Messages in this thread | | | From | Alexander Potapenko <> | Date | Wed, 12 Sep 2018 12:38:25 +0200 | Subject | Re: KMSAN: uninit-value in pppoe_rcv |
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On Wed, Sep 12, 2018 at 12:24 PM syzbot <syzbot+f5f6080811c849739212@syzkaller.appspotmail.com> wrote: > > Hello, > > syzbot found the following crash on: > > HEAD commit: d2d741e5d189 kmsan: add initialization for shmem pages > git tree: https://github.com/google/kmsan.git/master > console output: https://syzkaller.appspot.com/x/log.txt?x=1465fc37800000 > kernel config: https://syzkaller.appspot.com/x/.config?x=48f9de3384bcd0f > dashboard link: https://syzkaller.appspot.com/bug?extid=f5f6080811c849739212 > compiler: clang version 7.0.0 (trunk 329391) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14d6e607800000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10a15b5b800000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+f5f6080811c849739212@syzkaller.appspotmail.com > > IPVS: ftp: loaded support on port[0] = 21 > ================================================================== > BUG: KMSAN: uninit-value in __get_item drivers/net/ppp/pppoe.c:172 [inline] > BUG: KMSAN: uninit-value in get_item drivers/net/ppp/pppoe.c:236 [inline] > BUG: KMSAN: uninit-value in pppoe_rcv+0xcef/0x10e0 > drivers/net/ppp/pppoe.c:450 > CPU: 0 PID: 4543 Comm: syz-executor355 Not tainted 4.16.0+ #87 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:17 [inline] > dump_stack+0x185/0x1d0 lib/dump_stack.c:53 > kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067 > __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683 > __get_item drivers/net/ppp/pppoe.c:172 [inline] > get_item drivers/net/ppp/pppoe.c:236 [inline] > pppoe_rcv+0xcef/0x10e0 drivers/net/ppp/pppoe.c:450 > __netif_receive_skb_core+0x47df/0x4a90 net/core/dev.c:4562 > __netif_receive_skb net/core/dev.c:4627 [inline] > netif_receive_skb_internal+0x49d/0x630 net/core/dev.c:4701 > netif_receive_skb+0x230/0x240 net/core/dev.c:4725 > tun_rx_batched drivers/net/tun.c:1555 [inline] > tun_get_user+0x740f/0x7c60 drivers/net/tun.c:1962 > tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1990 > call_write_iter include/linux/fs.h:1782 [inline] > new_sync_write fs/read_write.c:469 [inline] > __vfs_write+0x7fb/0x9f0 fs/read_write.c:482 > vfs_write+0x463/0x8d0 fs/read_write.c:544 > SYSC_write+0x172/0x360 fs/read_write.c:589 > SyS_write+0x55/0x80 fs/read_write.c:581 > do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287 > entry_SYSCALL_64_after_hwframe+0x3d/0xa2 > RIP: 0033:0x4447c9 > RSP: 002b:00007fff64c8fc28 EFLAGS: 00000297 ORIG_RAX: 0000000000000001 > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004447c9 > RDX: 000000000000fd87 RSI: 0000000020000600 RDI: 0000000000000004 > RBP: 00000000006cf018 R08: 00007fff64c8fda8 R09: 00007fff00006bda > R10: 0000000000005fe7 R11: 0000000000000297 R12: 00000000004020d0 > R13: 0000000000402160 R14: 0000000000000000 R15: 0000000000000000 > > Uninit was created at: > kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline] > kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188 > kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314 > kmsan_slab_alloc+0x11/0x20 mm/kmsan/kmsan.c:321 > slab_post_alloc_hook mm/slab.h:445 [inline] > slab_alloc_node mm/slub.c:2737 [inline] > __kmalloc_node_track_caller+0xaed/0x11c0 mm/slub.c:4369 > __kmalloc_reserve net/core/skbuff.c:138 [inline] > __alloc_skb+0x2cf/0x9f0 net/core/skbuff.c:206 > alloc_skb include/linux/skbuff.h:984 [inline] > alloc_skb_with_frags+0x1d4/0xb20 net/core/skbuff.c:5234 > sock_alloc_send_pskb+0xb56/0x1190 net/core/sock.c:2085 > tun_alloc_skb drivers/net/tun.c:1532 [inline] > tun_get_user+0x2242/0x7c60 drivers/net/tun.c:1829 > tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1990 > call_write_iter include/linux/fs.h:1782 [inline] > new_sync_write fs/read_write.c:469 [inline] > __vfs_write+0x7fb/0x9f0 fs/read_write.c:482 > vfs_write+0x463/0x8d0 fs/read_write.c:544 > SYSC_write+0x172/0x360 fs/read_write.c:589 > SyS_write+0x55/0x80 fs/read_write.c:581 > do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287 > entry_SYSCALL_64_after_hwframe+0x3d/0xa2 > ================================================================== I did a little digging before sending the bug upstream. If I add memset(obj, 0xfe, size) to __kmalloc_reserve(), these 0xfe bytes are visible in __get_item() at the place where KMSAN reports an error.
The problem is somehow related to tun_get_user() creating a fragmented sk_buff - when I change the call to tun_alloc_skb() so that it allocates a single buffer the bug goes away.
> > --- > This bug 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 bug report. See: > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with > syzbot. > syzbot can test patches for this bug, for details see: > https://goo.gl/tpsmEJ#testing-patches > > -- > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/0000000000004624c30575a9fd40%40google.com. > For more options, visit https://groups.google.com/d/optout.
-- Alexander Potapenko Software Engineer
Google Germany GmbH Erika-Mann-Straße, 33 80636 München
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