[PATCH v2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug

[PATCH v2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug

[Ping-Ke Shih]

From: Chih-Kang Chang <gary.chang@realtek.com>

In ieee80211_amsdu_aggregate() set a pointer frag_tail point to the
end of skb_shinfo(head)->frag_list, and use it to bind other skb in
the end of this function. But when execute ieee80211_amsdu_aggregate()
->ieee80211_amsdu_realloc_pad()->pskb_expand_head(), the address of
skb_shinfo(head)->frag_list will be changed. However, the
ieee80211_amsdu_aggregate() not update frag_tail after call
pskb_expand_head(). That will cause the second skb can't bind to the
head skb appropriately.So we update the address of frag_tail to fix it.

Fixes: 6e0456b54545 ("mac80211: add A-MSDU tx support")
Signed-off-by: Chih-Kang Chang <gary.chang@realtek.com>
Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
---
v2: an alternative fix to prevent iterating fragment twice.
---
 net/mac80211/tx.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 2d1193ed3eb5..fb5e43489b62 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3380,6 +3380,13 @@ static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
 	if (!ieee80211_amsdu_prepare_head(sdata, fast_tx, head))
 		goto out;
 
+       /* While n == 2, frag_tail should be the address of head's frag_list.
+	* However, head probably re-alloc after ieee80211_amsdu_prepare_head.
+	* So, re-assign frag_tail again to make sure the correctness.
+	*/
+	if (n == 2)
+		frag_tail = &skb_shinfo(head)->frag_list;
+
 	/*
 	 * Pad out the previous subframe to a multiple of 4 by adding the
 	 * padding to the next one, that's being added. Note that head->len
-- 
2.25.1

RE: [PATCH v2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug

[Pkshih]

> -----Original Message-----
> From: Ping-Ke Shih [mailto:pkshih@realtek.com]
> Sent: Monday, August 30, 2021 2:17 PM
> To: johannes@sipsolutions.net
> Cc: linux-wireless@vger.kernel.org; nbd@nbd.name; Gary Chang; Kevin Yang
> Subject: [PATCH v2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug
> 
> From: Chih-Kang Chang <gary.chang@realtek.com>
> 
> In ieee80211_amsdu_aggregate() set a pointer frag_tail point to the
> end of skb_shinfo(head)->frag_list, and use it to bind other skb in
> the end of this function. But when execute ieee80211_amsdu_aggregate()
> ->ieee80211_amsdu_realloc_pad()->pskb_expand_head(), the address of
> skb_shinfo(head)->frag_list will be changed. However, the
> ieee80211_amsdu_aggregate() not update frag_tail after call
> pskb_expand_head(). That will cause the second skb can't bind to the
> head skb appropriately.So we update the address of frag_tail to fix it.
> 
> Fixes: 6e0456b54545 ("mac80211: add A-MSDU tx support")
> Signed-off-by: Chih-Kang Chang <gary.chang@realtek.com>
> Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
> Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
> ---
> v2: an alternative fix to prevent iterating fragment twice.
> ---
>  net/mac80211/tx.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index 2d1193ed3eb5..fb5e43489b62 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -3380,6 +3380,13 @@ static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
>  	if (!ieee80211_amsdu_prepare_head(sdata, fast_tx, head))
>  		goto out;
> 
> +       /* While n == 2, frag_tail should be the address of head's frag_list.
> +	* However, head probably re-alloc after ieee80211_amsdu_prepare_head.
> +	* So, re-assign frag_tail again to make sure the correctness.
> +	*/
> +	if (n == 2)
> +		frag_tail = &skb_shinfo(head)->frag_list;
> +

I mess up the coding style and fix it by v3 [1]. Please ignore this patch.

[1] https://lore.kernel.org/linux-wireless/20210830073240.12736-1-pkshih@realtek.com/T/#u

--
Ping-Ke