nfsd: check permissions when setting ACLs

Use set_posix_acl, which includes proper permission checks, instead of
calling ->set_acl directly.  Without this anyone may be able to grant
themselves permissions to a file by setting the ACL.

Lock the inode to make the new checks atomic with respect to set_acl.
(Also, nfsd was the only caller of set_acl not locking the inode, so I
suspect this may fix other races.)

This also simplifies the code, and ensures our ACLs are checked by
posix_acl_valid.

The permission checks and the inode locking were lost with commit
4ac7249e, which changed nfsd to use the set_acl inode operation directly
instead of going through xattr handlers.

Reported-by: David Sinquin <david@sinquin.eu>
[agreunba@redhat.com: use set_posix_acl]
Fixes: 4ac7249e
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 7 insertions, 9 deletions

diff --git a/fs/nfsd/nfs3acl.c b/fs/nfsd/nfs3acl.c
index 01df4cd7c753..0c890347cde3 100644
--- a/fs/nfsd/nfs3acl.c
+++ b/fs/nfsd/nfs3acl.c
@@ -95,22 +95,20 @@ static __be32 nfsd3_proc_setacl(struct svc_rqst * rqstp,
                 goto out;
 
         inode = d_inode(fh->fh_dentry);
-        if (!IS_POSIXACL(inode) || !inode->i_op->set_acl) {
-                error = -EOPNOTSUPP;
-                goto out_errno;
-        }
 
         error = fh_want_write(fh);
         if (error)
                 goto out_errno;
 
-        error = inode->i_op->set_acl(inode, argp->acl_access, ACL_TYPE_ACCESS);
+        fh_lock(fh);
+
+        error = set_posix_acl(inode, ACL_TYPE_ACCESS, argp->acl_access);
         if (error)
-                goto out_drop_write;
-        error = inode->i_op->set_acl(inode, argp->acl_default,
-                                     ACL_TYPE_DEFAULT);
+                goto out_drop_lock;
+        error = set_posix_acl(inode, ACL_TYPE_DEFAULT, argp->acl_default);
 
-out_drop_write:
+out_drop_lock:
+        fh_unlock(fh);
         fh_drop_write(fh);
 out_errno:
         nfserr = nfserrno(error);