[openwrt/openwrt] mac80211: fix a regression in generating radiotap headers

[LEDE Commits]

nbd pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/b92a9f607b9af049c8e91a961947b0b10ea253a0

commit b92a9f607b9af049c8e91a961947b0b10ea253a0
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Fri Nov 26 08:42:25 2021 +0100

    mac80211: fix a regression in generating radiotap headers
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 ...8-mac80211-fix-radiotap-header-generation.patch | 49 ++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/package/kernel/mac80211/patches/subsys/308-mac80211-fix-radiotap-header-generation.patch b/package/kernel/mac80211/patches/subsys/308-mac80211-fix-radiotap-header-generation.patch
new file mode 100644
index 0000000000..a408c3d802
--- /dev/null
+++ b/package/kernel/mac80211/patches/subsys/308-mac80211-fix-radiotap-header-generation.patch
@@ -0,0 +1,49 @@
+From: Johannes Berg <johannes.berg at intel.com>
+Date: Tue, 9 Nov 2021 10:02:04 +0100
+Subject: [PATCH] mac80211: fix radiotap header generation
+
+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 at vger.kernel.org
+Fixes: 8c89f7b3d3f2 ("mac80211: Use flex-array for radiotap header bitmap")
+Reported-by: Sid Hayn <sidhayn at gmail.com>
+Signed-off-by: Johannes Berg <johannes.berg at intel.com>
+Tested-by: Sid Hayn <sidhayn at gmail.com>
+Reviewed-by: Kees Cook <keescook at chromium.org>
+Link: https://lore.kernel.org/r/20211109100203.c61007433ed6.I1dade57aba7de9c4f48d68249adbae62636fd98c@changeid
+Signed-off-by: Johannes Berg <johannes.berg at intel.com>
+---
+
+--- a/net/mac80211/rx.c
++++ b/net/mac80211/rx.c
+@@ -364,7 +364,7 @@ ieee80211_add_rx_radiotap_header(struct
+ 	 * 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 */
+