[PATCH] autofs4: check for directory re-create in lookup
This problem was identified and fixed some time ago by Jeff Moyer but it fell
through the cracks somehow.
It is possible that a user space application could remove and re-create a
directory during a request. To avoid returning a failure from lookup
incorrectly when our current dentry is unhashed we need to check if another
positive, hashed dentry matching this one exists and if so return it instead
of a fail.
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 47adf27..b463104 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -655,14 +655,29 @@
/*
* If this dentry is unhashed, then we shouldn't honour this
- * lookup even if the dentry is positive. Returning ENOENT here
- * doesn't do the right thing for all system calls, but it should
- * be OK for the operations we permit from an autofs.
+ * lookup. Returning ENOENT here doesn't do the right thing
+ * for all system calls, but it should be OK for the operations
+ * we permit from an autofs.
*/
if (dentry->d_inode && d_unhashed(dentry)) {
+ /*
+ * A user space application can (and has done in the past)
+ * remove and re-create this directory during the callback.
+ * This can leave us with an unhashed dentry, but a
+ * successful mount! So we need to perform another
+ * cached lookup in case the dentry now exists.
+ */
+ struct dentry *parent = dentry->d_parent;
+ struct dentry *new = d_lookup(parent, &dentry->d_name);
+ if (new != NULL)
+ dentry = new;
+ else
+ dentry = ERR_PTR(-ENOENT);
+
if (unhashed)
dput(unhashed);
- return ERR_PTR(-ENOENT);
+
+ return dentry;
}
if (unhashed)
