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| author | Greg Kurz <groug@kaod.org> | 2018-11-23 13:28:03 +0100 |
|---|---|---|
| committer | Greg Kurz <groug@kaod.org> | 2018-11-23 13:28:03 +0100 |
| commit | 1d20398694a3b67a388d955b7a945ba4aa90a8a8 (patch) | |
| tree | 8c6f5b483841aad584ed6339894f0cf0d579bfb7 | |
| parent | 5298f4d67a911dd9cefa4c4185eed242074d64c2 (diff) | |
| download | qemu-1d20398694a3b67a388d955b7a945ba4aa90a8a8.zip qemu-1d20398694a3b67a388d955b7a945ba4aa90a8a8.tar.gz qemu-1d20398694a3b67a388d955b7a945ba4aa90a8a8.tar.bz2 | |
9p: fix QEMU crash when renaming files
When using the 9P2000.u version of the protocol, the following shell
command line in the guest can cause QEMU to crash:
while true; do rm -rf aa; mkdir -p a/b & touch a/b/c & mv a aa; done
With 9P2000.u, file renaming is handled by the WSTAT command. The
v9fs_wstat() function calls v9fs_complete_rename(), which calls
v9fs_fix_path() for every fid whose path is affected by the change.
The involved calls to v9fs_path_copy() may race with any other access
to the fid path performed by some worker thread, causing a crash like
shown below:
Thread 12 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
0x0000555555a25da2 in local_open_nofollow (fs_ctx=0x555557d958b8, path=0x0,
flags=65536, mode=0) at hw/9pfs/9p-local.c:59
59 while (*path && fd != -1) {
(gdb) bt
#0 0x0000555555a25da2 in local_open_nofollow (fs_ctx=0x555557d958b8,
path=0x0, flags=65536, mode=0) at hw/9pfs/9p-local.c:59
#1 0x0000555555a25e0c in local_opendir_nofollow (fs_ctx=0x555557d958b8,
path=0x0) at hw/9pfs/9p-local.c:92
#2 0x0000555555a261b8 in local_lstat (fs_ctx=0x555557d958b8,
fs_path=0x555556b56858, stbuf=0x7fff84830ef0) at hw/9pfs/9p-local.c:185
#3 0x0000555555a2b367 in v9fs_co_lstat (pdu=0x555557d97498,
path=0x555556b56858, stbuf=0x7fff84830ef0) at hw/9pfs/cofile.c:53
#4 0x0000555555a1e9e2 in v9fs_stat (opaque=0x555557d97498)
at hw/9pfs/9p.c:1083
#5 0x0000555555e060a2 in coroutine_trampoline (i0=-669165424, i1=32767)
at util/coroutine-ucontext.c:116
#6 0x00007fffef4f5600 in __start_context () at /lib64/libc.so.6
#7 0x0000000000000000 in ()
(gdb)
The fix is to take the path write lock when calling v9fs_complete_rename(),
like in v9fs_rename().
Impact: DoS triggered by unprivileged guest users.
Fixes: CVE-2018-19489
Cc: P J P <ppandit@redhat.com>
Reported-by: zhibin hu <noirfate@gmail.com>
Reviewed-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Greg Kurz <groug@kaod.org>
| -rw-r--r-- | hw/9pfs/9p.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c index 267a255..bdf7919 100644 --- a/hw/9pfs/9p.c +++ b/hw/9pfs/9p.c @@ -2855,6 +2855,7 @@ static void coroutine_fn v9fs_wstat(void *opaque) struct stat stbuf; V9fsFidState *fidp; V9fsPDU *pdu = opaque; + V9fsState *s = pdu->s; v9fs_stat_init(&v9stat); err = pdu_unmarshal(pdu, offset, "dwS", &fid, &unused, &v9stat); @@ -2920,7 +2921,9 @@ static void coroutine_fn v9fs_wstat(void *opaque) } } if (v9stat.name.size != 0) { + v9fs_path_write_lock(s); err = v9fs_complete_rename(pdu, fidp, -1, &v9stat.name); + v9fs_path_unlock(s); if (err < 0) { goto out; } |