Re: [PATCH 5.10/5.15] io_uring: fix registered files leak

[Jens Axboe]

On 3/12/24 8:23 AM, Fedor Pchelkin wrote:
> No upstream commit exists for this patch.
> 
> Backport of commit 705318a99a13 ("io_uring/af_unix: disable sending
> io_uring over sockets") introduced registered files leaks in 5.10/5.15
> stable branches when CONFIG_UNIX is enabled.
> 
> The 5.10/5.15 backports removed io_sqe_file_register() calls from
> io_install_fixed_file() and __io_sqe_files_update() so that newly added
> files aren't passed to UNIX-related skbs and thus can't be put during
> unregistering process. Skbs in the ring socket receive queue are released
> but there is no skb having reference to the newly updated file.
> 
> In other words, when CONFIG_UNIX is enabled there would be no fput() when
> files are unregistered for the corresponding fget() from
> io_install_fixed_file() and __io_sqe_files_update().
> 
> Drop several code paths related to SCM_RIGHTS as a partial change from
> commit 6e5e6d274956 ("io_uring: drop any code related to SCM_RIGHTS").
> This code is useless in stable branches now, too, but is causing leaks in
> 5.10/5.15.
> 
> As stated above, the affected code was removed in upstream by
> commit 6e5e6d274956 ("io_uring: drop any code related to SCM_RIGHTS").
> 
> Fresher stables from 6.1 have io_file_need_scm() stub function which
> usage is effectively equivalent to dropping most of SCM-related code.
> 
> 5.4 seems not to be affected with this problem since SCM-related
> functions have been dropped there by the backport-patch.
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Fixes: 705318a99a13 ("io_uring/af_unix: disable sending io_uring over sockets")
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
> ---
> I feel io_uring-SCM related code should be dropped entirely from the
> stable branches as the backports already differ greatly between versions
> and some parts are still kept, some have been dropped in a non-consistent
> order. Though this might contradict with stable kernel rules or be
> inappropriate for some other reason.

Looks fine to me, and I agree, it makes much more sense to drop it all
from 5.10/5.15-stable as well to keep them in sync with upstream. And I
think this is fine for stable, dropping code is always a good thing.

-- 
Jens Axboe