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

[John Fastabend <john.fastabend@gmail.com>]

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>