[PATCH AUTOSEL 4.4 17/63] cifs: Fix NULL pointer dereference of devname

Sasha Levin
2019-03-27T18:36:56Z

From: Yao Liu <yotta.liu@ucloud.cn>

[ Upstream commit 68e2672f8fbd1e04982b8d2798dd318bf2515dd2 ]

There is a NULL pointer dereference of devname in strspn()

The oops looks something like:

CIFS: Attempting to mount (null)
BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
...
RIP: 0010:strspn+0x0/0x50
...
Call Trace:
? cifs_parse_mount_options+0x222/0x1710 [cifs]
? cifs_get_volume_info+0x2f/0x80 [cifs]
cifs_setup_volume_info+0x20/0x190 [cifs]
cifs_get_volume_info+0x50/0x80 [cifs]
cifs_smb3_do_mount+0x59/0x630 [cifs]
? ida_alloc_range+0x34b/0x3d0
cifs_do_mount+0x11/0x20 [cifs]
mount_fs+0x52/0x170
vfs_kern_mount+0x6b/0x170
do_mount+0x216/0xdc0
ksys_mount+0x83/0xd0
__x64_sys_mount+0x25/0x30
do_syscall_64+0x65/0x220
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fix this by adding a NULL check on devname in cifs_parse_devname()

Signed-off-by: Yao Liu <yotta.liu@ucloud.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/cifs/connect.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index eacf57c24ca9..9cb72fd40eff 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1255,6 +1255,11 @@ cifs_parse_devname(const char *devname, struct smb_vol *vol)
const char *delims = "/\\";
size_t len;

+ if (unlikely(!devname || !*devname)) {
+ cifs_dbg(VFS, "Device name not specified.\n");
+ return -EINVAL;
+ }
+
/* make sure we have a valid UNC double delimiter prefix */
len = strspn(devname, delims);
if (len != 2)
--
2.19.1