linux-ext4 - Re: [PATCH 02/13] rcu pathwalk: prevent bogus hard errors from may

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Message-ID: <20240205-beifahrersitz-flutwelle-efcc1a812ec6@brauner>
Date: Mon, 5 Feb 2024 13:26:22 +0100
From: Christian Brauner <brauner@...nel.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-fsdevel@...r.kernel.org, 
	Linus Torvalds <torvalds@...ux-foundation.org>, linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org, 
	Miklos Szeredi <miklos@...redi.hu>, linux-cifs@...r.kernel.org
Subject: Re: [PATCH 02/13] rcu pathwalk: prevent bogus hard errors from
 may_lookup()

On Sun, Feb 04, 2024 at 02:17:28AM +0000, Al Viro wrote:
> 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.
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---

Reviewed-by: Christian Brauner <brauner@...nel.org>