Subject: Re: KASAN: slab-out-of-bounds Read in __dev_queue_xmit

From: Eric Dumazet <[email-masked]>
Date: Thu, 18 Jan 2018 16:59:15 -0800

On Thu, 2018-01-18 at 15:58 -0800, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on linux-next commit
> 0e08c463db387a2adcb0243b15ab868a73f87807
> 
> So far this crash happened 6 times on linux-next, mmots, upstream.
> C reproducer is attached.
> syzkaller reproducer is attached.
> Raw console output is attached.
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: [email-masked]
> It will help syzbot understand when the bug is fixed. See footer for  
> details.
> If you forward the report, please keep this part and the footer.
> 
> device syz0 entered promiscuous mode
> audit: type=1400 audit(1514752309.665:10): avc:  denied  { net_raw } for   
> pid=3143 comm="syzkaller343753" capability=13   
> scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
> tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns  
> permissive=1
> audit: type=1400 audit(1514752309.668:11): avc:  denied  { net_admin } for   
> pid=3143 comm="syzkaller343753" capability=12   
> scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
> tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=cap_userns  
> permissive=1
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in __tcp_hdrlen include/linux/tcp.h:35  
> [inline]
> BUG: KASAN: slab-out-of-bounds in tcp_hdrlen include/linux/tcp.h:40 [inline]
> BUG: KASAN: slab-out-of-bounds in qdisc_pkt_len_init net/core/dev.c:3160  
> [inline]
> BUG: KASAN: slab-out-of-bounds in __dev_queue_xmit+0x20d3/0x2200  
> net/core/dev.c:3465
> Read of size 2 at addr ffff8801c85791e0 by task syzkaller343753/3143
> 
> CPU: 0 PID: 3143 Comm: syzkaller343753 Not tainted  
> 4.15.0-rc4-next-20171221+ #78
> 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+0x194/0x257 lib/dump_stack.c:53
>   print_address_description+0x73/0x250 mm/kasan/report.c:252
>   kasan_report_error mm/kasan/report.c:351 [inline]
>   kasan_report+0x25b/0x340 mm/kasan/report.c:409
>   __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:428
>   __tcp_hdrlen include/linux/tcp.h:35 [inline]
>   tcp_hdrlen include/linux/tcp.h:40 [inline]
>   qdisc_pkt_len_init net/core/dev.c:3160 [inline]
>   __dev_queue_xmit+0x20d3/0x2200 net/core/dev.c:3465
>   dev_queue_xmit+0x17/0x20 net/core/dev.c:3554
>   packet_snd net/packet/af_packet.c:2943 [inline]
>   packet_sendmsg+0x3ad5/0x60a0 net/packet/af_packet.c:2968
>   sock_sendmsg_nosec net/socket.c:628 [inline]
>   sock_sendmsg+0xca/0x110 net/socket.c:638
>   sock_write_iter+0x31a/0x5d0 net/socket.c:907
>   call_write_iter include/linux/fs.h:1776 [inline]
>   new_sync_write fs/read_write.c:469 [inline]
>   __vfs_write+0x684/0x970 fs/read_write.c:482
>   vfs_write+0x189/0x510 fs/read_write.c:544
>   SYSC_write fs/read_write.c:589 [inline]
>   SyS_write+0xef/0x220 fs/read_write.c:581
>   entry_SYSCALL_64_fastpath+0x1f/0x96
> RIP: 0033:0x444df9
> RSP: 002b:00000000007eff78 EFLAGS: 00000297 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007ffc3d2180f0 RCX: 0000000000444df9
> RDX: 00000000000000ce RSI: 0000000020fecf2b RDI: 0000000000000005
> RBP: 0000000000000000 R08: 0000000120080522 R09: 0000000120080522
> R10: 0000000120080522 R11: 0000000000000297 R12: 00000000004029f0
> R13: 0000000000402a80 R14: 0000000000000000 R15: 0000000000000000
> 
> Allocated by task 3143:
>   save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>   set_track mm/kasan/kasan.c:459 [inline]
>   kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>   __do_kmalloc_node mm/slab.c:3673 [inline]
>   __kmalloc_node_track_caller+0x47/0x70 mm/slab.c:3687
>   __kmalloc_reserve.isra.41+0x41/0xd0 net/core/skbuff.c:137
>   __alloc_skb+0x13b/0x780 net/core/skbuff.c:205
>   alloc_skb include/linux/skbuff.h:983 [inline]
>   alloc_skb_with_frags+0x10d/0x750 net/core/skbuff.c:5146
>   sock_alloc_send_pskb+0x787/0x9b0 net/core/sock.c:2088
>   packet_alloc_skb net/packet/af_packet.c:2802 [inline]
>   packet_snd net/packet/af_packet.c:2893 [inline]
>   packet_sendmsg+0x1ec2/0x60a0 net/packet/af_packet.c:2968
>   sock_sendmsg_nosec net/socket.c:628 [inline]
>   sock_sendmsg+0xca/0x110 net/socket.c:638
>   sock_write_iter+0x31a/0x5d0 net/socket.c:907
>   call_write_iter include/linux/fs.h:1776 [inline]
>   new_sync_write fs/read_write.c:469 [inline]
>   __vfs_write+0x684/0x970 fs/read_write.c:482
>   vfs_write+0x189/0x510 fs/read_write.c:544
>   SYSC_write fs/read_write.c:589 [inline]
>   SyS_write+0xef/0x220 fs/read_write.c:581
>   entry_SYSCALL_64_fastpath+0x1f/0x96
> 
> Freed by task 0:
> (stack is not available)
> 
> The buggy address belongs to the object at ffff8801c8578d80
>   which belongs to the cache kmalloc-1024 of size 1024
> The buggy address is located 96 bytes to the right of
>   1024-byte region [ffff8801c8578d80, ffff8801c8579180)
> The buggy address belongs to the page:
> page:00000000c294763f count:1 mapcount:0 mapping:0000000098a38184 index:0x0  
> compound_mapcount: 0
> flags: 0x2fffc0000008100(slab|head)
> raw: 02fffc0000008100 ffff8801c8578000 0000000000000000 0000000100000007
> raw: ffffea0007252920 ffff8801dac01848 ffff8801dac00ac0 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>   ffff8801c8579080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   ffff8801c8579100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > ffff8801c8579180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> 
>                                                         ^
>   ffff8801c8579200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8801c8579280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 
> 
> ---
> This bug is generated by a dumb bot. It may contain errors.
> See https://goo.gl/tpsmEJ for details.
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> 
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Sigh...

That has been discussed on netdev@ last days.

Fixes are in progress, first one being :

https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=d0c081b49137cd3200f2023c0875723be66e7ce5

Second one is not urgent, but will follow.