Date:   Fri, 16 Jul 2021 16:01:01 -0400
From:   Xin Long <lucien.xin@...il.com>
To:     syzbot <syzbot+b774577370208727d12b@...kaller.appspotmail.com>
Cc:     davem <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-sctp @ vger . kernel . org" <linux-sctp@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        network dev <netdev@...r.kernel.org>,
        Neil Horman <nhorman@...driver.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vlad Yasevich <vyasevich@...il.com>
Subject: Re: [syzbot] KASAN: use-after-free Write in sctp_auth_shkey_hold

On Mon, Jul 12, 2021 at 12:46 AM syzbot
<syzbot+b774577370208727d12b@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    5e437416 Merge branch 'dsa-mv88e6xxx-topaz-fixes'
> git tree:       net-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14503bac300000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4cb84363d46e9fc3
> dashboard link: https://syzkaller.appspot.com/bug?extid=b774577370208727d12b
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b774577370208727d12b@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
> BUG: KASAN: use-after-free in atomic_fetch_add_relaxed include/asm-generic/atomic-instrumented.h:111 [inline]
> BUG: KASAN: use-after-free in __refcount_add include/linux/refcount.h:193 [inline]
> BUG: KASAN: use-after-free in __refcount_inc include/linux/refcount.h:250 [inline]
> BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
> BUG: KASAN: use-after-free in sctp_auth_shkey_hold+0x22/0xa0 net/sctp/auth.c:112
> Write of size 4 at addr ffff88802053ad58 by task syz-executor.1/31590
>
> CPU: 0 PID: 31590 Comm: syz-executor.1 Not tainted 5.13.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:96
>  print_address_description.constprop.0.cold+0x6c/0x309 mm/kasan/report.c:233
>  __kasan_report mm/kasan/report.c:419 [inline]
>  kasan_report.cold+0x83/0xdf mm/kasan/report.c:436
>  check_region_inline mm/kasan/generic.c:183 [inline]
>  kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
>  instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
>  atomic_fetch_add_relaxed include/asm-generic/atomic-instrumented.h:111 [inline]
>  __refcount_add include/linux/refcount.h:193 [inline]
>  __refcount_inc include/linux/refcount.h:250 [inline]
>  refcount_inc include/linux/refcount.h:267 [inline]
>  sctp_auth_shkey_hold+0x22/0xa0 net/sctp/auth.c:112
>  sctp_set_owner_w net/sctp/socket.c:131 [inline]
>  sctp_sendmsg_to_asoc+0x152e/0x2180 net/sctp/socket.c:1865
>  sctp_sendmsg+0x103b/0x1d30 net/sctp/socket.c:2027
>  inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:821
>  sock_sendmsg_nosec net/socket.c:702 [inline]
>  sock_sendmsg+0xcf/0x120 net/socket.c:722
>  ____sys_sendmsg+0x331/0x810 net/socket.c:2385
>  ___sys_sendmsg+0xf3/0x170 net/socket.c:2439
>  __sys_sendmmsg+0x195/0x470 net/socket.c:2525
>  __do_sys_sendmmsg net/socket.c:2554 [inline]
>  __se_sys_sendmmsg net/socket.c:2551 [inline]
>  __x64_sys_sendmmsg+0x99/0x100 net/socket.c:2551
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x4665d9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f679ad9b188 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
> RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9
> RDX: 0000000000000002 RSI: 0000000020002340 RDI: 0000000000000003
> RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf80
> R13: 00007ffc95431f0f R14: 00007f679ad9b300 R15: 0000000000022000
>
> Allocated by task 31590:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track mm/kasan/common.c:46 [inline]
>  set_alloc_info mm/kasan/common.c:434 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:513 [inline]
>  ____kasan_kmalloc mm/kasan/common.c:472 [inline]
>  __kasan_kmalloc+0x9b/0xd0 mm/kasan/common.c:522
>  kmalloc include/linux/slab.h:591 [inline]
>  kzalloc include/linux/slab.h:721 [inline]
>  sctp_auth_shkey_create+0x85/0x1f0 net/sctp/auth.c:84
>  sctp_auth_asoc_copy_shkeys+0x1e8/0x350 net/sctp/auth.c:363
>  sctp_association_init net/sctp/associola.c:257 [inline]
>  sctp_association_new+0x1829/0x2250 net/sctp/associola.c:298
>  sctp_connect_new_asoc+0x1ac/0x770 net/sctp/socket.c:1088
>  __sctp_connect+0x3d0/0xc30 net/sctp/socket.c:1194
>  sctp_connect net/sctp/socket.c:4804 [inline]
>  sctp_inet_connect+0x15e/0x200 net/sctp/socket.c:4819
>  __sys_connect_file+0x155/0x1a0 net/socket.c:1872
>  __sys_connect+0x161/0x190 net/socket.c:1889
>  __do_sys_connect net/socket.c:1899 [inline]
>  __se_sys_connect net/socket.c:1896 [inline]
>  __x64_sys_connect+0x6f/0xb0 net/socket.c:1896
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Freed by task 31590:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:38
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:46
>  kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:360
>  ____kasan_slab_free mm/kasan/common.c:366 [inline]
>  ____kasan_slab_free mm/kasan/common.c:328 [inline]
>  __kasan_slab_free+0xfb/0x130 mm/kasan/common.c:374
>  kasan_slab_free include/linux/kasan.h:229 [inline]
>  slab_free_hook mm/slub.c:1639 [inline]
>  slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1664
>  slab_free mm/slub.c:3224 [inline]
>  kfree+0xeb/0x670 mm/slub.c:4268
>  sctp_auth_shkey_destroy net/sctp/auth.c:101 [inline]
>  sctp_auth_shkey_release+0x100/0x160 net/sctp/auth.c:107
>  sctp_auth_set_key+0x508/0x6d0 net/sctp/auth.c:862
It seems caused by not updating asoc->shkey when the old key is being deleted:

diff --git a/net/sctp/auth.c b/net/sctp/auth.c
index 6f8319b..d095247 100644
--- a/net/sctp/auth.c
+++ b/net/sctp/auth.c
@@ -858,6 +858,8 @@ int sctp_auth_set_key(struct sctp_endpoint *ep,
        cur_key->key = key;

        if (replace) {
+               if (asoc && asoc->shkey == shkey)
+                       asoc->shkey = cur_key;
                list_del_init(&shkey->key_list);
                sctp_auth_shkey_release(shkey);
        }

>  sctp_setsockopt_auth_key net/sctp/socket.c:3643 [inline]
>  sctp_setsockopt+0x4919/0xa5e0 net/sctp/socket.c:4682
>  __sys_setsockopt+0x2db/0x610 net/socket.c:2152
>  __do_sys_setsockopt net/socket.c:2163 [inline]
>  __se_sys_setsockopt net/socket.c:2160 [inline]
>  __x64_sys_setsockopt+0xba/0x150 net/socket.c:2160
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The buggy address belongs to the object at ffff88802053ad40
>  which belongs to the cache kmalloc-32 of size 32
> The buggy address is located 24 bytes inside of
>  32-byte region [ffff88802053ad40, ffff88802053ad60)
> The buggy address belongs to the page:
> page:ffffea0000814e80 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2053a
> flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000200 dead000000000100 dead000000000122 ffff888010841500
> raw: 0000000000000000 0000000080400040 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY), pid 4873, ts 20137001110, free_ts 20080007470
>  prep_new_page mm/page_alloc.c:2445 [inline]
>  get_page_from_freelist+0xa72/0x2f80 mm/page_alloc.c:4178
>  __alloc_pages+0x1b2/0x500 mm/page_alloc.c:5386
>  alloc_pages+0x18c/0x2a0 mm/mempolicy.c:2272
>  alloc_slab_page mm/slub.c:1702 [inline]
>  allocate_slab+0x32b/0x4c0 mm/slub.c:1842
>  new_slab mm/slub.c:1905 [inline]
>  new_slab_objects mm/slub.c:2651 [inline]
>  ___slab_alloc+0x4ba/0x820 mm/slub.c:2814
>  __slab_alloc.constprop.0+0xa7/0xf0 mm/slub.c:2854
>  slab_alloc_node mm/slub.c:2936 [inline]
>  slab_alloc mm/slub.c:2978 [inline]
>  __kmalloc+0x312/0x330 mm/slub.c:4106
>  kmalloc include/linux/slab.h:596 [inline]
>  kzalloc include/linux/slab.h:721 [inline]
>  tomoyo_encode2.part.0+0xe9/0x3a0 security/tomoyo/realpath.c:45
>  tomoyo_encode2 security/tomoyo/realpath.c:31 [inline]
>  tomoyo_encode+0x28/0x50 security/tomoyo/realpath.c:80
>  tomoyo_realpath_from_path+0x186/0x620 security/tomoyo/realpath.c:288
>  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
>  tomoyo_path_perm+0x21b/0x400 security/tomoyo/file.c:822
>  security_inode_getattr+0xcf/0x140 security/security.c:1332
>  vfs_getattr fs/stat.c:139 [inline]
>  vfs_statx+0x164/0x390 fs/stat.c:207
>  vfs_fstatat fs/stat.c:225 [inline]
>  vfs_lstat include/linux/fs.h:3384 [inline]
>  __do_sys_newlstat+0x91/0x110 fs/stat.c:380
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
> page last free stack trace:
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1355 [inline]
>  free_pcp_prepare+0x2c5/0x780 mm/page_alloc.c:1406
>  free_unref_page_prepare mm/page_alloc.c:3341 [inline]
>  free_unref_page+0x19/0x690 mm/page_alloc.c:3420
>  qlink_free mm/kasan/quarantine.c:146 [inline]
>  qlist_free_all+0x5a/0xc0 mm/kasan/quarantine.c:165
>  kasan_quarantine_reduce+0x180/0x200 mm/kasan/quarantine.c:272
>  __kasan_slab_alloc+0x8e/0xa0 mm/kasan/common.c:444
>  kasan_slab_alloc include/linux/kasan.h:253 [inline]
>  slab_post_alloc_hook mm/slab.h:512 [inline]
>  slab_alloc_node mm/slub.c:2970 [inline]
>  slab_alloc mm/slub.c:2978 [inline]
>  kmem_cache_alloc+0x29b/0x4a0 mm/slub.c:2983
>  getname_flags.part.0+0x50/0x4f0 fs/namei.c:138
>  getname_flags include/linux/audit.h:319 [inline]
>  getname+0x8e/0xd0 fs/namei.c:209
>  do_sys_openat2+0xf5/0x420 fs/open.c:1189
>  do_sys_open fs/open.c:1211 [inline]
>  __do_sys_open fs/open.c:1219 [inline]
>  __se_sys_open fs/open.c:1215 [inline]
>  __x64_sys_open+0x119/0x1c0 fs/open.c:1215
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Memory state around the buggy address:
>  ffff88802053ac00: 00 00 00 02 fc fc fc fc fa fb fb fb fc fc fc fc
>  ffff88802053ac80: 00 00 00 00 fc fc fc fc fa fb fb fb fc fc fc fc
> >ffff88802053ad00: fb fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
>                                                     ^
>  ffff88802053ad80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>  ffff88802053ae00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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