
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int fd;
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- int open_flags;
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sem_t *result;
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/* Check that shared futexes are supported. */
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@@ -65,10 +66,8 @@ __sem_open (const char *name, int oflag, ...)
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/* If the semaphore object has to exist simply open it. */
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if ((oflag & O_CREAT) == 0 || (oflag & O_EXCL) == 0)
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{
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- open_flags = O_RDWR | O_NOFOLLOW | O_CLOEXEC;
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- open_flags |= (oflag & ~(O_CREAT|O_ACCMODE));
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try_again:
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- fd = __open (dirname.name, open_flags);
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+ fd = __open (dirname.name, (oflag & O_EXCL) | SEM_OPEN_FLAGS);
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if (fd == -1)
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{
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@@ -135,8 +134,7 @@ __sem_open (const char *name, int oflag, ...)
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}
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/* Open the file. Make sure we do not overwrite anything. */
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- open_flags = O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC;
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- fd = __open (tmpfname, open_flags, mode);
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+ fd = __open (tmpfname, O_CREAT | O_EXCL | SEM_OPEN_FLAGS, mode);
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if (fd == -1)
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{
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if (errno == EEXIST)
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--
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2.43.0
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