fuse: fix permission checking on sticky directories

The VFS checks sticky bits on the parent directory even if the filesystem
defines it's own ->permission().  In some situations (sshfs, mountlo, etc) the
user does have permission to delete a file even if the attribute based
checking would not allow it.

So work around this by storing the permission bits separately and returning
them in stat(), but cutting the permission bits off from inode->i_mode.

This is slightly hackish, but it's probably not worth it to add new
infrastructure in VFS and a slight performance penalty for all filesystems,
just for the sake of fuse.

[Jan Engelhardt] cosmetic fixes
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e0555d68b4a7..1764506fdd11 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -63,6 +63,10 @@ struct fuse_inode {
 
         /** Time in jiffies until the file attributes are valid */
         u64 i_time;
+
+        /** The sticky bit in inode->i_mode may have been removed, so
+            preserve the original mode */
+        mode_t orig_i_mode;
 };
 
 /** FUSE specific file data */