Re: [syzbot] BUG: unable to handle kernel paging request in percpu_counter_add_batch

[Andrew Morton]

On Thu, 20 Oct 2022 19:24:40 -0700 syzbot <syzbot+96e659d35b9d6b541152@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    aae703b02f92 Merge tag 'for-6.1-rc1-tag' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1686e478880000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=883de36878e6d869
> dashboard link: https://syzkaller.appspot.com/bug?extid=96e659d35b9d6b541152
> compiler:       aarch64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: arm
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+96e659d35b9d6b541152@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> Unable to handle kernel paging request at virtual address ffff70000b978a00
> KASAN: maybe wild-memory-access in range [0xffff80005cbc5000-0xffff80005cbc5007]
> Mem abort info:
>   ESR = 0x0000000096000006
>   EC = 0x25: DABT (current EL), IL = 32 bits
>   SET = 0, FnV = 0
>   EA = 0, S1PTW = 0
>   FSC = 0x06: level 2 translation fault
> Data abort info:
>   ISV = 0, ISS = 0x00000006
>   CM = 0, WnR = 0
> swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000045dfb000
> [ffff70000b978a00] pgd=00000000bfbeb003, p4d=00000000bfbeb003, pud=00000000bfbea003, pmd=0000000000000000
> Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 0 PID: 2820 Comm: kworker/0:3 Tainted: G        W          6.1.0-rc1-syzkaller-00025-gaae703b02f92 #0
> Hardware name: linux,dummy-virt (DT)
> Workqueue: events free_ipc
> pstate: 10000005 (nzcV daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : percpu_counter_add_batch+0x78/0x2f0 lib/percpu_counter.c:87
> lr : percpu_counter_add_batch+0x44/0x2f0 lib/percpu_counter.c:87
> sp : ffff8000120979c0
> x29: ffff8000120979c0 x28: ffff0000151ff800 x27: 1fffe00002a3ff24
> x26: ffff80005cbc5000 x25: ffff00000eeac7b0 x24: 1fffe00001dd58f6
> x23: 000000007fffffff x22: ffff80000cc4e800 x21: 0000000000000000
> x20: 0000000000000000 x19: ffff00000eeac758 x18: ffff00006a9cbbc0
> x17: 0000000000000000 x16: 0000000000000000 x15: ffff800008d9c830
> x14: ffff800008d78ecc x13: ffff800008d752d4 x12: ffff600002a3ff01
> x11: 1fffe00002a3ff00 x10: ffff600002a3ff00 x9 : dfff800000000000
> x8 : ffff0000151ff800 x7 : 00000000f1f1f1f1 x6 : dfff800000000000
> x5 : ffff700002412f32 x4 : 1ffff000020ef1ac x3 : 1ffff0000b978a00
> x2 : dfff800000000000 x1 : 0000000000000003 x0 : ffff80005cbc5000
> Call trace:
>  percpu_counter_add_batch+0x78/0x2f0 lib/percpu_counter.c:87
>  percpu_counter_add_local include/linux/percpu_counter.h:75 [inline]
>  percpu_counter_sub_local include/linux/percpu_counter.h:225 [inline]
>  freeque+0x20c/0x364 ipc/msg.c:292
>  free_ipcs+0xa0/0x160 ipc/namespace.c:125
>  msg_exit_ns+0x38/0x60 ipc/msg.c:1334
>  free_ipc_ns ipc/namespace.c:138 [inline]
>  free_ipc+0xd0/0x1c0 ipc/namespace.c:157
>  process_one_work+0x780/0x184c kernel/workqueue.c:2289
>  worker_thread+0x3cc/0xc40 kernel/workqueue.c:2436
>  kthread+0x23c/0x2a0 kernel/kthread.c:376
>  ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860

Well.  freeque() messes with ns->percpu_msg_hdrs but msg_exit_ns()
already did percpu_counter_destroy(&ns->percpu_msg_hdrs);

I'm thinking something like this?

--- a/ipc/msg.c~a
+++ a/ipc/msg.c
@@ -1329,11 +1329,11 @@ fail_msg_bytes:
 #ifdef CONFIG_IPC_NS
 void msg_exit_ns(struct ipc_namespace *ns)
 {
-	percpu_counter_destroy(&ns->percpu_msg_bytes);
-	percpu_counter_destroy(&ns->percpu_msg_hdrs);
 	free_ipcs(ns, &msg_ids(ns), freeque);
 	idr_destroy(&ns->ids[IPC_MSG_IDS].ipcs_idr);
 	rhashtable_destroy(&ns->ids[IPC_MSG_IDS].key_ht);
+	percpu_counter_destroy(&ns->percpu_msg_bytes);
+	percpu_counter_destroy(&ns->percpu_msg_hdrs);
 }
 #endif
 
_