NFSD: fix nfsd4_listxattr_validate_cookie

If LISTXATTRS is sent with a correct cookie but a small maxcount,
this could lead function nfsd4_listxattr_validate_cookie to
return NFS4ERR_BAD_COOKIE. If maxcount = 20, then second check
on function gives RHS = 3 thus any cookie larger than 3 returns
NFS4ERR_BAD_COOKIE.

There is no need to validate the cookie on the return XDR buffer
since attribute referenced by cookie will be the first in the
return buffer.

Fixes: 23e50fe3a5e6 ("nfsd: implement the xattr functions and en/decode logic")
Signed-off-by: Jorge Mora <mora@netapp.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index c719c475a068efa4cb569720a36ffa9aabfc3c2f..f0be0d6fe63fd2001692d6c7001e1e014f212bf7 100644 (file)
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -5386,16 +5386,11 @@ nfsd4_listxattr_validate_cookie(struct nfsd4_listxattrs *listxattrs,
 
        /*
         * If the cookie is larger than the maximum number we can fit
-        * in either the buffer we just got back from vfs_listxattr, or,
-        * XDR-encoded, in the return buffer, it's invalid.
+        * in the buffer we just got back from vfs_listxattr, it's invalid.
         */
        if (cookie > (listxattrs->lsxa_len) / (XATTR_USER_PREFIX_LEN + 2))
                return nfserr_badcookie;
 
-       if (cookie > (listxattrs->lsxa_maxcount /
-                     (XDR_QUADLEN(XATTR_USER_PREFIX_LEN + 2) + 4)))
-               return nfserr_badcookie;
-
        *offsetp = (u32)cookie;
        return 0;
 }