6.12-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe axboe@kernel.dk
Commit fc582cd26e888b0652bc1494f252329453fd3b23 upstream.
syzbot reports that defer/local task_work adding via msg_ring can hit a request that has been freed:
CPU: 1 UID: 0 PID: 19356 Comm: iou-wrk-19354 Not tainted 6.16.0-rc4-syzkaller-00108-g17bbde2e1716 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call Trace: <TASK> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xd2/0x2b0 mm/kasan/report.c:521 kasan_report+0x118/0x150 mm/kasan/report.c:634 io_req_local_work_add io_uring/io_uring.c:1184 [inline] __io_req_task_work_add+0x589/0x950 io_uring/io_uring.c:1252 io_msg_remote_post io_uring/msg_ring.c:103 [inline] io_msg_data_remote io_uring/msg_ring.c:133 [inline] __io_msg_ring_data+0x820/0xaa0 io_uring/msg_ring.c:151 io_msg_ring_data io_uring/msg_ring.c:173 [inline] io_msg_ring+0x134/0xa00 io_uring/msg_ring.c:314 __io_issue_sqe+0x17e/0x4b0 io_uring/io_uring.c:1739 io_issue_sqe+0x165/0xfd0 io_uring/io_uring.c:1762 io_wq_submit_work+0x6e9/0xb90 io_uring/io_uring.c:1874 io_worker_handle_work+0x7cd/0x1180 io_uring/io-wq.c:642 io_wq_worker+0x42f/0xeb0 io_uring/io-wq.c:696 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK>
which is supposed to be safe with how requests are allocated. But msg ring requests alloc and free on their own, and hence must defer freeing to a sane time.
Add an rcu_head and use kfree_rcu() in both spots where requests are freed. Only the one in io_msg_tw_complete() is strictly required as it has been visible on the other ring, but use it consistently in the other spot as well.
This should not cause any other issues outside of KASAN rightfully complaining about it.
Link: https://lore.kernel.org/io-uring/686cd2ea.a00a0220.338033.0007.GAE@google.co... Reported-by: syzbot+54cbbfb4db9145d26fc2@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Fixes: 0617bb500bfa ("io_uring/msg_ring: improve handling of target CQE posting") Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit fc582cd26e888b0652bc1494f252329453fd3b23) Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/io_uring_types.h | 12 ++++++++++-- io_uring/msg_ring.c | 4 ++-- 2 files changed, 12 insertions(+), 4 deletions(-)
--- a/include/linux/io_uring_types.h +++ b/include/linux/io_uring_types.h @@ -646,8 +646,16 @@ struct io_kiocb { atomic_t refs; bool cancel_seq_set; struct io_task_work io_task_work; - /* for polled requests, i.e. IORING_OP_POLL_ADD and async armed poll */ - struct hlist_node hash_node; + union { + /* + * for polled requests, i.e. IORING_OP_POLL_ADD and async armed + * poll + */ + struct hlist_node hash_node; + + /* for private io_kiocb freeing */ + struct rcu_head rcu_head; + }; /* internal polling, see IORING_FEAT_FAST_POLL */ struct async_poll *apoll; /* opcode allocated if it needs to store data for async defer */ --- a/io_uring/msg_ring.c +++ b/io_uring/msg_ring.c @@ -82,7 +82,7 @@ static void io_msg_tw_complete(struct io spin_unlock(&ctx->msg_lock); } if (req) - kmem_cache_free(req_cachep, req); + kfree_rcu(req, rcu_head); percpu_ref_put(&ctx->refs); }
@@ -91,7 +91,7 @@ static int io_msg_remote_post(struct io_ { req->task = READ_ONCE(ctx->submitter_task); if (!req->task) { - kmem_cache_free(req_cachep, req); + kfree_rcu(req, rcu_head); return -EOWNERDEAD; } req->opcode = IORING_OP_NOP;