| Message ID | 1665493468-24774-1-git-send-email-quic_paulz@quicinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] cfg80211: Fix bitrates overflow issue | expand |
diff --git a/net/wireless/util.c b/net/wireless/util.c index f09d528..59d4947 100644 --- a/net/wireless/util.c +++ b/net/wireless/util.c @@ -1557,10 +1557,12 @@ static u32 cfg80211_calculate_bitrate_eht(struct rate_info *rate) tmp = result; tmp *= SCALE; do_div(tmp, mcs_divisors[rate->mcs]); - result = tmp; /* and take NSS */ - result = (result * rate->nss) / 8; + tmp *= rate->nss; + do_div(tmp, 8); + + result = tmp; return result / 10000; }
When invoking function cfg80211_calculate_bitrate_eht about (320 MHz, EHT-MCS 13, EHT-NSS 2, EHT-GI 0), which means the parameters as flags: 0x80, bw: 7, mcs: 13, eht_gi: 0, nss: 2, this formula (result * rate->nss) will overflow and causes the returned bitrate to be 3959 when it should be 57646. Here is the explanation: u64 tmp; u32 result; … /* tmp = result = 4 * rates_996[0] * = 4 * 480388888 = 0x72889c60 */ tmp = result; /* tmp = 0x72889c60 * 6144 = 0xabccea90000 */ tmp *= SCALE; /* tmp = 0xabccea90000 / mcs_divisors[13] * = 0xabccea90000 / 5120 = 0x8970bba6 */ do_div(tmp, mcs_divisors[rate->mcs]); /* result = 0x8970bba6 */ result = tmp; /* normally (result * rate->nss) = 0x8970bba6 * 2 = 0x112e1774c, * but since result is u32, (result * rate->nss) = 0x12e1774c, * overflow happens and it loses the highest bit. * Then result = 0x12e1774c / 8 = 39595753, */ result = (result * rate->nss) / 8; Signed-off-by: Paul Zhang <quic_paulz@quicinc.com> --- net/wireless/util.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)