Bug#161992: libc6: Unlocking an unlocked and already destroyed mutex on fclose()
Package: libc6
Version: 2.2.5-6.0.1
Severity: normal
Tags: patch
(the version number 6.0.1 is from the privately built package with
this patch already applied.)
There is a bug in the fclose logic regarding the locking behaviour. It
currently works this way:
1. lock the file unless flags have _IO_USER_LOCK
2. clean everything up; includes destroying lock and setting flags to
default, not including _IO_USER_LOCK
3. unlock the file unless flags have _IO_USER_LOCK
This patch does not correct the behavious entirely. It just fixes the
clearing of _IO_USER_LOCK. The other bug (first destroying the mutex,
then unlocking it) is not as important, because the destruction will
fail, so that is a memory leak if dynamic memory is associated with
mutexes, whilst this bug can do real harm, because on files with
_IO_USER_LOCK the mutex destruction actually succeeds, and the unlock
will unlock this destroyed mutex.
This is not an issue with linuxthreads, but for example with the pthread
emulation layer in wine, that actually does associate memory with mutexes
and frees it on destruction.
<<< userlock.dpatch
#! /bin/sh -e
# DP:Fixes clearing of _IO_USER_LOCK on close, unlocking an unlocked
# DP:and destroyed mutex.
if [ $# -ne 2 ]; then
echo >&2 "`basename $0`: script expects -patch|-unpatch as argument"
exit 1
fi
case "$1" in
-patch) patch -d "$2" -f --no-backup-if-mismatch -p0 < $0;;
-unpatch) patch -d "$2" -f --no-backup-if-mismatch -R -p0 < $0;;
*)
echo >&2 "`basename $0`: script expects -patch|-unpatch as argument"
exit 1
esac
exit 0
--- libio-old/fileops.c Sun Aug 12 06:48:11 2001
+++ libio/fileops.c Tue Aug 20 21:36:08 2002
@@ -182,7 +182,7 @@
#endif
_IO_un_link ((struct _IO_FILE_plus *) fp);
- fp->_flags = _IO_MAGIC|CLOSED_FILEBUF_FLAGS;
+ fp->_flags = _IO_MAGIC|CLOSED_FILEBUF_FLAGS|(fp->_flags&_IO_USER_LOCK);
fp->_fileno = -1;
fp->_offset = _IO_pos_BAD;
>>>userlock.dpatch
-- System Information
Debian Release: 3.0
Architecture: i386
Kernel: Linux achilles.karcher.de 2.4.18 #1 Don Aug 15 23:15:36 CEST 2002 i686
Locale: LANG=de_DE.ISO-8859-1, LC_CTYPE=de_DE.ISO-8859-1
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