Commit 12d90811 authored by Jann Horn's avatar Jann Horn Committed by Jens Axboe
Browse files

io_uring: Fix registered ring file refcount leak 



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: e7a6c00d ("io_uring: add support for registering ring file descriptors")
Signed-off-by: default avatarJann Horn <jannh@google.com>
Link: https://lore.kernel.org/r/20241218-uring-reg-ring-cleanup-v1-1-8f63e999045b@google.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 020b40f3

include/linux/io_uring.h

+1 −3
Original line number Diff line number Diff line
@@ -15,11 +15,9 @@ 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)

{

	if (current->io_uring)

io_uring/io_uring.c

+1 −0
Original line number Diff line number Diff line
@@ -3214,6 +3214,7 @@ __cold void io_uring_cancel_generic(bool cancel_all, struct io_sq_data *sqd) 


void __io_uring_cancel(bool cancel_all)

{

	io_uring_unreg_ringfd();

	io_uring_cancel_generic(cancel_all, NULL);

}