orangefs: fix xattr related buffer overflow...

Willy Tarreau <[e-mail]> forwarded me a message from
Disclosure <[e-mail]> with the following
warning:

> The helper `xattr_key()` uses the pointer variable in the loop condition
> rather than dereferencing it. As `key` is incremented, it remains non-NULL
> (until it runs into unmapped memory), so the loop does not terminate on
> valid C strings and will walk memory indefinitely, consuming CPU or hanging
> the thread.

I easily reproduced this with setfattr and getfattr, causing a kernel
oops, hung user processes and corrupted orangefs files. Disclosure
sent along a diff (not a patch) with a suggested fix, which I based
this patch on.

After xattr_key started working right, xfstest generic/069 exposed an
xattr related memory leak that lead to OOM. xattr_key returns
a hashed key. When adding xattrs to the orangefs xattr cache, orangefs
used hash_add, a kernel hashing macro. hash_add also hashes the key using
hash_log which resulted in additions to the xattr cache going to the wrong
hash bucket. generic/069 tortures a single file and orangefs does a
getattr for the xattr "security.capability" every time. Orangefs
negative caches on xattrs which includes a kmalloc. Since adds to the
xattr cache were going to the wrong bucket, every getattr for
"security.capability" resulted in another kmalloc, none of which were
ever freed.

I changed the two uses of hash_add to hlist_add_head instead
and the memory leak ceased and generic/069 quit throwing furniture.

Signed-off-by: Mike Marshall <[e-mail]>
Reported-by: Stanislav Fort of Aisle Research <[e-mail]>

fs/orangefs/xattr.c

···
 static unsigned int xattr_key(const char *key)
 {
 	unsigned int i = 0;
-	while (key)
+	if (!key)
+		return 0;
+	while (*key)
 		i += *key++;
 	return i % 16;
 }
···
 				cx->length = -1;
 				cx->timeout = jiffies +
 				    orangefs_getattr_timeout_msecs*HZ/1000;
-				hash_add(orangefs_inode->xattr_cache, &cx->node,
-				    xattr_key(cx->key));
+				hlist_add_head( &cx->node,
+                                   &orangefs_inode->xattr_cache[xattr_key(cx->key)]);
 			}
 		}
 		goto out_release_op;
···
 			memcpy(cx->val, buffer, length);
 			cx->length = length;
 			cx->timeout = jiffies + HZ;
-			hash_add(orangefs_inode->xattr_cache, &cx->node,
-			    xattr_key(cx->key));
+			hlist_add_head(&cx->node,
+				&orangefs_inode->xattr_cache[xattr_key(cx->key)]);
 		}
 	}