diff options
authorGreg Kurz <groug@kaod.org>2018-11-23 13:28:03 +0100
committerGreg Kurz <groug@kaod.org>2018-11-23 13:28:03 +0100
commit1d20398694a3b67a388d955b7a945ba4aa90a8a8 (patch)
parent5298f4d67a911dd9cefa4c4185eed242074d64c2 (diff)
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>
1 files changed, 3 insertions, 0 deletions
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 267a25533b..bdf7919abf 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;
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;