From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 84F488F70 for ; Tue, 23 Jul 2024 13:52:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721742764; cv=none; b=MIOJ4sPd7d56s0soMAbXUCeO3NnnwFV/Lvi5d7hY5lV7ovguy5oXpAflhh4C7AgRt0hj2+E8sOSub+UBSkog81uhQgxyX7JGH7w/w2ZNvorhM0FJ1xq6MLKJc6aVS+58p4/NUH4e3CSP3EMSfjivbhyEtBH6ZXGxslNJ9AZJekQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721742764; c=relaxed/simple; bh=U0OPuNQpp7Vdpx7uvYwVWpaGqdc+O1V8tPKvSnyKra4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=j28AMtRaBSyPQtGJMETWqLunY22eWwNnjCSggdEKtuhzIH4BIOhVIAuTy514dxJOs1zpbMnF/bW4FPcRe4Oi069eFiT+UJ9NmbBM3X4fkve31yjdvv1tYVsjuSlABHYAuBjNCi37PuH/6LrEya4SpVklt/LE2hxLE8BT8N5K16Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=AJ5SIkxf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="AJ5SIkxf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2F6DC4AF0A; Tue, 23 Jul 2024 13:52:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1721742764; bh=U0OPuNQpp7Vdpx7uvYwVWpaGqdc+O1V8tPKvSnyKra4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=AJ5SIkxfF9IdKsJoUNIuz9H3vx4TdkF3fD2fQVlr5LIGSxkmf83uRDLrIcb2VfNy+ GFri+IjmmOMKgt5w+ux1/N+ytQsvqmW71vKRT5Zu0QwARGkIxd10PaTEZnDXPmppO1 FP6NerHzMkllqOLANDhscXfL927YmUeTozOvQx18= Date: Tue, 23 Jul 2024 15:52:41 +0200 From: Greg KH To: Jann Horn Cc: stable@vger.kernel.org Subject: Re: [PATCH stable 4.19-6.6] filelock: Remove locks reliably when fcntl/close race is detected Message-ID: <2024072310-anointer-unusable-fd67@gregkh> References: <20240722142250.155873-1-jannh@google.com> <2024072315-oppressor-traps-56a1@gregkh> <2024072353-deceptive-subsector-54fb@gregkh> <2024072328-delirious-wired-1720@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Jul 23, 2024 at 03:36:07PM +0200, Jann Horn wrote: > On Tue, Jul 23, 2024 at 3:09 PM Greg KH wrote: > > > > On Tue, Jul 23, 2024 at 03:00:28PM +0200, Greg KH wrote: > > > On Tue, Jul 23, 2024 at 02:56:08PM +0200, Greg KH wrote: > > > > On Mon, Jul 22, 2024 at 04:22:50PM +0200, Jann Horn wrote: > > > > > commit 3cad1bc010416c6dd780643476bc59ed742436b9 upstream. > > > > > > > > > > When fcntl_setlk() races with close(), it removes the created lock with > > > > > do_lock_file_wait(). > > > > > However, LSMs can allow the first do_lock_file_wait() that created the lock > > > > > while denying the second do_lock_file_wait() that tries to remove the lock. > > > > > In theory (but AFAIK not in practice), posix_lock_file() could also fail to > > > > > remove a lock due to GFP_KERNEL allocation failure (when splitting a range > > > > > in the middle). > > > > > > > > > > After the bug has been triggered, use-after-free reads will occur in > > > > > lock_get_status() when userspace reads /proc/locks. This can likely be used > > > > > to read arbitrary kernel memory, but can't corrupt kernel memory. > > > > > This only affects systems with SELinux / Smack / AppArmor / BPF-LSM in > > > > > enforcing mode and only works from some security contexts. > > > > > > > > > > Fix it by calling locks_remove_posix() instead, which is designed to > > > > > reliably get rid of POSIX locks associated with the given file and > > > > > files_struct and is also used by filp_flush(). > > > > > > > > > > Fixes: c293621bbf67 ("[PATCH] stale POSIX lock handling") > > > > > Cc: stable@kernel.org > > > > > Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=2563 > > > > > Signed-off-by: Jann Horn > > > > > Link: https://lore.kernel.org/r/20240702-fs-lock-recover-2-v1-1-edd456f63789@google.com > > > > > Reviewed-by: Jeff Layton > > > > > Signed-off-by: Christian Brauner > > > > > [stable fixup: ->c.flc_type was ->fl_type in older kernels] > > > > > Signed-off-by: Jann Horn > > > > > --- > > > > > fs/locks.c | 9 ++++----- > > > > > 1 file changed, 4 insertions(+), 5 deletions(-) > > > > > > > > > > diff --git a/fs/locks.c b/fs/locks.c > > > > > index fb717dae9029..31659a2d9862 100644 > > > > > --- a/fs/locks.c > > > > > +++ b/fs/locks.c > > > > > @@ -2381,8 +2381,9 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, > > > > > error = do_lock_file_wait(filp, cmd, file_lock); > > > > > > > > > > /* > > > > > - * Attempt to detect a close/fcntl race and recover by releasing the > > > > > - * lock that was just acquired. There is no need to do that when we're > > > > > + * Detect close/fcntl races and recover by zapping all POSIX locks > > > > > + * associated with this file and our files_struct, just like on > > > > > + * filp_flush(). There is no need to do that when we're > > > > > * unlocking though, or for OFD locks. > > > > > */ > > > > > if (!error && file_lock->fl_type != F_UNLCK && > > > > > @@ -2397,9 +2398,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd, > > > > > f = files_lookup_fd_locked(files, fd); > > > > > spin_unlock(&files->file_lock); > > > > > if (f != filp) { > > > > > - file_lock->fl_type = F_UNLCK; > > > > > - error = do_lock_file_wait(filp, cmd, file_lock); > > > > > - WARN_ON_ONCE(error); > > > > > + locks_remove_posix(filp, files); > > > > > > > > Wait, this breaks the build on 5.4.y with the error: > > > > > > > > fs/locks.c: In function ‘fcntl_setlk’: > > > > fs/locks.c:2545:50: error: ‘files’ undeclared (first use in this function); did you mean ‘file’? > > > > 2545 | locks_remove_posix(filp, files); > > > > | ^~~~~ > > > > | file > > > > > > > > I didn't do test-builds yesterday, my fault for not noticing this yet. > > > > > > > > I've dropped this from the 5.4.y queues for now, can you fix this up and send > > > > an updated version, or give me a hint as to what to do instead? Odd that this > > > > works on 4.19.y, let me see why... > > > > > > Ah, I see why, it applied to the wrong function in 4.19 and that didn't > > > get built on my test systems (i.e. 64bit only.) And I see how to fix > > > this up, let me go do that now, sorry for the noise. > > > > And it's fixed now on 5.4.y as well, I just reference current->files and > > all is good. > > Uuuugh, but actually as you mentioned the buggy code is duplicated > (which was why you had that build success for 4.19). Even in mainline > there are two versions and I missed the one for 64-bit offsets on > 32-bit systems. > > So I guess I gotta go back and send another patch to mainline for the > second path, and then get that through stable too... bleh. Hey, the stable review process found a bug in mainline, that's a good thing! :) If you need help backporting, I'm glad to do so. thanks, greg k-h