NFS4: Avoid potential NULL pointer dereference in decode_and_add_ds().

On Mon, 17 Jan 2011, Mi Jinlong wrote:

>
>
> Jesper Juhl:
> > strrchr() can return NULL if nothing is found. If this happens we'll
> > dereference a NULL pointer in
> > fs/nfs/nfs4filelayoutdev.c::decode_and_add_ds().
> >
> > I tried to find some other code that guarantees that this can never
> > happen but I was unsuccessful. So, unless someone else can point to some
> > code that ensures this can never be a problem, I believe this patch is
> > needed.
> >
> > While I was changing this code I also noticed that all the dprintk()
> > statements, except one, start with "%s:". The one missing the ":" I added
> > it to.
>
>   Maybe another one also should be changed at decode_and_add_ds() at line 243:
>
>    243  printk("%s Decoded address and port %s\n", __func__, buf);
>
Missed that one. Thanks.
Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4filelayoutdev.c

@@ -214,7 +214,7 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
 
 	/* ipv6 length plus port is legal */
 	if (rlen > INET6_ADDRSTRLEN + 8) {
-		dprintk("%s Invalid address, length %d\n", __func__,
+		dprintk("%s: Invalid address, length %d\n", __func__,
 			rlen);
 		goto out_err;
 	}
@@ -225,6 +225,11 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
 	/* replace the port dots with dashes for the in4_pton() delimiter*/
 	for (i = 0; i < 2; i++) {
 		char *res = strrchr(buf, '.');
+		if (!res) {
+			dprintk("%s: Failed finding expected dots in port\n",
+				__func__);
+			goto out_free;
+		}
 		*res = '-';
 	}
 
@@ -240,7 +245,7 @@ decode_and_add_ds(__be32 **pp, struct inode *inode)
 	port = htons((tmp[0] << 8) | (tmp[1]));
 
 	ds = nfs4_pnfs_ds_add(inode, ip_addr, port);
-	dprintk("%s Decoded address and port %s\n", __func__, buf);
+	dprintk("%s: Decoded address and port %s\n", __func__, buf);
 out_free:
 	kfree(buf);
 out_err: