From b9bb53f3836f4eb2bdeb3447be11042bd29c2408 Mon Sep 17 00:00:00 2001 From: Willem de Bruijn Date: Tue, 5 Apr 2016 12:41:14 -0400 Subject: [PATCH] sock: convert sk_peek_offset functions to WRITE_ONCE Make the peek offset interface safe to use in lockless environments. Use READ_ONCE and WRITE_ONCE to avoid race conditions between testing and updating the peek offset. Suggested-by: Eric Dumazet Signed-off-by: Willem de Bruijn Signed-off-by: David S. Miller --- include/net/sock.h | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 310c4367ea83..09aec75eb184 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -459,26 +459,28 @@ struct sock { static inline int sk_peek_offset(struct sock *sk, int flags) { - if ((flags & MSG_PEEK) && (sk->sk_peek_off >= 0)) - return sk->sk_peek_off; - else - return 0; + if (unlikely(flags & MSG_PEEK)) { + s32 off = READ_ONCE(sk->sk_peek_off); + if (off >= 0) + return off; + } + + return 0; } static inline void sk_peek_offset_bwd(struct sock *sk, int val) { - if (sk->sk_peek_off >= 0) { - if (sk->sk_peek_off >= val) - sk->sk_peek_off -= val; - else - sk->sk_peek_off = 0; + s32 off = READ_ONCE(sk->sk_peek_off); + + if (unlikely(off >= 0)) { + off = max_t(s32, off - val, 0); + WRITE_ONCE(sk->sk_peek_off, off); } } static inline void sk_peek_offset_fwd(struct sock *sk, int val) { - if (sk->sk_peek_off >= 0) - sk->sk_peek_off += val; + sk_peek_offset_bwd(sk, -val); } /* -- 2.20.1