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, 8 insertions, 8 deletions

diff --git a/fs/nfsd/nfs4acl.c b/fs/nfsd/nfs4acl.c
index 6adabd6049b7..71292a0d6f09 100644
--- a/fs/nfsd/nfs4acl.c
+++ b/fs/nfsd/nfs4acl.c
@@ -770,9 +770,6 @@ nfsd4_set_nfs4_acl(struct svc_rqst *rqstp, struct svc_fh *fhp,
         dentry = fhp->fh_dentry;
         inode = d_inode(dentry);
 
-        if (!inode->i_op->set_acl || !IS_POSIXACL(inode))
-                return nfserr_attrnotsupp;
-
         if (S_ISDIR(inode->i_mode))
                 flags = NFS4_ACL_DIR;
 
@@ -782,16 +779,19 @@ nfsd4_set_nfs4_acl(struct svc_rqst *rqstp, struct svc_fh *fhp,
         if (host_error < 0)
                 goto out_nfserr;
 
-        host_error = inode->i_op->set_acl(inode, pacl, ACL_TYPE_ACCESS);
+        fh_lock(fhp);
+
+        host_error = set_posix_acl(inode, ACL_TYPE_ACCESS, pacl);
         if (host_error < 0)
-                goto out_release;
+                goto out_drop_lock;
 
         if (S_ISDIR(inode->i_mode)) {
-                host_error = inode->i_op->set_acl(inode, dpacl,
-                                                  ACL_TYPE_DEFAULT);
+                host_error = set_posix_acl(inode, ACL_TYPE_DEFAULT, dpacl);
         }
 
-out_release:
+out_drop_lock:
+        fh_unlock(fhp);
+
         posix_acl_release(pacl);
         posix_acl_release(dpacl);
 out_nfserr: