On Thu, Aug 30, 2018 at 2:52 AM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: >>>>> Hello, >>>>> >>>>> syzbot found the following crash on: >>>>> >>>>> HEAD commit: 5b394b2ddf03 Linux 4.19-rc1 >>>>> git tree: upstream >>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=14f4d8e1400000 >>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=49927b422dcf0b29 >>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=45a34334c61a8ecf661d >>>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13127e5a400000 >>>>> >>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>>>> Reported-by: syzbot+45a34334c61a8ecf661d@xxxxxxxxxxxxxxxxxxxxxxxxx >>>>> >>>>> IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready >>>>> IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready >>>>> IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready >>>>> 8021q: adding VLAN 0 to HW filter on device team0 >>>>> ================================================================== >>>>> BUG: KASAN: stack-out-of-bounds in schedule_debug kernel/sched/core.c:3285 >>>>> [inline] >>>>> BUG: KASAN: stack-out-of-bounds in __schedule+0x1977/0x1df0 >>>>> kernel/sched/core.c:3395 >>>>> Read of size 8 at addr ffff8801ad090000 by task syz-executor0/4718 >>>> >>>> Weird, can you please help me decipher this? So here KASAN complains about >>>> wrong memory access in the scheduler. >> >> This looks like a result of a previous bad silent memory corruption. >> >> The KASAN report says there is a stack out-of-bounds in scheduler. And >> that if followed by slab corruption report in another task. >> >> fs/jbd2/transaction.c happens to be the first meaningful file in this >> crash, and so that's where it is attributed to. >> >> Rerunning the reproducer several times can maybe give some better >> glues, or maybe not, maybe they all will look equally puzzling. >> >> This part of the repro looks familiar: >> >> r1 = bpf$MAP_CREATE(0x0, &(0x7f0000002e40)={0x12, 0x0, 0x4, 0x6e, 0x0, >> 0x1}, 0x68) >> bpf$MAP_UPDATE_ELEM(0x2, &(0x7f0000000180)={r1, &(0x7f0000000000), >> &(0x7f0000000140)}, 0x20) >> >> We had exactly such consequences of a bug in bpf map very recently, >> but that was claimed to be fixed. Maybe not completely? >> +bpf maintainers > > Looks like syzbot found this in Linus tree with HEAD commit 5b394b2ddf03 ("Linux 4.19-rc1") > one day later net PR got merged via 050cdc6c9501 ("Merge git://git.kernel.org/pub/..."). > > This PR contained a couple of fixes I did on sockmap code during audit such as: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b845c898b2f1ea458d5453f0fa1da6e2dfce3bb4 > > Looking at the reproducer syzkaller found it contains: > > r1 = bpf$MAP_CREATE(0x0, &(0x7f0000002e40)={0x12, 0x0, 0x4, 0x6e, 0x0, 0x1}, 0x68) > ^^^ > > So it found the crash with map type of sock hash and key size of 0x0 (which is invalid), > where subsequent map update triggered the corruption. I just did a 'syz test' and it > wasn't able to trigger the crash anymore. > > #syz fix: bpf, sockmap: fix sock_hash_alloc and reject zero-sized keys Thanks. I am again trying to figure out how/why this causes such bad failure modes. Looking at sock_hash_ctx_update_elem it seems that all of htab_map_hash/lookup_elem_raw/alloc_sock_hash_elem should handle key_size=0 fine hashing/comparing/updating 0 bytes. Do you have any ideas as to what could have gone wrong?
