ovl: listxattr: use strnlen()

Be defensive about what underlying fs provides us in the returned xattr
list buffer.  If it's not properly null terminated, bail out with a warning
insead of BUG.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org>

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 1878591..c75625c 100644 (file)
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -255,7 +255,8 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 {
        struct dentry *realdentry = ovl_dentry_real(dentry);
        ssize_t res;
-       int off;
+       size_t len;
+       char *s;
        const struct cred *old_cred;
 
        old_cred = ovl_override_creds(dentry->d_sb);
@@ -265,17 +266,19 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
                return res;
 
        /* filter out private xattrs */
-       for (off = 0; off < res;) {
-               char *s = list + off;
-               size_t slen = strlen(s) + 1;
+       for (s = list, len = res; len;) {
+               size_t slen = strnlen(s, len) + 1;
 
-               BUG_ON(off + slen > res);
+               /* underlying fs providing us with an broken xattr list? */
+               if (WARN_ON(slen > len))
+                       return -EIO;
 
+               len -= slen;
                if (ovl_is_private_xattr(s)) {
                        res -= slen;
-                       memmove(s, s + slen, res - off);
+                       memmove(s, s + slen, len);
                } else {
-                       off += slen;
+                       s += slen;
                }
        }