From cdb67fdeed72248475b1c849699495ef290a1634 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 29 Sep 2023 21:11:41 -0400 Subject: rcu pathwalk: prevent bogus hard errors from may_lookup() If lazy call of ->permission() returns a hard error, check that try_to_unlazy() succeeds before returning it. That both makes life easier for ->permission() instances and closes the race in ENOTDIR handling - it is possible that positive d_can_lookup() seen in link_path_walk() applies to the state *after* unlink() + mkdir(), while nd->inode matches the state prior to that. Normally seeing e.g. EACCES from permission check in rcu pathwalk means that with some timings non-rcu pathwalk would've run into the same; however, running into a non-executable regular file in the middle of a pathname would not get to permission check - it would fail with ENOTDIR instead. Reviewed-by: Christian Brauner Signed-off-by: Al Viro --- fs/namei.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'fs/namei.c') diff --git a/fs/namei.c b/fs/namei.c index 4e0de939fea1..9342fa6a38c2 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1717,7 +1717,11 @@ static inline int may_lookup(struct mnt_idmap *idmap, { if (nd->flags & LOOKUP_RCU) { int err = inode_permission(idmap, nd->inode, MAY_EXEC|MAY_NOT_BLOCK); - if (err != -ECHILD || !try_to_unlazy(nd)) + if (!err) // success, keep going + return 0; + if (!try_to_unlazy(nd)) + return -ECHILD; // redo it all non-lazy + if (err != -ECHILD) // hard error return err; } return inode_permission(idmap, nd->inode, MAY_EXEC); -- cgit v1.2.3-70-g09d2