Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

On commit d3b5d35290d729a2518af00feca867385a1b08fa (4.11).

A reproducer and .config are attached.

==================================================================
BUG: KASAN: slab-out-of-bounds in pfkey_compile_policy+0x8e6/0xd40 at
addr ffff88006701f798
Read of size 1280 by task a.out/4181
CPU: 0 PID: 4181 Comm: a.out Not tainted 4.11.0+ #306
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16
 dump_stack+0x292/0x395 lib/dump_stack.c:52
 kasan_object_err+0x1c/0x70 mm/kasan/report.c:164
 print_address_description mm/kasan/report.c:202
 kasan_report_error mm/kasan/report.c:291
 kasan_report+0x252/0x510 mm/kasan/report.c:347
 check_memory_region_inline mm/kasan/kasan.c:326
 check_memory_region+0x139/0x190 mm/kasan/kasan.c:333
 memcpy+0x23/0x50 mm/kasan/kasan.c:368
 pfkey_sadb2xfrm_user_sec_ctx net/key/af_key.c:474
 pfkey_compile_policy+0x8e6/0xd40 net/key/af_key.c:3294
 xfrm_user_policy+0x349/0x560 net/xfrm/xfrm_state.c:1892
 do_ip_setsockopt.isra.12+0x1d05/0x38c0 net/ipv4/ip_sockglue.c:1175
 ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
 tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2732
 sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2750
 SYSC_setsockopt net/socket.c:1798
 SyS_setsockopt+0x270/0x3a0 net/socket.c:1777
 entry_SYSCALL_64_fastpath+0x1f/0xbe arch/x86/entry/entry_64.S:204
RIP: 0033:0x7f13a0968b79
RSP: 002b:00007fff131bc3f8 EFLAGS: 00000206 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007fff131bc550 RCX: 00007f13a0968b79
RDX: 0000000000000010 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000004004e0 R08: 00000000000000c2 R09: 0000000000000000
R10: 0000000020a2ff3e R11: 0000000000000206 R12: 0000000000000000
R13: 00007fff131bc550 R14: 0000000000000000 R15: 0000000000000000
Object at ffff88006701f780, in cache kmalloc-256 size: 256
Allocated:
PID = 4181
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 __kmalloc+0xa0/0x2d0 mm/slub.c:3745
 kmalloc ./include/linux/slab.h:495
 xfrm_user_policy+0xd8/0x560 net/xfrm/xfrm_state.c:1881
 do_ip_setsockopt.isra.12+0x1d05/0x38c0 net/ipv4/ip_sockglue.c:1175
 ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
 tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2732
 sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2750
 SYSC_setsockopt net/socket.c:1798
 SyS_setsockopt+0x270/0x3a0 net/socket.c:1777
 entry_SYSCALL_64_fastpath+0x1f/0xbe arch/x86/entry/entry_64.S:204
Freed:
PID = 3951
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525
 kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:589
 slab_free_hook mm/slub.c:1357
 slab_free_freelist_hook mm/slub.c:1379
 slab_free mm/slub.c:2961
 kfree+0xe8/0x2b0 mm/slub.c:3882
 free_bprm+0x19d/0x200 fs/exec.c:1382
 do_execveat_common.isra.34+0x19ad/0x2220 fs/exec.c:1778
 do_execve fs/exec.c:1813
 SYSC_execve fs/exec.c:1894
 SyS_execve+0x39/0x50 fs/exec.c:1889
 do_syscall_64+0x2c7/0x7a0 arch/x86/entry/common.c:281
 return_from_SYSCALL_64+0x0/0x7a arch/x86/entry/entry_64.S:246
Memory state around the buggy address:
 ffff88006701f700: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88006701f780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88006701f800: 00 00 00 00 00 00 00 00 02 fc fc fc fc fc fc fc
                                           ^
 ffff88006701f880: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff88006701f900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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