NACK: [SRU][F][PATCH 0/1] CVE-2023-21400

[Roxana Nicolescu]

On 08/11/2024 03:49, 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
>
>   fs/io_uring.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
To close the thread.