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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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21
util/osdep.c
View file

@ -33,6 +33,7 @@
extern int madvise(char *, size_t, int);
#endif
#include <dirent.h>
#include "qemu-common.h"
#include "qemu/cutils.h"
#include "qemu/sockets.h"
@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt)
return readv_writev(fd, iov, iov_cnt, true);
}
#endif
struct dirent *
qemu_dirent_dup(struct dirent *dent)
{
size_t sz = 0;
#if defined _DIRENT_HAVE_D_RECLEN
/* Avoid use of strlen() if platform supports d_reclen. */
sz = dent->d_reclen;
#endif
/*
* Test sz for zero even if d_reclen is available
* because some drivers may set d_reclen to zero.
*/
if (sz == 0) {
/* Fallback to the most portable way. */
sz = offsetof(struct dirent, d_name) +
strlen(dent->d_name) + 1;
}
return g_memdup(dent, sz);
}