autofs4: detect invalid direct mount requests

autofs v5 direct and offset mounts within an autofs filesystem are
triggered by existing autofs triger mounts so the mount point dentry must
be positive.  If the mount point dentry is negative then the trigger
doesn't exist so we can return fail immediately.

Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index 3458dbc8fff0b1b7f2b709c819fab9cd1971977c..bcb6c5265467f4306721848e7076b327f0151aa2 100644 (file)
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -328,6 +328,10 @@ int autofs4_wait(struct autofs_sb_info *sbi, struct dentry *dentry,
        if (sbi->catatonic)
                return -ENOENT;
 
+       if (!dentry->d_inode &&
+           (sbi->type & (AUTOFS_TYPE_DIRECT | AUTOFS_TYPE_OFFSET)))
+               return -ENOENT;
+
        name = kmalloc(NAME_MAX + 1, GFP_KERNEL);
        if (!name)
                return -ENOMEM;