autofs: fix symlinks aren't checked for expiry

The autofs4 module doesn't consider symlinks for expire as it did in the
older autofs v3 module (so it's actually a long standing regression).

The user space daemon has focused on the use of bind mounts instead of
symlinks for a long time now and that's why this has not been noticed.
But with the future addition of amd map parsing to automount(8), not to
mention amd itself (of am-utils), symlink expiry will be needed.

The direct and offset mount types can't be symlinks and the tree mounts of
version 4 were always real mounts so only indirect mounts need expire
symlinks.

Since the current users of the autofs4 module haven't reported this as a
problem to date this patch probably isn't a candidate for backport to
stable.

Signed-off-by: Ian Kent <ikent@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 3d9d3f5d5dda..394e90b02c5e 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -402,6 +402,20 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb,
 			goto next;
 		}
 
+		if (dentry->d_inode && S_ISLNK(dentry->d_inode->i_mode)) {
+			DPRINTK("checking symlink %p %.*s",
+				dentry, (int)dentry->d_name.len, dentry->d_name.name);
+			/*
+			 * A symlink can't be "busy" in the usual sense so
+			 * just check last used for expire timeout.
+			 */
+			if (autofs4_can_expire(dentry, timeout, do_now)) {
+				expired = dentry;
+				goto found;
+			}
+			goto next;
+		}
+
 		if (simple_empty(dentry))
 			goto next;