Re: [syzbot] [mm?] UBSAN: shift-out-of-bounds in do_shrink_slab

[Qi Zheng <arch0.zheng@gmail.com>]

Hi,

I think this bug was introduced by commit 6be5e186fd65
("mm: vmscan: restore incremental cgroup iteration"), and
can be fixed by commit 9c8805439853 ("mm: vmscan: reset sc->priority on 
retry").

Thanks,
Qi


On 2024/6/1 15:08, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    6dc544b66971 Add linux-next specific files for 20240528
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14c7f806980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6a363b35598e573d
> dashboard link: https://syzkaller.appspot.com/bug?extid=981b8efffb3d71c46bef
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/334699ab67f8/disk-6dc544b6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/4ca32b2218ce/vmlinux-6dc544b6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/400bc5f019b3/bzImage-6dc544b6.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+981b8efffb3d71c46bef@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> UBSAN: shift-out-of-bounds in mm/shrinker.c:406:18
> shift exponent -1 is negative
> CPU: 0 PID: 5278 Comm: syz-executor.1 Not tainted 6.10.0-rc1-next-20240528-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:88 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
>   ubsan_epilogue lib/ubsan.c:231 [inline]
>   __ubsan_handle_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
>   do_shrink_slab+0xe26/0x1160 mm/shrinker.c:406
>   shrink_slab_memcg mm/shrinker.c:548 [inline]
>   shrink_slab+0x87c/0x14d0 mm/shrinker.c:626
>   shrink_node_memcgs mm/vmscan.c:5923 [inline]
>   shrink_node+0xb82/0x4150 mm/vmscan.c:5961
>   shrink_zones mm/vmscan.c:6205 [inline]
>   do_try_to_free_pages+0x789/0x1cb0 mm/vmscan.c:6267
>   try_to_free_mem_cgroup_pages+0x48f/0xb10 mm/vmscan.c:6598
>   try_charge_memcg+0x704/0x1850 mm/memcontrol.c:2946
>   obj_cgroup_charge_pages mm/memcontrol.c:3420 [inline]
>   __memcg_kmem_charge_page+0xe2/0x250 mm/memcontrol.c:3446
>   __alloc_pages_noprof+0x28c/0x6c0 mm/page_alloc.c:4712
>   __alloc_pages_node_noprof include/linux/gfp.h:269 [inline]
>   alloc_pages_node_noprof include/linux/gfp.h:296 [inline]
>   bpf_ringbuf_area_alloc kernel/bpf/ringbuf.c:122 [inline]
>   bpf_ringbuf_alloc+0xcb/0x420 kernel/bpf/ringbuf.c:170
>   ringbuf_map_alloc+0x1d7/0x2f0 kernel/bpf/ringbuf.c:204
>   map_create+0x90c/0x1200 kernel/bpf/syscall.c:1333
>   __sys_bpf+0x6d1/0x810 kernel/bpf/syscall.c:5669
>   __do_sys_bpf kernel/bpf/syscall.c:5794 [inline]
>   __se_sys_bpf kernel/bpf/syscall.c:5792 [inline]
>   __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5792
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7efea107cee9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007efea1de60c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 00007efea11b3fa0 RCX: 00007efea107cee9
> RDX: 0000000000000048 RSI: 00000000200002c0 RDI: 0000000000000000
> RBP: 00007efea10c947f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007efea11b3fa0 R15: 00007fff6651b5d8
>   </TASK>
> ---[ end trace ]---
> 
> 
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