cifs: Fix NULL pointer dereference of devname

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>

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 8463c940e0e59779390b210fa3ebba45df86f80b..2ed773b395a480155db9a6797c0e95d47547c796 100644 (file)
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1486,6 +1486,11 @@ 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)