[PATCH] r/o bind mounts: check mnt instead of superblock directly

If we depend on the inodes for writeability, we will not catch the r/o mounts
when implemented.

This patches uses __mnt_want_write().  It does not guarantee that the mount
will stay writeable after the check.  But, this is OK for one of the checks
because it is just for a printk().

The other two are probably unnecessary and duplicate existing checks in the
VFS.  This won't make them better checks than before, but it will make them
detect r/o mounts.

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
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, 3 insertions, 2 deletions

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 626dfd38528f..304bf5f643c9 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1912,7 +1912,7 @@ nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
                 inode->i_mode,
                 IS_IMMUTABLE(inode)?    " immut" : "",
                 IS_APPEND(inode)?       " append" : "",
-                IS_RDONLY(inode)?       " ro" : "");
+                __mnt_is_readonly(exp->ex_path.mnt)?    " ro" : "");
         dprintk("      owner %d/%d user %d/%d\n",
                 inode->i_uid, inode->i_gid, current->fsuid, current->fsgid);
 #endif
@@ -1923,7 +1923,8 @@ nfsd_permission(struct svc_rqst *rqstp, struct svc_export *exp,
          */
         if (!(acc & MAY_LOCAL_ACCESS))
                 if (acc & (MAY_WRITE | MAY_SATTR | MAY_TRUNC)) {
-                        if (exp_rdonly(rqstp, exp) || IS_RDONLY(inode))
+                        if (exp_rdonly(rqstp, exp) ||
+                            __mnt_is_readonly(exp->ex_path.mnt))
                                 return nfserr_rofs;
                         if (/* (acc & MAY_WRITE) && */ IS_IMMUTABLE(inode))
                                 return nfserr_perm;