diff options
| author | Paul Zhang <quic_paulz@quicinc.com> | 2022-10-11 21:04:28 +0800 |
|---|---|---|
| committer | Johannes Berg <johannes.berg@intel.com> | 2022-10-21 12:36:35 +0200 |
| commit | 18429c51c7ff6e6bfd627316c54670230967a7e5 (patch) | |
| tree | 4f323895f7c6f3857da652129623e7d11e0ddff2 /net/wireless/util.c | |
| parent | 57b962e627ec0ae53d4d16d7bd1033e27e67677a (diff) | |
wifi: cfg80211: Fix bitrates overflow issue
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>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Diffstat (limited to 'net/wireless/util.c')
| -rw-r--r-- | net/wireless/util.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/net/wireless/util.c b/net/wireless/util.c index 1f285b515028..39680e7bad45 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; } |