On Tue, 29 Aug 2023 at 20:30, Yonghong Song <yonghong.song@xxxxxxxxx> wrote: > > > > 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ================================================================== > > 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. Perhaps not, but I recall there being a discussion about making KCSAN aware of memory accesses done by BPF programs (memcpy being a tiny subset of those). Not sure if the above data race qualifies as something we might want to still detect, i.e. a kernel dev testing their kernel might be interested in such a report. Regardless, in this case we should teach syzkaller to ignore KCSAN data races that originate from bpf user operations whatever the origin.
