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authorGabriel Krisman Bertazi <krisman@suse.de>2023-08-28 19:42:49 -0400
committerJens Axboe <axboe@kernel.dk>2023-08-30 09:53:44 -0600
commitbd6fc5da4c51107e1e0cec4a3a07963d1dae2c84 (patch)
treea62596652612da149c8d8b04834ca0bcfb5b07ac /io_uring
parent6c1b980a7e79e55e951b4b2c47eefebc75071209 (diff)
io_uring: Don't set affinity on a dying sqpoll thread
Syzbot reported a null-ptr-deref of sqd->thread inside io_sqpoll_wq_cpu_affinity. It turns out the sqd->thread can go away from under us during io_uring_register, in case the process gets a fatal signal during io_uring_register. It is not particularly hard to hit the race, and while I am not sure this is the exact case hit by syzbot, it solves it. Finally, checking ->thread is enough to close the race because we locked sqd while "parking" the thread, thus preventing it from going away. I reproduced it fairly consistently with a program that does: int main(void) { ... io_uring_queue_init(RING_LEN, &ring1, IORING_SETUP_SQPOLL); while (1) { io_uring_register_iowq_aff(ring, 1, &mask); } } Executed in a loop with timeout to trigger SIGTERM: while true; do timeout 1 /a.out ; done This will hit the following BUG() in very few attempts. BUG: kernel NULL pointer dereference, address: 00000000000007a8 PGD 800000010e949067 P4D 800000010e949067 PUD 10e46e067 PMD 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 0 PID: 15715 Comm: dead-sqpoll Not tainted 6.5.0-rc7-next-20230825-g193296236fa0-dirty #23 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:io_sqpoll_wq_cpu_affinity+0x27/0x70 Code: 90 90 90 0f 1f 44 00 00 55 53 48 8b 9f 98 03 00 00 48 85 db 74 4f 48 89 df 48 89 f5 e8 e2 f8 ff ff 48 8b 43 38 48 85 c0 74 22 <48> 8b b8 a8 07 00 00 48 89 ee e8 ba b1 00 00 48 89 df 89 c5 e8 70 RSP: 0018:ffffb04040ea7e70 EFLAGS: 00010282 RAX: 0000000000000000 RBX: ffff93c010749e40 RCX: 0000000000000001 RDX: 0000000000000000 RSI: ffffffffa7653331 RDI: 00000000ffffffff RBP: ffffb04040ea7eb8 R08: 0000000000000000 R09: c0000000ffffdfff R10: ffff93c01141b600 R11: ffffb04040ea7d18 R12: ffff93c00ea74840 R13: 0000000000000011 R14: 0000000000000000 R15: ffff93c00ea74800 FS: 00007fb7c276ab80(0000) GS:ffff93c36f200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000000007a8 CR3: 0000000111634003 CR4: 0000000000370ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> ? __die_body+0x1a/0x60 ? page_fault_oops+0x154/0x440 ? do_user_addr_fault+0x174/0x7b0 ? exc_page_fault+0x63/0x140 ? asm_exc_page_fault+0x22/0x30 ? io_sqpoll_wq_cpu_affinity+0x27/0x70 __io_register_iowq_aff+0x2b/0x60 __io_uring_register+0x614/0xa70 __x64_sys_io_uring_register+0xaa/0x1a0 do_syscall_64+0x3a/0x90 entry_SYSCALL_64_after_hwframe+0x6e/0xd8 RIP: 0033:0x7fb7c226fec9 Code: 2e 00 b8 ca 00 00 00 0f 05 eb a5 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 97 7f 2d 00 f7 d8 64 89 01 48 RSP: 002b:00007ffe2c0674f8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb7c226fec9 RDX: 00007ffe2c067530 RSI: 0000000000000011 RDI: 0000000000000003 RBP: 00007ffe2c0675d0 R08: 00007ffe2c067550 R09: 00007ffe2c067550 R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffe2c067750 R14: 0000000000000000 R15: 0000000000000000 </TASK> Modules linked in: CR2: 00000000000007a8 ---[ end trace 0000000000000000 ]--- Reported-by: syzbot+c74fea926a78b8a91042@syzkaller.appspotmail.com Fixes: ebdfefc09c6d ("io_uring/sqpoll: fix io-wq affinity when IORING_SETUP_SQPOLL is used") Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de> Link: https://lore.kernel.org/r/87v8cybuo6.fsf@suse.de Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'io_uring')
-rw-r--r--io_uring/sqpoll.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index ee2d2c687fda..bd6c2c7959a5 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -430,7 +430,9 @@ __cold int io_sqpoll_wq_cpu_affinity(struct io_ring_ctx *ctx,
if (sqd) {
io_sq_thread_park(sqd);
- ret = io_wq_cpu_affinity(sqd->thread->io_uring, mask);
+ /* Don't set affinity for a dying thread */
+ if (sqd->thread)
+ ret = io_wq_cpu_affinity(sqd->thread->io_uring, mask);
io_sq_thread_unpark(sqd);
}