6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn <jannh@xxxxxxxxxx>
commit 12d908116f7efd34f255a482b9afc729d7a5fb78 upstream.
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@xxxxxxxxxxxxxxx
Fixes: e7a6c00dc77a ("io_uring: add support for registering ring file descriptors")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20241218-uring-reg-ring-cleanup-v1-1-8f63e999045b@xxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/io_uring.h | 4 +---
io_uring/io_uring.c | 1 +
2 files changed, 2 insertions(+), 3 deletions(-)
--- a/include/linux/io_uring.h
+++ b/include/linux/io_uring.h
@@ -65,10 +65,8 @@ static inline void io_uring_cmd_complete
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)
{
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3431,6 +3431,7 @@ end_wait:
void __io_uring_cancel(bool cancel_all)
{
+ io_uring_unreg_ringfd();
io_uring_cancel_generic(cancel_all, NULL);
}
