[PATCH] r/o bind mounts: elevate write count for xattr_permission() callers

This basically audits the callers of xattr_permission(), which calls
permission() and can perform writes to the filesystem.

[AV: add missing parts - removexattr() and nfsd posix acls, plug for a leak
spotted by Miklos]

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 18a4cc9feeb3..626dfd38528f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -2086,6 +2086,9 @@ nfsd_set_posix_acl(struct svc_fh *fhp, int type, struct posix_acl *acl)
         } else
                 size = 0;
 
+        error = mnt_want_write(fhp->fh_export->ex_path.mnt);
+        if (error)
+                goto getout;
         if (size)
                 error = vfs_setxattr(fhp->fh_dentry, name, value, size, 0);
         else {
@@ -2097,6 +2100,7 @@ nfsd_set_posix_acl(struct svc_fh *fhp, int type, struct posix_acl *acl)
                                 error = 0;
                 }
         }
+        mnt_drop_write(fhp->fh_export->ex_path.mnt);
 
 getout:
         kfree(value);