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Date: Mon, 13 Nov 2023 10:34:33 -0800
From: Rao Shoaib <rao.shoaib@...cle.com>
To: Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller"
 <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzbot+7a2d546fa43e49315ed3@...kaller.appspotmail.com
Subject: Re: [PATCH net] af_unix: fix use-after-free in
 unix_stream_read_actor()

Looks good!

Reviewed-by: Rao shoaib <rao.shoaib@...cle.com>

On 11/13/23 05:49, Eric Dumazet wrote:
> syzbot reported the following crash [1]
> 
> After releasing unix socket lock, u->oob_skb can be changed
> by another thread. We must temporarily increase skb refcount
> to make sure this other thread will not free the skb under us.
> 
> [1]
> 
> BUG: KASAN: slab-use-after-free in unix_stream_read_actor+0xa7/0xc0 net/unix/af_unix.c:2866
> Read of size 4 at addr ffff88801f3b9cc4 by task syz-executor107/5297
> 
> CPU: 1 PID: 5297 Comm: syz-executor107 Not tainted 6.6.0-syzkaller-15910-gb8e3a87a627b #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
> print_address_description mm/kasan/report.c:364 [inline]
> print_report+0xc4/0x620 mm/kasan/report.c:475
> kasan_report+0xda/0x110 mm/kasan/report.c:588
> unix_stream_read_actor+0xa7/0xc0 net/unix/af_unix.c:2866
> unix_stream_recv_urg net/unix/af_unix.c:2587 [inline]
> unix_stream_read_generic+0x19a5/0x2480 net/unix/af_unix.c:2666
> unix_stream_recvmsg+0x189/0x1b0 net/unix/af_unix.c:2903
> sock_recvmsg_nosec net/socket.c:1044 [inline]
> sock_recvmsg+0xe2/0x170 net/socket.c:1066
> ____sys_recvmsg+0x21f/0x5c0 net/socket.c:2803
> ___sys_recvmsg+0x115/0x1a0 net/socket.c:2845
> __sys_recvmsg+0x114/0x1e0 net/socket.c:2875
> do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:82
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
> RIP: 0033:0x7fc67492c559
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fc6748ab228 EFLAGS: 00000246 ORIG_RAX: 000000000000002f
> RAX: ffffffffffffffda RBX: 000000000000001c RCX: 00007fc67492c559
> RDX: 0000000040010083 RSI: 0000000020000140 RDI: 0000000000000004
> RBP: 00007fc6749b6348 R08: 00007fc6748ab6c0 R09: 00007fc6748ab6c0
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc6749b6340
> R13: 00007fc6749b634c R14: 00007ffe9fac52a0 R15: 00007ffe9fac5388
> </TASK>
> 
> Allocated by task 5295:
> kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
> kasan_set_track+0x25/0x30 mm/kasan/common.c:52
> __kasan_slab_alloc+0x81/0x90 mm/kasan/common.c:328
> kasan_slab_alloc include/linux/kasan.h:188 [inline]
> slab_post_alloc_hook mm/slab.h:763 [inline]
> slab_alloc_node mm/slub.c:3478 [inline]
> kmem_cache_alloc_node+0x180/0x3c0 mm/slub.c:3523
> __alloc_skb+0x287/0x330 net/core/skbuff.c:641
> alloc_skb include/linux/skbuff.h:1286 [inline]
> alloc_skb_with_frags+0xe4/0x710 net/core/skbuff.c:6331
> sock_alloc_send_pskb+0x7e4/0x970 net/core/sock.c:2780
> sock_alloc_send_skb include/net/sock.h:1884 [inline]
> queue_oob net/unix/af_unix.c:2147 [inline]
> unix_stream_sendmsg+0xb5f/0x10a0 net/unix/af_unix.c:2301
> sock_sendmsg_nosec net/socket.c:730 [inline]
> __sock_sendmsg+0xd5/0x180 net/socket.c:745
> ____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
> ___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
> __sys_sendmsg+0x117/0x1e0 net/socket.c:2667
> do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:82
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> Freed by task 5295:
> kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
> kasan_set_track+0x25/0x30 mm/kasan/common.c:52
> kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
> ____kasan_slab_free mm/kasan/common.c:236 [inline]
> ____kasan_slab_free+0x15b/0x1b0 mm/kasan/common.c:200
> kasan_slab_free include/linux/kasan.h:164 [inline]
> slab_free_hook mm/slub.c:1800 [inline]
> slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
> slab_free mm/slub.c:3809 [inline]
> kmem_cache_free+0xf8/0x340 mm/slub.c:3831
> kfree_skbmem+0xef/0x1b0 net/core/skbuff.c:1015
> __kfree_skb net/core/skbuff.c:1073 [inline]
> consume_skb net/core/skbuff.c:1288 [inline]
> consume_skb+0xdf/0x170 net/core/skbuff.c:1282
> queue_oob net/unix/af_unix.c:2178 [inline]
> unix_stream_sendmsg+0xd49/0x10a0 net/unix/af_unix.c:2301
> sock_sendmsg_nosec net/socket.c:730 [inline]
> __sock_sendmsg+0xd5/0x180 net/socket.c:745
> ____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
> ___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
> __sys_sendmsg+0x117/0x1e0 net/socket.c:2667
> do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:82
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> The buggy address belongs to the object at ffff88801f3b9c80
> which belongs to the cache skbuff_head_cache of size 240
> The buggy address is located 68 bytes inside of
> freed 240-byte region [ffff88801f3b9c80, ffff88801f3b9d70)
> 
> The buggy address belongs to the physical page:
> page:ffffea00007cee40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1f3b9
> flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
> page_type: 0xffffffff()
> raw: 00fff00000000800 ffff888142a60640 dead000000000122 0000000000000000
> raw: 0000000000000000 00000000000c000c 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 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 5299, tgid 5283 (syz-executor107), ts 103803840339, free_ts 103600093431
> set_page_owner include/linux/page_owner.h:31 [inline]
> post_alloc_hook+0x2cf/0x340 mm/page_alloc.c:1537
> prep_new_page mm/page_alloc.c:1544 [inline]
> get_page_from_freelist+0xa25/0x36c0 mm/page_alloc.c:3312
> __alloc_pages+0x1d0/0x4a0 mm/page_alloc.c:4568
> alloc_pages_mpol+0x258/0x5f0 mm/mempolicy.c:2133
> alloc_slab_page mm/slub.c:1870 [inline]
> allocate_slab+0x251/0x380 mm/slub.c:2017
> new_slab mm/slub.c:2070 [inline]
> ___slab_alloc+0x8c7/0x1580 mm/slub.c:3223
> __slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3322
> __slab_alloc_node mm/slub.c:3375 [inline]
> slab_alloc_node mm/slub.c:3468 [inline]
> kmem_cache_alloc_node+0x132/0x3c0 mm/slub.c:3523
> __alloc_skb+0x287/0x330 net/core/skbuff.c:641
> alloc_skb include/linux/skbuff.h:1286 [inline]
> alloc_skb_with_frags+0xe4/0x710 net/core/skbuff.c:6331
> sock_alloc_send_pskb+0x7e4/0x970 net/core/sock.c:2780
> sock_alloc_send_skb include/net/sock.h:1884 [inline]
> queue_oob net/unix/af_unix.c:2147 [inline]
> unix_stream_sendmsg+0xb5f/0x10a0 net/unix/af_unix.c:2301
> sock_sendmsg_nosec net/socket.c:730 [inline]
> __sock_sendmsg+0xd5/0x180 net/socket.c:745
> ____sys_sendmsg+0x6ac/0x940 net/socket.c:2584
> ___sys_sendmsg+0x135/0x1d0 net/socket.c:2638
> __sys_sendmsg+0x117/0x1e0 net/socket.c:2667
> page last free stack trace:
> reset_page_owner include/linux/page_owner.h:24 [inline]
> free_pages_prepare mm/page_alloc.c:1137 [inline]
> free_unref_page_prepare+0x4f8/0xa90 mm/page_alloc.c:2347
> free_unref_page+0x33/0x3b0 mm/page_alloc.c:2487
> __unfreeze_partials+0x21d/0x240 mm/slub.c:2655
> qlink_free mm/kasan/quarantine.c:168 [inline]
> qlist_free_all+0x6a/0x170 mm/kasan/quarantine.c:187
> kasan_quarantine_reduce+0x18e/0x1d0 mm/kasan/quarantine.c:294
> __kasan_slab_alloc+0x65/0x90 mm/kasan/common.c:305
> kasan_slab_alloc include/linux/kasan.h:188 [inline]
> slab_post_alloc_hook mm/slab.h:763 [inline]
> slab_alloc_node mm/slub.c:3478 [inline]
> slab_alloc mm/slub.c:3486 [inline]
> __kmem_cache_alloc_lru mm/slub.c:3493 [inline]
> kmem_cache_alloc+0x15d/0x380 mm/slub.c:3502
> vm_area_dup+0x21/0x2f0 kernel/fork.c:500
> __split_vma+0x17d/0x1070 mm/mmap.c:2365
> split_vma mm/mmap.c:2437 [inline]
> vma_modify+0x25d/0x450 mm/mmap.c:2472
> vma_modify_flags include/linux/mm.h:3271 [inline]
> mprotect_fixup+0x228/0xc80 mm/mprotect.c:635
> do_mprotect_pkey+0x852/0xd60 mm/mprotect.c:809
> __do_sys_mprotect mm/mprotect.c:830 [inline]
> __se_sys_mprotect mm/mprotect.c:827 [inline]
> __x64_sys_mprotect+0x78/0xb0 mm/mprotect.c:827
> do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> do_syscall_64+0x3f/0x110 arch/x86/entry/common.c:82
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> Memory state around the buggy address:
> ffff88801f3b9b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88801f3b9c00: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
>> ffff88801f3b9c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff88801f3b9d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
> ffff88801f3b9d80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
> 
> Fixes: 876c14ad014d ("af_unix: fix holding spinlock in oob handling")
> Reported-and-tested-by: syzbot+7a2d546fa43e49315ed3@...kaller.appspotmail.com
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Rao Shoaib <rao.shoaib@...cle.com>
> ---
>   net/unix/af_unix.c | 9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 45506a95b25f8acdb99699c3c9256f50d0e7e5d0..a357dc5f24046d98674da9935eccbb9e18ea4616 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2581,15 +2581,16 @@ static int unix_stream_recv_urg(struct unix_stream_read_state *state)
>   
>   	if (!(state->flags & MSG_PEEK))
>   		WRITE_ONCE(u->oob_skb, NULL);
> -
> +	else
> +		skb_get(oob_skb);
>   	unix_state_unlock(sk);
>   
>   	chunk = state->recv_actor(oob_skb, 0, chunk, state);
>   
> -	if (!(state->flags & MSG_PEEK)) {
> +	if (!(state->flags & MSG_PEEK))
>   		UNIXCB(oob_skb).consumed += 1;
> -		kfree_skb(oob_skb);
> -	}
> +
> +	consume_skb(oob_skb);
>   
>   	mutex_unlock(&u->iolock);
>   

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