Cmnt: [SRU][F][PATCH v2 0/3] CVE-2023-21400

[Koichiro Den]

On Tue, Nov 26, 2024 at 12:14:25PM +0800, Chengen Du wrote:
> CVE-2023-21400
> 
> BugLink: https://bugs.launchpad.net/bugs/2078659
> 
> SRU Justification:
> 
> [Impact]
> io_commit_cqring() writes the CQ ring tail to make it visible and also triggers any deferred work.
> When a ring is set up with IOPOLL, it doesn't require locking around the CQ ring updates.
> However, if there is deferred work that needs processing, io_queue_deferred() assumes that the completion_lock is held.
> The io_uring subsystem does not properly handle locking for rings with IOPOLL, leading to a double-free vulnerability, which can be exploited as CVE-2023-21400.
> 
> [Fix]
> There is a commit that fixed this issue.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fb348857e7b67eefe365052f1423427b66dedbf3
> 
> There is no direct upstream commit for this issue, and the patch needs to be reworked to apply to version 5.4.
> 
> [Test Plan]
> This is a timing issue that can be triggered by using the liburing library to implement a test program.
> First, set the io_uring_params flag to IORING_SETUP_IOPOLL and open an XFS file with the O_RDWR | O_DIRECT flags, as the XFS filesystem implements the iopoll function hook.
> After setting up io_uring, create two threads in the process: one thread will wait for completion queue events, and the other will continuously send readv and writev requests in sequence.
> The writev requests should include the IOSQE_IO_DRAIN flag to ensure that previous submission queue events are completed first.
> 
> The issue arises when writev requests add entries into the defer_list, but the io_iopoll_complete function consumes entries from defer_list without holding the appropriate lock.
> 
> [Where problems could occur]
> The problematic call path can be triggered under specific usage scenarios and only affects io_uring functionality.
> If the patch contains any issues, it may lead to a deadlock.
> 
> Jens Axboe (1):
>   io_uring: ensure IOPOLL locks around deferred work
> 
> Pavel Begunkov (2):
>   io_uring: remove extra check in __io_commit_cqring
>   io_uring: dont kill fasync under completion_lock

[1/3] and [2/3] seem to be not only unrelated to CVE-2023-21400 but also
unhelpful in reducing context conflicts for [3/3]. If there is still a
compelling reason to include those two for CVE-2023-21400, could you let me
know?