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9pfs: Fix segfault in do_readdir_many caused by struct dirent overread

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`struct dirent' returned from readdir(3) could be shorter (or longer)
than `sizeof(struct dirent)', thus memcpy of sizeof length will overread
into unallocated page causing SIGSEGV. Example stack trace:

 #0  0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + 0x497eed)
 #1  0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + 0x4982e9)
 #2  0x0000555555eb7983 coroutine_trampoline (/usr/bin/qemu-system-x86_64 + 0x963983)
 #3  0x00007ffff73e0be0 n/a (n/a + 0x0)

While fixing this, provide a helper for any future `struct dirent' cloning.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
Cc: qemu-stable@nongnu.org
Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
Tested-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Acked-by: Greg Kurz <groug@kaod.org>
Tested-by: Vitaly Chikunov <vt@altlinux.org>
Message-Id: <20220216181821.3481527-1-vt@altlinux.org>
[C.S. - Fix typo in source comment. ]
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
This commit is contained in:
Vitaly Chikunov 2022-02-16 21:18:21 +03:00 • committed by Christian Schoenebeck
parent 494fbbd3ed
commit e64e27d5cb
5 changed files with 55 additions and 5 deletions
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13
include/qemu/osdep.h
View file

@ -805,6 +805,19 @@ static inline int platform_does_not_support_system(const char *command)
}
#endif /* !HAVE_SYSTEM_FUNCTION */
/**
* Duplicate directory entry @dent.
*
* It is highly recommended to use this function instead of open coding
* duplication of @c dirent objects, because the actual @c struct @c dirent
* size may be bigger or shorter than @c sizeof(struct dirent) and correct
* handling is platform specific (see gitlab issue #841).
*
* @dent - original directory entry to be duplicated
* @returns duplicated directory entry which should be freed with g_free()
*/
struct dirent *qemu_dirent_dup(struct dirent *dent);
#ifdef __cplusplus
}
#endif