From 60a3a889efe5f56f0ed90059b49d85a6ccfaa2df Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Tue, 9 Nov 2021 10:02:04 +0100 Subject: [PATCH] mac80211: fix radiotap header generation commit c033a38a81bc539d6c0db8c5387e0b14d819a0cf upstream. In commit 8c89f7b3d3f2 ("mac80211: Use flex-array for radiotap header bitmap") we accidentally pointed the position to the wrong place, so we overwrite a present bitmap, and thus cause all kinds of trouble. To see the issue, note that the previous code read: pos = (void *)(it_present + 1); The requirement now is that we need to calculate pos via it_optional, to not trigger the compiler hardening checks, as: pos = (void *)&rthdr->it_optional[...]; Rewriting the original expression, we get (obviously, since that just adds "+ x - x" terms): pos = (void *)(it_present + 1 + rthdr->it_optional - rthdr->it_optional) and moving the "+ rthdr->it_optional" outside to be used as an array: pos = (void *)&rthdr->it_optional[it_present + 1 - rthdr->it_optional]; The original is off by one, fix it. Cc: stable@vger.kernel.org Fixes: 8c89f7b3d3f2 ("mac80211: Use flex-array for radiotap header bitmap") Reported-by: Sid Hayn Signed-off-by: Johannes Berg Tested-by: Sid Hayn Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20211109100203.c61007433ed6.I1dade57aba7de9c4f48d68249adbae62636fd98c@changeid Signed-off-by: Johannes Berg Signed-off-by: Greg Kroah-Hartman --- net/mac80211/rx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c index c4071b0..419f06e 100644 --- a/net/mac80211/rx.c +++ b/net/mac80211/rx.c @@ -364,7 +364,7 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local, * the compiler to think we have walked past the end of the * struct member. */ - pos = (void *)&rthdr->it_optional[it_present - rthdr->it_optional]; + pos = (void *)&rthdr->it_optional[it_present + 1 - rthdr->it_optional]; /* the order of the following fields is important */ -- 2.7.4