Subject: Re: [PATCH] cw1200: Revert unnecessary patches that fix unreal use-after-free bugs

From: Kalle Valo <[email-masked]>
Date: Tue, 15 Jun 2021 13:41:33 +0000 (UTC)

Hang Zhang <[email-masked]> wrote:

> A previous commit 4f68ef64cd7f ("cw1200: Fix concurrency 
> use-after-free bugs in cw1200_hw_scan()") tried to fix a seemingly
> use-after-free bug between cw1200_bss_info_changed() and
> cw1200_hw_scan(), where the former frees a sk_buff pointed
> to by frame.skb, and the latter accesses the sk_buff
> pointed to by frame.skb. However, this issue should be a
> false alarm because:
> 
> (1) "frame.skb" is not a shared variable between the above 
> two functions, because "frame" is a local function variable,
> each of the two functions has its own local "frame" - they
> just happen to have the same variable name.
> 
> (2) the sk_buff(s) pointed to by these two "frame.skb" are
> also two different object instances, they are individually
> allocated by different dev_alloc_skb() within the two above
> functions. To free one object instance will not invalidate 
> the access of another different one.
> 
> Based on these facts, the previous commit should be unnecessary.
> Moreover, it also introduced a missing unlock which was 
> addressed in a subsequent commit 51c8d24101c7 ("cw1200: fix missing 
> unlock on error in cw1200_hw_scan()"). Now that the
> original use-after-free is unreal, these two commits should
> be reverted. This patch performs the reversion.
> 
> Fixes: 4f68ef64cd7f ("cw1200: Fix concurrency use-after-free bugs in cw1200_hw_scan()")
> Fixes: 51c8d24101c7 ("cw1200: fix missing unlock on error in cw1200_hw_scan()")
> Signed-off-by: Hang Zhang <[email-masked]>
> Acked-by: Jia-Ju Bai <[email-masked]>

Patch applied to wireless-drivers-next.git, thanks.

3f60f4685699 cw1200: Revert unnecessary patches that fix unreal use-after-free bugs

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