netdev - [bpf PATCH] bpf: sockmap missing NULL psock check

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180103034705.11636.98766.stgit@john-Precision-Tower-5810>
Date:   Tue, 02 Jan 2018 19:47:05 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     borkmann@...earbox.net, alexei.starovoitov@...il.com
Cc:     netdev@...r.kernel.org
Subject: [bpf PATCH] bpf: sockmap missing NULL psock check

Add psock NULL check to handle a racing sock event that can get the
sk_callback_lock before this case but after xchg happens causing the
refcnt to hit zero and sock user data (psock) to be null and queued
for garbage collection.

Also add a comment in the code because this is a bit subtle and
not obvious in my opinion.

Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 kernel/bpf/sockmap.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 5ee2e41..dfbbde2 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -591,6 +591,13 @@ static void sock_map_free(struct bpf_map *map)
 
 		write_lock_bh(&sock->sk_callback_lock);
 		psock = smap_psock_sk(sock);
+		/* This check handles a racing sock event that can get the
+		 * sk_callback_lock before this case but after xchg happens
+		 * causing the refcnt to hit zero and sock user data (psock)
+		 * to be null and queued for garbage collection.
+		 */
+		if (unlikely(!psock))
+			continue;
 		smap_list_remove(psock, &stab->sock_map[i]);
 		smap_release_sock(psock, sock);
 		write_unlock_bh(&sock->sk_callback_lock);