[PATCH net] bpf, sockmap: fix race in sock_map_free()

[PATCH net] bpf, sockmap: fix race in sock_map_free()

[Eric Dumazet]

sock_map_free() calls release_sock(sk) without owning a reference
on the socket. This can cause use-after-free as syzbot found [1]

Jakub Sitnicki already took care of a similar issue
in sock_hash_free() in commit 75e68e5bf2c7 ("bpf, sockhash:
Synchronize delete from bucket list on map free")

[1]
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 0 PID: 3785 at lib/refcount.c:31 refcount_warn_saturate+0x17c/0x1a0 lib/refcount.c:31
Modules linked in:
CPU: 0 PID: 3785 Comm: kworker/u4:6 Not tainted 6.1.0-rc7-syzkaller-00103-gef4d3ea40565 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Workqueue: events_unbound bpf_map_free_deferred
RIP: 0010:refcount_warn_saturate+0x17c/0x1a0 lib/refcount.c:31
Code: 68 8b 31 c0 e8 75 71 15 fd 0f 0b e9 64 ff ff ff e8 d9 6e 4e fd c6 05 62 9c 3d 0a 01 48 c7 c7 80 bb 68 8b 31 c0 e8 54 71 15 fd <0f> 0b e9 43 ff ff ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c a2 fe ff
RSP: 0018:ffffc9000456fb60 EFLAGS: 00010246
RAX: eae59bab72dcd700 RBX: 0000000000000004 RCX: ffff8880207057c0
RDX: 0000000000000000 RSI: 0000000000000201 RDI: 0000000000000000
RBP: 0000000000000004 R08: ffffffff816fdabd R09: fffff520008adee5
R10: fffff520008adee5 R11: 1ffff920008adee4 R12: 0000000000000004
R13: dffffc0000000000 R14: ffff88807b1c6c00 R15: 1ffff1100f638dcf
FS: 0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b30c30000 CR3: 000000000d08e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__refcount_dec include/linux/refcount.h:344 [inline]
refcount_dec include/linux/refcount.h:359 [inline]
__sock_put include/net/sock.h:779 [inline]
tcp_release_cb+0x2d0/0x360 net/ipv4/tcp_output.c:1092
release_sock+0xaf/0x1c0 net/core/sock.c:3468
sock_map_free+0x219/0x2c0 net/core/sock_map.c:356
process_one_work+0x81c/0xd10 kernel/workqueue.c:2289
worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
kthread+0x266/0x300 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
</TASK>

Fixes: 7e81a3530206 ("bpf: Sockmap, ensure sock lock held during tear down")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Jakub Sitnicki <jakub@cloudflare.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Song Liu <songliubraving@fb.com>
---
 net/core/sock_map.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 81beb16ab1ebfcb166f51f89a029fe1c28a629a4..22fa2c5bc6ec9652c4e4a904990a5b7635c20cb6 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -349,11 +349,13 @@ static void sock_map_free(struct bpf_map *map)
 
 		sk = xchg(psk, NULL);
 		if (sk) {
+			sock_hold(sk);
 			lock_sock(sk);
 			rcu_read_lock();
 			sock_map_unref(sk, psk);
 			rcu_read_unlock();
 			release_sock(sk);
+			sock_put(sk);
 		}
 	}
 
-- 
2.39.0.rc0.267.gcb52ba06e7-goog

RE: [PATCH net] bpf, sockmap: fix race in sock_map_free()

[John Fastabend]

Eric Dumazet wrote:
> sock_map_free() calls release_sock(sk) without owning a reference
> on the socket. This can cause use-after-free as syzbot found [1]
> 
> Jakub Sitnicki already took care of a similar issue
> in sock_hash_free() in commit 75e68e5bf2c7 ("bpf, sockhash:
> Synchronize delete from bucket list on map free")
> 
> [1]
> refcount_t: decrement hit 0; leaking memory.
> WARNING: CPU: 0 PID: 3785 at lib/refcount.c:31 refcount_warn_saturate+0x17c/0x1a0 lib/refcount.c:31
> Modules linked in:
> CPU: 0 PID: 3785 Comm: kworker/u4:6 Not tainted 6.1.0-rc7-syzkaller-00103-gef4d3ea40565 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> Workqueue: events_unbound bpf_map_free_deferred
> RIP: 0010:refcount_warn_saturate+0x17c/0x1a0 lib/refcount.c:31
> Code: 68 8b 31 c0 e8 75 71 15 fd 0f 0b e9 64 ff ff ff e8 d9 6e 4e fd c6 05 62 9c 3d 0a 01 48 c7 c7 80 bb 68 8b 31 c0 e8 54 71 15 fd <0f> 0b e9 43 ff ff ff 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c a2 fe ff
> RSP: 0018:ffffc9000456fb60 EFLAGS: 00010246
> RAX: eae59bab72dcd700 RBX: 0000000000000004 RCX: ffff8880207057c0
> RDX: 0000000000000000 RSI: 0000000000000201 RDI: 0000000000000000
> RBP: 0000000000000004 R08: ffffffff816fdabd R09: fffff520008adee5
> R10: fffff520008adee5 R11: 1ffff920008adee4 R12: 0000000000000004
> R13: dffffc0000000000 R14: ffff88807b1c6c00 R15: 1ffff1100f638dcf
> FS: 0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b30c30000 CR3: 000000000d08e000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> __refcount_dec include/linux/refcount.h:344 [inline]
> refcount_dec include/linux/refcount.h:359 [inline]
> __sock_put include/net/sock.h:779 [inline]
> tcp_release_cb+0x2d0/0x360 net/ipv4/tcp_output.c:1092
> release_sock+0xaf/0x1c0 net/core/sock.c:3468
> sock_map_free+0x219/0x2c0 net/core/sock_map.c:356
> process_one_work+0x81c/0xd10 kernel/workqueue.c:2289
> worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
> kthread+0x266/0x300 kernel/kthread.c:376
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
> </TASK>
> 
> Fixes: 7e81a3530206 ("bpf: Sockmap, ensure sock lock held during tear down")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Cc: Jakub Sitnicki <jakub@cloudflare.com>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Song Liu <songliubraving@fb.com>

Thanks.

Acked-by: John Fastabend <john.fastabend@gmail.com>

Re: [PATCH net] bpf, sockmap: fix race in sock_map_free()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Fri,  2 Dec 2022 11:16:40 +0000 you wrote:
> sock_map_free() calls release_sock(sk) without owning a reference
> on the socket. This can cause use-after-free as syzbot found [1]
> 
> Jakub Sitnicki already took care of a similar issue
> in sock_hash_free() in commit 75e68e5bf2c7 ("bpf, sockhash:
> Synchronize delete from bucket list on map free")
> 
> [...]

Here is the summary with links:
  - [net] bpf, sockmap: fix race in sock_map_free()
    https://git.kernel.org/bpf/bpf-next/c/0a182f8d6074

You are awesome, thank you!
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