NFS: fs_context: validate UDP retrans to prevent shift out-of-bounds

Fix shift out-of-bounds in xprt_calc_majortimeo(). This is caused
by a garbage timeout (retrans) mount option being passed to nfs mount,
in this case from syzkaller.

If the protocol is XPRT_TRANSPORT_UDP, then 'retrans' is a shift
value for a 64-bit long integer, so 'retrans' cannot be >= 64.
If it is >= 64, fail the mount and return an error.

Fixes: 9954bf92c0cd ("NFS: Move mount parameterisation bits into their own file")
Reported-by: syzbot+ba2e91df8f74809417fa@syzkaller.appspotmail.com
Reported-by: syzbot+f3a0fa110fd630ab56c8@syzkaller.appspotmail.com
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: linux-nfs@vger.kernel.org
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 971a925..902db12 100644 (file)
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -973,6 +973,15 @@ static int nfs23_parse_monolithic(struct fs_context *fc,
                        memset(mntfh->data + mntfh->size, 0,
                               sizeof(mntfh->data) - mntfh->size);
 
+               /*
+                * for proto == XPRT_TRANSPORT_UDP, which is what uses
+                * to_exponential, implying shift: limit the shift value
+                * to BITS_PER_LONG (majortimeo is unsigned long)
+                */
+               if (!(data->flags & NFS_MOUNT_TCP)) /* this will be UDP */
+                       if (data->retrans >= 64) /* shift value is too large */
+                               goto out_invalid_data;
+
                /*
                 * Translate to nfs_fs_context, which nfs_fill_super
                 * can deal with.
@@ -1073,6 +1082,9 @@ out_no_address:
 
 out_invalid_fh:
        return nfs_invalf(fc, "NFS: invalid root filehandle");
+
+out_invalid_data:
+       return nfs_invalf(fc, "NFS: invalid binary mount data");
 }
 
 #if IS_ENABLED(CONFIG_NFS_V4)