diff options
| author | Jiayuan Chen <jiayuan.chen@linux.dev> | 2026-10-08 17:26:36 +0800 |
|---|---|---|
| committer | Paolo Abeni <pabeni@redhat.com> | 2026-10-13 15:17:55 +0200 |
| commit | 7d52b5d16afc1cf8484ae321658e217a80e3ff4d (patch) | |
| tree | eb39790e4c7b5a13750633418c9cb44f6b077a26 /net/ipv4 | |
| parent | f09eb97322b16a6f709a47599c95b62f786905f9 (diff) | |
tcp_cubic: fix divide by zero and endless loop on bad module params
beta_scale and cube_factor are computed once at module init, and
beta == 1024 or bic_scale == 0 is a divide by zero right there. Other
out of range values give garbage: negative beta can make beta_scale 0,
and bic_scale * 10 can overflow. Reject them. Read beta once, as it
can be written through sysfs before the init function runs.
A small beta also gives a small beta_scale, and (cwnd * beta_scale) >> 3
truncates to 0 for a tiny cwnd, so the TCP friendliness loop never
ends. Rather than testing delta on every ACK, make sure beta_scale is
at least 8 at init, so delta is >= 1 within the cwnd < 1 million
packets limit this code is designed for. This slows the TCP friendly
estimate for beta < 512, a backoff harder than Reno's 0.5, which is
not a setting anyone should use.
Fixes: df3271f3361b ("[TCP] BIC: CUBIC window growth (2.0)")
Suggested-by: Eric Dumazet <edumazet@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@kernel.org>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://patch.msgid.link/20261008092641.140777-4-jiayuan.chen@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/tcp_cubic.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index 119bf8cbb007..a88e4bf86150 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -500,16 +500,26 @@ static const struct btf_kfunc_id_set tcp_cubic_kfunc_set = { static int __init cubictcp_register(void) { + int b = READ_ONCE(beta); int ret; BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); + if (b < 0 || b >= BICTCP_BETA_SCALE || + bic_scale <= 0 || bic_scale > INT_MAX / 10) { + pr_err("tcp_cubic: invalid beta %d or bic_scale %d\n", + b, bic_scale); + return -EINVAL; + } + /* Precompute a bunch of the scaling factors that are used per-packet * based on SRTT of 100ms */ - beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3 - / (BICTCP_BETA_SCALE - beta); + beta_scale = 8 * (BICTCP_BETA_SCALE + b) / 3 + / (BICTCP_BETA_SCALE - b); + /* bictcp_update() needs (cwnd * beta_scale) >> 3 to be >= 1 */ + beta_scale = max(beta_scale, 8U); cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ |