Re: [syzbot] KASAN: use-after-free Write in null_skcipher_crypt

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On 8/17/21 8:24 PM, syzbot wrote:

Hello,

syzbot found the following issue on:

HEAD commit:    a9a507013a6f Merge tag 'ieee802154-for-davem-2021-08-12' o..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=16647ca1300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=343fd21f6f4da2d6
dashboard link: https://syzkaller.appspot.com/bug?extid=d2c5e6980bfc84513464
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14989fe9300000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12b1a779300000

The issue was bisected to:

commit 8d2cb3ad31181f050af4d46d6854cf332d1207a9
Author: Calvin Johnson <calvin.johnson@xxxxxxxxxxx>
Date:   Fri Jun 11 10:53:55 2021 +0000

     of: mdio: Refactor of_mdiobus_register_phy()

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=106b97d6300000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=126b97d6300000
console output: https://syzkaller.appspot.com/x/log.txt?x=146b97d6300000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d2c5e6980bfc84513464@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 8d2cb3ad3118 ("of: mdio: Refactor of_mdiobus_register_phy()")

==================================================================
BUG: KASAN: use-after-free in memcpy include/linux/fortify-string.h:191 [inline]
BUG: KASAN: use-after-free in null_skcipher_crypt+0xa8/0x120 crypto/crypto_null.c:85
Write of size 4096 at addr ffff88801c040000 by task syz-executor554/8455

CPU: 0 PID: 8455 Comm: syz-executor554 Not tainted 5.14.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:88 [inline]
  dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:105
  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
  memcpy+0x39/0x60 mm/kasan/shadow.c:66
  memcpy include/linux/fortify-string.h:191 [inline]
  null_skcipher_crypt+0xa8/0x120 crypto/crypto_null.c:85
  crypto_skcipher_encrypt+0xaa/0xf0 crypto/skcipher.c:630
  crypto_authenc_encrypt+0x3b4/0x510 crypto/authenc.c:222
  crypto_aead_encrypt+0xaa/0xf0 crypto/aead.c:94
  esp6_output_tail+0x777/0x1a90 net/ipv6/esp6.c:659
  esp6_output+0x4af/0x8a0 net/ipv6/esp6.c:735
  xfrm_output_one net/xfrm/xfrm_output.c:552 [inline]
  xfrm_output_resume+0x2997/0x5ae0 net/xfrm/xfrm_output.c:587
  xfrm_output2 net/xfrm/xfrm_output.c:614 [inline]
  xfrm_output+0x2e7/0xff0 net/xfrm/xfrm_output.c:744
  __xfrm6_output+0x4c3/0x1260 net/ipv6/xfrm6_output.c:87
  NF_HOOK_COND include/linux/netfilter.h:296 [inline]
  xfrm6_output+0x117/0x550 net/ipv6/xfrm6_output.c:92
  dst_output include/net/dst.h:448 [inline]
  ip6_local_out+0xaf/0x1a0 net/ipv6/output_core.c:161
  ip6_send_skb+0xb7/0x340 net/ipv6/ip6_output.c:1935
  ip6_push_pending_frames+0xdd/0x100 net/ipv6/ip6_output.c:1955
  rawv6_push_pending_frames net/ipv6/raw.c:613 [inline]
  rawv6_sendmsg+0x2a87/0x3990 net/ipv6/raw.c:956
  inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:821
  sock_sendmsg_nosec net/socket.c:703 [inline]
  sock_sendmsg+0xcf/0x120 net/socket.c:723
  ____sys_sendmsg+0x6e8/0x810 net/socket.c:2392
  ___sys_sendmsg+0xf3/0x170 net/socket.c:2446
  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2475
  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: 0033:0x43f4b9
Code: 1d 01 00 85 c0 b8 00 00 00 00 48 0f 44 c3 5b c3 90 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc1e9cfff8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043f4b9
RDX: 0000000000000000 RSI: 0000000020000500 RDI: 0000000000000004
RBP: 0000000000000005 R08: 6c616b7a79732f2e R09: 6c616b7a79732f2e
R10: 00000000000000e8 R11: 0000000000000246 R12: 00000000004034b0
R13: 0000000000000000 R14: 00000000004ad018 R15: 0000000000400488

Allocated by task 1:
  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_slab_alloc+0x84/0xa0 mm/kasan/common.c:467
  kasan_slab_alloc include/linux/kasan.h:254 [inline]
  slab_post_alloc_hook mm/slab.h:519 [inline]
  slab_alloc_node mm/slub.c:2956 [inline]
  slab_alloc mm/slub.c:2964 [inline]
  kmem_cache_alloc+0x285/0x4a0 mm/slub.c:2969
  getname_flags.part.0+0x50/0x4f0 fs/namei.c:138
  getname_flags fs/namei.c:2747 [inline]
  user_path_at_empty+0xa1/0x100 fs/namei.c:2747
  user_path_at include/linux/namei.h:57 [inline]
  vfs_statx+0x142/0x390 fs/stat.c:203
  vfs_fstatat fs/stat.c:225 [inline]
  vfs_lstat include/linux/fs.h:3386 [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

Freed by task 1:
  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:230 [inline]
  slab_free_hook mm/slub.c:1625 [inline]
  slab_free_freelist_hook+0xdf/0x240 mm/slub.c:1650
  slab_free mm/slub.c:3210 [inline]
  kmem_cache_free+0x8a/0x5b0 mm/slub.c:3226
  putname+0xe1/0x120 fs/namei.c:259


(*)


  filename_lookup+0x3df/0x5b0 fs/namei.c:2477
  user_path_at include/linux/namei.h:57 [inline]
  vfs_statx+0x142/0x390 fs/stat.c:203
  vfs_fstatat fs/stat.c:225 [inline]
  vfs_lstat include/linux/fs.h:3386 [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



+CC Dmitry
I think, it was caused by 9d96ea38873f ("namei: change filename_parentat() calling conventions"). 

Now what looks strange to me

Upstream version:

static struct filename *filename_parentat(...)
{
...
	retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
...
	if (likely(!retval)) {
		*last = nd.last;
		*type = nd.last_type;
		audit_inode(name, parent->dentry, AUDIT_INODE_PARENT);
	} else {
		putname(name);  <-- putting name if retval if not-zero
		name = ERR_PTR(retval);
	}

}


Linux-next version:

static int __filename_parentat(...)
{

	retval = path_parentat(&nd, flags | LOOKUP_RCU, parent);
...
	if (likely(!retval)) {
		*last = nd.last;
		*type = nd.last_type;
		audit_inode(name, parent->dentry, AUDIT_INODE_PARENT);
	}
	restore_nameidata();
	return retval;
}

static int filename_parentat(...)
{
	int retval = __filename_parentat(...);

	putname(name);   <-- always putting the name
	return retval;
}

And bug report says, that name was freed by this put (*)

I guess, we should do smth like:

if (retval)
	putname(name);
I didn't dig into details, because Dmitry's patch series was really huge, so it's just for thoughts ;) 




With regards,
Pavel Skripkin
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