[PATCH v2] wifi: iwlegacy: 3945-rs: fix possible null-pointer dereferences in il3945_rs_get_rate()

[Tuo Li <islituo@gmail.com>]

In this function, il_sta is assigned to rs_sta, and rs_sta is dereferenced
at several points. If il_sta is NULL, this can lead to null-pointer
dereferences. To fix this issue, add an early check for il_sta and return
if it is NULL, consistent with the handling in il3945_rs_tx_status().

Besides, if the STA il data is uninitialized, return early instead of
setting il_sta to NULL, consistent with the handling in
il3945_rs_tx_status().

Signed-off-by: Tuo Li <islituo@gmail.com>
---
v2:
* Return early for uninitialized STA il data and align D_RATE messages with
  il3945_rs_tx_status(). Add a wifi: prefix to the patch title.
  Thanks to Stanislaw Gruszka for the helpful advice.
---
 drivers/net/wireless/intel/iwlegacy/3945-rs.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlegacy/3945-rs.c b/drivers/net/wireless/intel/iwlegacy/3945-rs.c
index 1826c37c090c..c509c89bba00 100644
--- a/drivers/net/wireless/intel/iwlegacy/3945-rs.c
+++ b/drivers/net/wireless/intel/iwlegacy/3945-rs.c
@@ -626,10 +626,15 @@ il3945_rs_get_rate(void *il_r, struct ieee80211_sta *sta, void *il_sta,
 
 	D_RATE("enter\n");
 
+	if (!il_sta) {
+		D_RATE("leave: No STA il data to update!\n");
+		return;
+	}
+
 	/* Treat uninitialized rate scaling data same as non-existing. */
-	if (rs_sta && !rs_sta->il) {
-		D_RATE("Rate scaling information not initialized yet.\n");
-		il_sta = NULL;
+	if (!rs_sta->il) {
+		D_RATE("leave: STA il data uninitialized!\n");
+		return;
 	}
 
 	rate_mask = sta->deflink.supp_rates[sband->band];
-- 
2.43.0