On 18/11/22 05:01, Jeff Layton wrote:
On Thu, 2022-11-17 at 20:11 +0100, Richard Weinberger wrote:
This function is only used by NFSD to cross mount points.
If a mount point is of type auto mount, follow_down() will
not uncover it. Add LOOKUP_AUTOMOUNT to the lookup flags
to have ->d_automount() called when NFSD walks down the
mount tree.
Signed-off-by: Richard Weinberger <richard@xxxxxx>
---
fs/namei.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/namei.c b/fs/namei.c
index 578c2110df02..000c4b84e6be 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1462,7 +1462,7 @@ int follow_down(struct path *path)
{
struct vfsmount *mnt = path->mnt;
bool jumped;
- int ret = traverse_mounts(path, &jumped, NULL, 0);
+ int ret = traverse_mounts(path, &jumped, NULL, LOOKUP_AUTOMOUNT);
if (path->mnt != mnt)
mntput(mnt);
What happens when CROSSMOUNT isn't enabled and someone tries to stroll
into an automount point? I'm guessing the automount happens but the
export is denied? It seems like LOOKUP_AUTOMOUNT ought to be conditional
on the parent export having CROSSMOUNT set.
There's also another caller of follow_down too, the UNIX98 pty code.
This may be harmless for it, but it'd be best not to perturb that if we
can help it.
Maybe follow_down can grow a lookupflags argument?es, I think that's needed too.
Changing the core VFS unconditionally ricks breaking things.
For example this:
if (!(lookup_flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
LOOKUP_OPEN | LOOKUP_CREATE |
LOOKUP_AUTOMOUNT)) &&
dentry->d_inode)
will never be true now so that, at the least, the handling of this case
will change for automount(8). I don't remember now the reasons behind
doing this but I do remember there was a special case that needed to
be handled by it.
Ian
