Messages in this thread | | | Date | Tue, 29 Aug 2023 14:29:56 -0400 | Subject | Re: [syzbot] [bpf?] KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update (2) | From | Yonghong Song <> |
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On 8/29/23 5:39 AM, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 727dbda16b83 Merge tag 'hardening-v6.6-rc1' of git://git.k.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=136f39dfa80000 > kernel config: https://syzkaller.appspot.com/x/.config?x=dea9c2ce3f646a25 > dashboard link: https://syzkaller.appspot.com/bug?extid=97522333291430dd277f > 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/9923a023ab11/disk-727dbda1.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/650dbc695d77/vmlinux-727dbda1.xz > kernel image: https://storage.googleapis.com/syzbot-assets/361da71276bf/bzImage-727dbda1.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+97522333291430dd277f@syzkaller.appspotmail.com > > ================================================================== > BUG: KCSAN: data-race in bpf_percpu_array_update / bpf_percpu_array_update > > write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1: > bpf_long_memcpy include/linux/bpf.h:428 [inline] > bpf_obj_memcpy include/linux/bpf.h:441 [inline] > copy_map_value_long include/linux/bpf.h:464 [inline] > bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380 > bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175 > generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749 > bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648 > __sys_bpf+0x28a/0x780 > __do_sys_bpf kernel/bpf/syscall.c:5241 [inline] > __se_sys_bpf kernel/bpf/syscall.c:5239 [inline] > __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0: > bpf_long_memcpy include/linux/bpf.h:428 [inline] > bpf_obj_memcpy include/linux/bpf.h:441 [inline] > copy_map_value_long include/linux/bpf.h:464 [inline] > bpf_percpu_array_update+0x3bb/0x500 kernel/bpf/arraymap.c:380 > bpf_map_update_value+0x190/0x370 kernel/bpf/syscall.c:175 > generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1749 > bpf_map_do_batch+0x2df/0x3d0 kernel/bpf/syscall.c:4648 > __sys_bpf+0x28a/0x780 > __do_sys_bpf kernel/bpf/syscall.c:5241 [inline] > __se_sys_bpf kernel/bpf/syscall.c:5239 [inline] > __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5239 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > value changed: 0x0000000000000000 -> 0xfffffff000002788 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 0 PID: 8268 Comm: syz-executor.4 Not tainted 6.5.0-syzkaller-00453-g727dbda16b83 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023 > ==================================================================
This case is with two tasks doing bpf_map batch update together for the same map and key. > write to 0xffffe8fffe7425d8 of 8 bytes by task 8257 on cpu 1: > write to 0xffffe8fffe7425d8 of 8 bytes by task 8268 on cpu 0:
So concurrency is introduced by user applications. In my opinion, this probably not an issue from kernel perspective.
> > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@googlegroups.com. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the bug is already fixed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite bug's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the bug is a duplicate of another bug, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup >
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