From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:41819) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hB45b-0002Ll-TZ for qemu-devel@nongnu.org; Mon, 01 Apr 2019 17:03:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hB45a-00044i-N4 for qemu-devel@nongnu.org; Mon, 01 Apr 2019 17:03:31 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55734) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hB45a-0003yF-Cf for qemu-devel@nongnu.org; Mon, 01 Apr 2019 17:03:30 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x31L1p2c061963 for ; Mon, 1 Apr 2019 17:03:19 -0400 Received: from e14.ny.us.ibm.com (e14.ny.us.ibm.com [129.33.205.204]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rksw4s3pc-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 01 Apr 2019 17:03:18 -0400 Received: from localhost by e14.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 1 Apr 2019 22:03:17 +0100 From: Michael Roth Date: Mon, 1 Apr 2019 16:00:09 -0500 In-Reply-To: <20190401210011.16009-1-mdroth@linux.vnet.ibm.com> References: <20190401210011.16009-1-mdroth@linux.vnet.ibm.com> Message-Id: <20190401210011.16009-96-mdroth@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH 95/97] 9p: fix QEMU crash when renaming files List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Greg Kurz , P J P From: Greg Kurz 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 Reported-by: zhibin hu Reviewed-by: Prasad J Pandit Signed-off-by: Greg Kurz (cherry picked from commit 1d20398694a3b67a388d955b7a945ba4aa90a8a8) Signed-off-by: Michael Roth --- hw/9pfs/9p.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c index eef289e394..88e523f8dd 100644 --- a/hw/9pfs/9p.c +++ b/hw/9pfs/9p.c @@ -2840,6 +2840,7 @@ 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); @@ -2905,7 +2906,9 @@ 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; } -- 2.17.1