KASAN: slab-out-of-bounds Read in bpf_skb_change_proto

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 84ae3e35 Merge 4.14.73 into android-4.14
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=1089b0e9400000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b3b342f97278cde
dashboard link: https://syzkaller.appspot.com/bug?extid=31bfca20270b24afafc0
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11d3627e400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13f70756400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+31bfca...@syzkaller.appspotmail.com

urandom_read: 1 callbacks suppressed
random: sshd: uninitialized urandom read (32 bytes read)
audit: type=1400 audit(1538400124.886:7): avc: denied { map } for
pid=1779 comm="syz-executor273" path="/root/syz-executor273583137"
dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
audit: type=1400 audit(1538400125.146:8): avc: denied { prog_load } for
pid=1780 comm="syz-executor273"
scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=bpf
permissive=1
==================================================================
BUG: KASAN: slab-out-of-bounds in bpf_skb_proto_xlat net/core/filter.c:2150
[inline]
BUG: KASAN: slab-out-of-bounds in ____bpf_skb_change_proto
net/core/filter.c:2188 [inline]
BUG: KASAN: slab-out-of-bounds in bpf_skb_change_proto+0xd7d/0x1100
net/core/filter.c:2163
Read of size 2 at addr ffff8801cc934b38 by task syz-executor273/1780

CPU: 1 PID: 1780 Comm: syz-executor273 Not tainted 4.14.73+ #12
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x11b lib/dump_stack.c:53
print_address_description+0x60/0x22b mm/kasan/report.c:252
kasan_report_error mm/kasan/report.c:351 [inline]
kasan_report.cold.6+0x11b/0x2dd mm/kasan/report.c:409
bpf_skb_proto_xlat net/core/filter.c:2150 [inline]
____bpf_skb_change_proto net/core/filter.c:2188 [inline]
bpf_skb_change_proto+0xd7d/0x1100 net/core/filter.c:2163
___bpf_prog_run+0x248e/0x5c70 kernel/bpf/core.c:1012

Allocated by task 227:
save_stack mm/kasan/kasan.c:447 [inline]
set_track mm/kasan/kasan.c:459 [inline]
kasan_kmalloc.part.1+0x4f/0xd0 mm/kasan/kasan.c:551
slab_post_alloc_hook mm/slab.h:442 [inline]
slab_alloc_node mm/slub.c:2723 [inline]
slab_alloc mm/slub.c:2731 [inline]
kmem_cache_alloc+0xe4/0x2b0 mm/slub.c:2736
kmem_cache_alloc_node include/linux/slab.h:361 [inline]
__alloc_skb+0xd8/0x550 net/core/skbuff.c:193
alloc_skb include/linux/skbuff.h:980 [inline]
alloc_skb_with_frags+0xab/0x500 net/core/skbuff.c:5167
sock_alloc_send_pskb+0x55e/0x6e0 net/core/sock.c:2075
unix_dgram_sendmsg+0x37b/0xf50 net/unix/af_unix.c:1681
sock_sendmsg_nosec net/socket.c:645 [inline]
sock_sendmsg+0xb5/0x100 net/socket.c:655
SYSC_sendto net/socket.c:1762 [inline]
SyS_sendto+0x211/0x340 net/socket.c:1730
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 191:
save_stack mm/kasan/kasan.c:447 [inline]
set_track mm/kasan/kasan.c:459 [inline]
kasan_slab_free+0xac/0x190 mm/kasan/kasan.c:524
slab_free_hook mm/slub.c:1389 [inline]
slab_free_freelist_hook mm/slub.c:1410 [inline]
slab_free mm/slub.c:2966 [inline]
kmem_cache_free+0x12d/0x350 mm/slub.c:2988
kfree_skbmem+0x9e/0x100 net/core/skbuff.c:582
__kfree_skb net/core/skbuff.c:642 [inline]
consume_skb+0xc9/0x330 net/core/skbuff.c:701
skb_free_datagram+0x15/0xd0 net/core/datagram.c:331
unix_dgram_recvmsg+0x762/0xd20 net/unix/af_unix.c:2183
sock_recvmsg_nosec net/socket.c:818 [inline]
sock_recvmsg+0xc0/0x100 net/socket.c:825
SYSC_recvfrom net/socket.c:1814 [inline]
SyS_recvfrom+0x1d2/0x310 net/socket.c:1786
do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
entry_SYSCALL_64_after_hwframe+0x42/0xb7

The buggy address belongs to the object at ffff8801cc934a00
which belongs to the cache skbuff_head_cache of size 224
The buggy address is located 88 bytes to the right of
224-byte region [ffff8801cc934a00, ffff8801cc934ae0)
The buggy address belongs to the page:
page:ffffea0007324d00 count:1 mapcount:0 mapping: (null) index:0x0
flags: 0x4000000000000100(slab)
raw: 4000000000000100 0000000000000000 0000000000000000 00000001800c000c
raw: 0000000000000000 0000000100000001 ffff8801d6770200 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801cc934a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801cc934a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ffff8801cc934b00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff8801cc934b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801cc934c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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