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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Yao Liu <yotta.liu@ucloud.cn>,
        Steve French <stfrench@microsoft.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 040/187] cifs: Fix NULL pointer dereference of devname
Date:   Thu,  4 Apr 2019 10:46:17 +0200
Message-Id: <20190404084604.963447087@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

[ 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 a5ea742654aa..f31339db45fd 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1347,6 +1347,11 @@ 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