diff mbox series

[1/2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug

Message ID 20210816085128.10931-1-pkshih@realtek.com (mailing list archive)
State Changes Requested
Delegated to: Johannes Berg
Headers show
Series [1/2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug | expand

Commit Message

Ping-Ke Shih Aug. 16, 2021, 8:51 a.m. UTC 
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: Ping-Ke Shih <pkshih@realtek.com>
---
 net/mac80211/tx.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Felix Fietkau Aug. 16, 2021, 12:22 p.m. UTC | #1 
On 2021-08-16 10:51, Ping-Ke Shih wrote:
> 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.
I think instead of iterating over fragments a second time, we should
move the ieee80211_amsdu_prepare_head call further up.

- Felix
Ping-Ke Shih Aug. 30, 2021, 6:27 a.m. UTC | #2 
> -----Original Message-----
> From: Felix Fietkau [mailto:nbd@nbd.name]
> Sent: Monday, August 16, 2021 8:23 PM
> To: Pkshih; johannes@sipsolutions.net
> Cc: linux-wireless@vger.kernel.org; Gary Chang
> Subject: Re: [PATCH 1/2] mac80211: Fix ieee80211_amsdu_aggregate frag_tail bug
> 
> On 2021-08-16 10:51, Ping-Ke Shih wrote:
> > 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.
> I think instead of iterating over fragments a second time, we should
> move the ieee80211_amsdu_prepare_head call further up.
> 

The first iteration is used to calculate 'n' and 'nfrags' to decide if
we need to do AMSDU as well as ieee80211_amsdu_prepare_head(), so we
don't have a good idea to move the function upward. However, we have
an alternative idea [1] to fix frag_tail. 

[1] https://lore.kernel.org/linux-wireless/20210830061728.10332-1-pkshih@realtek.com/T/#u

--
Ping-Ke
diff mbox series

Patch

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 8509778ff31f..9e0d4fca1c76 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -3406,6 +3406,12 @@  static bool ieee80211_amsdu_aggregate(struct ieee80211_sub_if_data *sdata,
 
 	head->len += skb->len;
 	head->data_len += skb->len;
+
+	/* frag_list should be updated after pskb_expand_head() */
+	frag_tail = &skb_shinfo(head)->frag_list;
+	while (*frag_tail)
+		frag_tail = &(*frag_tail)->next;
+
 	*frag_tail = skb;
 
 out_recalc: