From: Jann Horn Date: Wed, 18 Dec 2024 16:56:25 +0000 (+0100) Subject: io_uring: Fix registered ring file refcount leak X-Git-Tag: io_uring-6.13-20241220~2 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=12d908116f7efd34f255a482b9afc729d7a5fb78;p=linux-block.git 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: e7a6c00dc77a ("io_uring: add support for registering ring file descriptors") Signed-off-by: Jann Horn Link: https://lore.kernel.org/r/20241218-uring-reg-ring-cleanup-v1-1-8f63e999045b@google.com Signed-off-by: Jens Axboe --- diff --git a/include/linux/io_uring.h b/include/linux/io_uring.h index e123d5e17b52..85fe4e6b275c 100644 --- a/include/linux/io_uring.h +++ b/include/linux/io_uring.h @@ -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) { diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 605625e932eb..432b95ca9c85 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -3214,6 +3214,7 @@ end_wait: void __io_uring_cancel(bool cancel_all) { + io_uring_unreg_ringfd(); io_uring_cancel_generic(cancel_all, NULL); }