beta_scale and cube_factor are computed once at module init, and they
need 1024 - beta and bic_scale * 10 to be positive: beta == 1024 or
bic_scale == 0 crash right there, beta > 1024 or a negative bic_scale
gives garbage or wraps to 0. Negative beta can also make beta_scale 0.
Reject them.
A small beta also gives a small beta_scale, and (cwnd * scale) >> 3
truncates to 0 for a tiny cwnd (e.g. 2), so the TCP friendliness loop
never ends. Clamp delta to 1.
Fixes: df3271f3361b ("[TCP] BIC: CUBIC window growth (2.0)")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
---
Target net-next since it is not a big problem.
---
net/ipv4/tcp_cubic.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 119bf8cbb007c..2f04dca5be095 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -298,7 +298,7 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked)
if (tcp_friendliness) {
u32 scale = beta_scale;
- delta = (cwnd * scale) >> 3;
+ delta = max((cwnd * scale) >> 3, 1U);
while (ca->ack_cnt > delta) { /* update tcp cwnd */
ca->ack_cnt -= delta;
ca->tcp_cwnd++;@@ -504,6 +504,11 @@ static int __init cubictcp_register(void)
BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
+ if (beta < 0 || beta >= BICTCP_BETA_SCALE || bic_scale <= 0) {
+ pr_err("tcp_cubic: invalid beta %d or bic_scale %d\n", beta, bic_scale);
+ return -EINVAL;
+ }
+
/* Precompute a bunch of the scaling factors that are used per-packet
* based on SRTT of 100ms
*/--
2.43.0