KASAN: slab-out-of-bounds Read in fl6_update_dst

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    2ef96a5b Linux 5.7-rc5
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=155f1714100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=efdde85c3af536b5
dashboard link: https://syzkaller.appspot.com/bug?extid=e8c028b62439eac42073
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=102bfda2100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13f8510c100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e8c028b62439eac42073@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: slab-out-of-bounds in fl6_update_dst+0x2bb/0x2c0 net/ipv6/exthdrs.c:1356
Read of size 16 at addr ffff88809dc23258 by task syz-executor528/7035

CPU: 1 PID: 7035 Comm: syz-executor528 Not tainted 5.7.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:382
 __kasan_report.cold+0x35/0x4d mm/kasan/report.c:511
 kasan_report+0x33/0x50 mm/kasan/common.c:625
 fl6_update_dst+0x2bb/0x2c0 net/ipv6/exthdrs.c:1356
 sctp_v6_get_dst+0x5e7/0x1c30 net/sctp/ipv6.c:276
 sctp_transport_route+0x125/0x350 net/sctp/transport.c:297
 sctp_assoc_add_peer+0x5a0/0x1030 net/sctp/associola.c:659
 sctp_connect_new_asoc+0x19b/0x580 net/sctp/socket.c:1092
 sctp_sendmsg_new_asoc net/sctp/socket.c:1694 [inline]
 sctp_sendmsg+0x1396/0x1f30 net/sctp/socket.c:2004
 inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:807
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x308/0x7e0 net/socket.c:2362
 ___sys_sendmsg+0x100/0x170 net/socket.c:2416
 __sys_sendmmsg+0x195/0x480 net/socket.c:2506
 __do_sys_sendmmsg net/socket.c:2535 [inline]
 __se_sys_sendmmsg net/socket.c:2532 [inline]
 __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2532
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x440309
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff01fee1f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440309
RDX: 0000000000000001 RSI: 0000000020000140 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401b90
R13: 0000000000401c20 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 7035:
 save_stack+0x1b/0x40 mm/kasan/common.c:49
 set_track mm/kasan/common.c:57 [inline]
 __kasan_kmalloc mm/kasan/common.c:495 [inline]
 __kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:468
 __do_kmalloc mm/slab.c:3656 [inline]
 __kmalloc+0x161/0x7a0 mm/slab.c:3665
 kmalloc include/linux/slab.h:560 [inline]
 sock_kmalloc net/core/sock.c:2166 [inline]
 sock_kmalloc+0xb5/0x100 net/core/sock.c:2157
 ipv6_renew_options+0x274/0x940 net/ipv6/exthdrs.c:1275
 do_ipv6_setsockopt.isra.0+0x2eaf/0x42f0 net/ipv6/ipv6_sockglue.c:435
 ipv6_setsockopt+0xfb/0x180 net/ipv6/ipv6_sockglue.c:949
 sctp_setsockopt+0x13e/0x7090 net/sctp/socket.c:4685
 __sys_setsockopt+0x248/0x480 net/socket.c:2132
 __do_sys_setsockopt net/socket.c:2148 [inline]
 __se_sys_setsockopt net/socket.c:2145 [inline]
 __x64_sys_setsockopt+0xba/0x150 net/socket.c:2145
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3

Freed by task 5138:
 save_stack+0x1b/0x40 mm/kasan/common.c:49
 set_track mm/kasan/common.c:57 [inline]
 kasan_set_free_info mm/kasan/common.c:317 [inline]
 __kasan_slab_free+0xf7/0x140 mm/kasan/common.c:456
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x109/0x2b0 mm/slab.c:3757
 tomoyo_path_perm+0x236/0x400 security/tomoyo/file.c:842
 security_inode_getattr+0xeb/0x150 security/security.c:1273
 vfs_getattr+0x22/0x60 fs/stat.c:117
 vfs_statx_fd+0x6a/0xb0 fs/stat.c:147
 vfs_fstat include/linux/fs.h:3295 [inline]
 __do_sys_newfstat+0x8b/0x100 fs/stat.c:388
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3

The buggy address belongs to the object at ffff88809dc23200
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 88 bytes inside of
 96-byte region [ffff88809dc23200, ffff88809dc23260)
The buggy address belongs to the page:
page:ffffea00027708c0 refcount:1 mapcount:0 mapping:0000000031b2e39e index:0xffff88809dc23080
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00027c7888 ffffea00027fc588 ffff8880aa000540
raw: ffff88809dc23080 ffff88809dc23000 000000010000001e 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809dc23100: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
 ffff88809dc23180: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
>ffff88809dc23200: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc
                                                    ^
 ffff88809dc23280: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff88809dc23300: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
==================================================================


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