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io_uring: Fix registered ring file refcount leak

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Currently, io_uring_unreg_ringfd() (which cleans up registered rings) is
only called on exit, but __io_uring_free (which frees the tctx in which the
registered ring pointers are stored) is also called on execve (via
begin_new_exec -> io_uring_task_cancel -> __io_uring_cancel ->
io_uring_cancel_generic -> __io_uring_free).

This means: A process going through execve while having registered rings
will leak references to the rings' `struct file`.

Fix it by zapping registered rings on execve(). This is implemented by
moving the io_uring_unreg_ringfd() from io_uring_files_cancel() into its
callee __io_uring_cancel(), which is called from io_uring_task_cancel() on
execve.

This could probably be exploited *on 32-bit kernels* by leaking 2^32
references to the same ring, because the file refcount is stored in a
pointer-sized field and get_file() doesn't have protection against
refcount overflow, just a WARN_ONCE(); but on 64-bit it should have no
impact beyond a memory leak.

Cc: stable@vger.kernel.org
Fixes: e7a6c00dc77a ("io_uring: add support for registering ring file descriptors")
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20241218-uring-reg-ring-cleanup-v1-1-8f63e999045b@google.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jann Horn 2024-12-18 17:56:25 +01:00 committed by Jens Axboe
parent 020b40f356
commit 12d908116f
2 changed files with 2 additions and 3 deletions
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4
include/linux/io_uring.h
View File

@ -15,10 +15,8 @@ bool io_is_uring_fops(struct file *file);
static inline void io_uring_files_cancel(void)
{
if (current->io_uring) {
io_uring_unreg_ringfd();
if (current->io_uring)
__io_uring_cancel(false);
}
}
static inline void io_uring_task_cancel(void)
{

1
io_uring/io_uring.c
View File

@ -3214,6 +3214,7 @@ end_wait:
void __io_uring_cancel(bool cancel_all)
{
io_uring_unreg_ringfd();
io_uring_cancel_generic(cancel_all, NULL);
}