net: use after free in ip6_make_skb

[Sasha Levin]

Hi,

Fuzzing with syzkaller on the latest -next kernel produced this error:

[ 891.389013] ==================================================================

[ 891.390006] BUG: KASAN: use-after-free in ip6_make_skb+0x106/0x3d0 at addr ffff8806e9773a34

[ 891.393459] Read of size 2 by task syzkaller_execu/8350

[ 891.394128] =============================================================================

[ 891.395121] BUG kmalloc-64 (Not tainted): kasan: bad access detected

[ 891.395886] -----------------------------------------------------------------------------

[ 891.395886]

[ 891.398479] Disabling lock debugging due to kernel taint

[ 891.399156] INFO: Allocated in p9pdu_vreadf+0x7d4/0x1da0 age=2 cpu=12 pid=8331

[ 891.400255] ___slab_alloc+0x434/0x5b0

[ 891.400917] __slab_alloc.isra.37+0x79/0xd0

[ 891.401642] __kmalloc+0x12f/0x390

[ 891.402172] pipe_fcntl+0x195/0x4c0

[ 891.402743] SyS_fcntl+0xd70/0xe50

[ 891.403162] entry_SYSCALL_64_fastpath+0x35/0x9e

[ 891.403715] INFO: Freed in kfree_put_link+0x1a/0x20 age=6 cpu=12 pid=8331

[ 891.404349] __slab_free+0x5c/0x2b0

[ 891.404665] kfree+0x281/0x2f0

[ 891.404915] kfree_put_link+0x1a/0x20

[ 891.405201] path_openat+0x391f/0x5040

[ 891.405508] do_filp_open+0x1b8/0x250

[ 891.405814] do_open_execat+0x105/0x4d0

[ 891.406295] open_exec+0x3b/0x60

[ 891.406802] INFO: Slab 0xffffea001ba5dc00 objects=41 used=20 fp=0xffff8806e9773a30 flags=0x2fffff80004080

[ 891.407978] INFO: Object 0xffff8806e9773a30 @offset=14896 fp=0xffff8806e9772028

[ 891.407978]

[ 891.408888] Bytes b4 ffff8806e9773a20: e3 07 05 00 01 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ

[ 891.410121] Object ffff8806e9773a30: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk

[ 891.411425] Object ffff8806e9773a40: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk

[ 891.412603] Object ffff8806e9773a50: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk

[ 891.413775] Object ffff8806e9773a60: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.

[ 891.414977] Redzone ffff8806e9773a70: bb bb bb bb bb bb bb bb ........

[ 891.416092] Padding ffff8806e9773bb0: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ

[ 891.417221] CPU: 7 PID: 8350 Comm: syzkaller_execu Tainted: G B 4.4.0-rc2-next-20151126-sasha-00007-g7083bec-dirty #2655

[ 891.424771] Call Trace:

[ 891.425454] dump_stack (lib/dump_stack.c:52)
[ 891.426433] print_trailer (mm/slub.c:655)
[ 891.427482] object_err (mm/slub.c:662)
[ 891.428495] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236)
[ 891.430825] __asan_report_load2_noabort (mm/kasan/report.c:278)
[ 891.432908] ip6_make_skb (net/ipv6/ip6_output.c:1757)
[ 891.446294] udpv6_sendmsg (include/linux/err.h:40 net/ipv6/udp.c:1319)
[ 891.461731] inet_sendmsg (net/ipv4/af_inet.c:733)
[ 891.465359] sock_sendmsg (net/socket.c:611 net/socket.c:620)
[ 891.466211] sock_write_iter (net/socket.c:820)
[ 891.470869] __vfs_write (fs/read_write.c:480 fs/read_write.c:492)
[ 891.473525] vfs_write (fs/read_write.c:540)
[ 891.474341] SyS_write (fs/read_write.c:587 fs/read_write.c:578)
[ 891.477995] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188)
[ 891.478975] Memory state around the buggy address:

[ 891.479722] ffff8806e9773900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

[ 891.480830] ffff8806e9773980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

[ 891.481954] >ffff8806e9773a00: fc fc fc fc fc fc 00 00 00 00 00 00 00 fc fc fc

[ 891.483025] ^

[ 891.483622] ffff8806e9773a80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

[ 891.484469] ffff8806e9773b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

[ 891.485307] ==================================================================


Thanks,
Sasha

[Eric Dumazet]

Very similar to a report sent earlier by Dmitry.

Bug probably added by :

commit 03485f2adcde0c2d4e9228b659be78e872486bbb
Author: Vlad Yasevich <vyas...@gmail.com>
Date: Sat Jan 31 10:40:17 2015 -0500

udpv6: Add lockless sendmsg() support

This commit adds the same functionaliy to IPv6 that
commit 903ab86d195cca295379699299c5fc10beba31c7
Author: Herbert Xu <her...@gondor.apana.org.au>
Date: Tue Mar 1 02:36:48 2011 +0000

udp: Add lockless transmit path

added to IPv4.

UDP transmit path can now run without a socket lock,
thus allowing multiple threads to send to a single socket
more efficiently.
This is only used when corking/MSG_MORE is not used.

Signed-off-by: Vladislav Yasevich <vyas...@redhat.com>
Signed-off-by: David S. Miller <da...@davemloft.net>