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

[Pavel Skripkin <paskripkin@xxxxxxxxx>]

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