Re: KASAN reported an error while executing accept-reust.t testcase

[Jens Axboe <axboe@kernel.dk>]

On 1/11/25 7:07 AM, lizetao wrote:
> Hi all,
> 
> When I run the testcase liburing/accept-reust.t with CONFIG_KASAN=y and CONFIG_KASAN_EXTRA_INFO=y, I got
> a error reported by KASAN:

Looks more like you get KASAN crashing...

> Unable to handle kernel paging request at virtual address 00000c6455008008
> Mem abort info:
>   ESR = 0x0000000096000004
>   EC = 0x25: DABT (current EL), IL = 32 bits
>   SET = 0, FnV = 0
>   EA = 0, S1PTW = 0
>   FSC = 0x04: level 0 translation fault
> Data abort info:
>   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
>   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
>   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> user pgtable: 4k pages, 48-bit VAs, pgdp=00000001104c5000
> [00000c6455008008] pgd=0000000000000000, p4d=0000000000000000
> Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 6 UID: 0 PID: 352 Comm: kworker/u128:5 Not tainted 6.13.0-rc6-g0a2cb793507d #5
> Hardware name: linux,dummy-virt (DT)
> Workqueue: iou_exit io_ring_exit_work
> pstate: 10000005 (nzcV daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : __kasan_mempool_unpoison_object+0x38/0x170
> lr : io_netmsg_cache_free+0x8c/0x180
> sp : ffff800083297a90
> x29: ffff800083297a90 x28: ffffd4d7f67e88e4 x27: 0000000000000003
> x26: 1fffe5958011502e x25: ffff2cabff976c18 x24: 1fffe5957ff2ed83
> x23: ffff2cabff976c10 x22: 00000c6455008000 x21: 0002992540200001
> x20: 0000000000000000 x19: 00000c6455008000 x18: 00000000489683f8
> x17: ffffd4d7f68006ac x16: ffffd4d7f67eb3e0 x15: ffffd4d7f67e88e4
> x14: ffffd4d7f766deac x13: ffffd4d7f6619030 x12: ffff7a9b012e3e26
> x11: 1ffffa9b012e3e25 x10: ffff7a9b012e3e25 x9 : ffffd4d7f766debc
> x8 : ffffd4d80971f128 x7 : 0000000000000001 x6 : 00008564fed1c1db
> x5 : ffffd4d80971f128 x4 : ffff7a9b012e3e26 x3 : ffff2cabff976c00
> x2 : ffffc1ffc0000000 x1 : 0000000000000000 x0 : 0002992540200001
> Call trace:
>  __kasan_mempool_unpoison_object+0x38/0x170 (P)
>  io_netmsg_cache_free+0x8c/0x180
>  io_ring_exit_work+0xd4c/0x13a0
>  process_one_work+0x52c/0x1000
>  worker_thread+0x830/0xdc0
>  kthread+0x2bc/0x348
>  ret_from_fork+0x10/0x20
> Code: aa0003f5 aa0103f4 8b131853 aa1303f6 (f9400662) 
> ---[ end trace 0000000000000000 ]---
> 
> 
> I preliminary analyzed the accept and connect code logic. In the
> accept-reuse.t testcase, kmsg->free_iov is not used, so when calling
> io_netmsg_cache_free(), the
> kasan_mempool_unpoison_object(kmsg->free_iov...) path should not be
> executed.
> 
> 
> I used the hardware watchpoint to capture the first scene of modifying kmsg->free_iov:
> 
> Thread 3 hit Hardware watchpoint 7: *0xffff0000ebfc5410
> Old value = 0
> New value = -211812350
> kasan_set_track (stack=<optimized out>, track=<optimized out>) at ./arch/arm64/include/asm/current.h:21
> 21		return (struct task_struct *)sp_el0;
> 
> # bt
> kasan_set_track
> kasan_save_track
> kasan_save_free_info
> poison_slab_object
> __kasan_mempool_poison_object
> kasan_mempool_poison_object
> io_alloc_cache_put
> io_netmsg_recycle
> io_req_msg_cleanup
> io_connect
> io_issue_sqe
> io_queue_sqe
> io_req_task_submit
> ...
> 
> 
> It's a bit strange. It was modified by KASAN. I can't understand this.
> Maybe I missed something? Please let me know. Thanks.

Looks like KASAN with the extra info ends up writing to
io_async_msghdr->free_iov somehow. No idea... For the test case in
question, ->free_iov should be NULL when initially allocated, and the
io_uring code isn't storing to it. Yet it's non-NULL when you later go
and free it, after calling kasan_mempool_poison_object().

-- 
Jens Axboe