On Wed, Jan 01, 2020 at 12:43:24AM +0000, Al Viro wrote:
I'm not sure if you have caught anything else, but we really, really should *NOT* consider the LAST_BIND as "maybe we should follow the result" material. So at least the following is needed; could you check if anything else remains with that applied?
diff --git a/fs/namei.c b/fs/namei.c index d6c91d1e88cb..d4fbbda8a7ff 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2656,10 +2656,7 @@ mountpoint_last(struct nameidata *nd) nd->flags &= ~LOOKUP_PARENT; if (unlikely(nd->last_type != LAST_NORM)) {
error = handle_dots(nd, nd->last_type);if (error)return error;path.dentry = dget(nd->path.dentry);
return handle_dots(nd, nd->last_type);
Note, BTW, that lookup_last() (aka walk_component()) does just that - we only hit step_into() on LAST_NORM. The same goes for do_last(). mountpoint_last() not doing the same is _not_ intentional - it's definitely a bug.
Consider your testcase; link points to . here. So the only thing you could expect from trying to follow it would be the directory 'link' lives in. And you don't have it when you reach the fscker via /proc/self/fd/3; what happens instead is nd->path set to ./link (by nd_jump_link()) *AND* step_into() called, pushing the same ./link onto stack. It violates all kinds of assumptions made by fs/namei.c - when pushing a symlink onto stack nd->path is expected to contain the base directory for resolving it.
I'm fairly sure that this is the cause of at least some of the insanity you've caught; there always could be something else, of course, but this hole needs to be closed in any case.