3.16.82-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Guillaume Nault <gnault@xxxxxxxxxx> commit 721c8dafad26ccfa90ff659ee19755e3377b829d upstream. Syncookies borrow the ->rx_opt.ts_recent_stamp field to store the timestamp of the last synflood. Protect them with READ_ONCE() and WRITE_ONCE() since reads and writes aren't serialised. Use of .rx_opt.ts_recent_stamp for storing the synflood timestamp was introduced by a0f82f64e269 ("syncookies: remove last_synq_overflow from struct tcp_sock"). But unprotected accesses were already there when timestamp was stored in .last_synq_overflow. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Guillaume Nault <gnault@xxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> [bwh: Backported to 3.16: Use ACCESS_ONCE() instead of {READ,WRITE}_ONCE()] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- include/net/tcp.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -482,17 +482,17 @@ struct sock *cookie_v4_check(struct sock */ static inline void tcp_synq_overflow(struct sock *sk) { - unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp; + unsigned long last_overflow = ACCESS_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp); unsigned long now = jiffies; if (!time_between32(now, last_overflow, last_overflow + HZ)) - tcp_sk(sk)->rx_opt.ts_recent_stamp = now; + ACCESS_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp) = now; } /* syncookies: no recent synqueue overflow on this listening socket? */ static inline bool tcp_synq_no_recent_overflow(const struct sock *sk) { - unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp; + unsigned long last_overflow = ACCESS_ONCE(tcp_sk(sk)->rx_opt.ts_recent_stamp); return time_after(jiffies, last_overflow + TCP_SYNCOOKIE_VALID); }