Commit cdb67fde authored by Al Viro's avatar Al Viro
Browse files

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: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 583340de

fs/namei.c

+5 −1
Original line number Diff line number Diff line
@@ -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);