File 0108-9p-fix-QEMU-crash-when-renaming-fil.patch of Package qemu.10251

From d51b56789fcca36697ac3795f3265bb6fdff56bd Mon Sep 17 00:00:00 2001
From: Greg Kurz <groug@kaod.org>
Date: Fri, 23 Nov 2018 13:28:03 +0100
Subject: [PATCH] 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
 path=0x0, flags=65536, mode=0) at hw/9pfs/9p-local.c:59
 path=0x0) at hw/9pfs/9p-local.c:92
 fs_path=0x555556b56858, stbuf=0x7fff84830ef0) at hw/9pfs/9p-local.c:185
 path=0x555556b56858, stbuf=0x7fff84830ef0) at hw/9pfs/cofile.c:53
 at hw/9pfs/9p.c:1083
 at util/coroutine-ucontext.c:116
(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>
(cherry picked from commit 1d20398694a3b67a388d955b7a945ba4aa90a8a8)
[BR: BSC#1117275]
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 hw/9pfs/9p.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 52d46632fe..9d12bc6332 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -2808,6 +2808,7 @@ 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);
@@ -2873,7 +2874,9 @@ 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;
         }