[PATCH net] neighbour: fix unaligned access to pneigh_entry

[PATCH net] neighbour: fix unaligned access to pneigh_entry

[Qingfang DENG]

From: Qingfang DENG <qingfang.deng@siflower.com.cn>

After the blamed commit, the member key is longer 4-byte aligned. On
platforms that do not support unaligned access, e.g., MIPS32R2 with
unaligned_action set to 2, this will trigger a crash when accessing
an IPv6 pneigh_entry, as the key is cast to an in6_addr pointer.

Align the member to 4 bytes on said platforms.

Fixes: 62dd93181aaa ("[IPV6] NDISC: Set per-entry is_router flag in Proxy NA.")
Signed-off-by: Qingfang DENG <qingfang.deng@siflower.com.cn>
---
 include/net/neighbour.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 3fa5774bddac..c0195ed9d111 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -180,7 +180,11 @@ struct pneigh_entry {
 	netdevice_tracker	dev_tracker;
 	u32			flags;
 	u8			protocol;
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	u8			key[];
+#else
+	u8			key[] __aligned(4);
+#endif
 };
 
 /*
-- 
2.34.1

Re: [PATCH net] neighbour: fix unaligned access to pneigh_entry

[Jakub Kicinski]

On Wed, 31 May 2023 18:42:33 +0800 Qingfang DENG wrote:
> +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>  	u8			key[];
> +#else
> +	u8			key[] __aligned(4);
> +#endif

I'd appreciate a second opinion, but to me it's very unlikely we'd save
any memory even with efficient aligned access here. No reasonably key
will fit into 3 bytes, right? So we can as well avoid the ifdef and
make the key[] always aligned. Or preferably, if it doesn't cause
compilation issues, make the type of the key u32?

Re: [PATCH net] neighbour: fix unaligned access to pneigh_entry

[Eric Dumazet]

On Wed, May 31, 2023 at 8:16 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 31 May 2023 18:42:33 +0800 Qingfang DENG wrote:
> > +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> >       u8                      key[];
> > +#else
> > +     u8                      key[] __aligned(4);
> > +#endif
>
> I'd appreciate a second opinion, but to me it's very unlikely we'd save
> any memory even with efficient aligned access here. No reasonably key
> will fit into 3 bytes, right? So we can as well avoid the ifdef and
> make the key[] always aligned. Or preferably, if it doesn't cause
> compilation issues, make the type of the key u32?

Same feeling, we could avoid the CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS ifdef.

[PATCH net v2] neighbour: fix unaligned access to pneigh_entry

[Qingfang DENG]

From: Qingfang DENG <qingfang.deng@siflower.com.cn>

After the blamed commit, the member key is longer 4-byte aligned. On
platforms that do not support unaligned access, e.g., MIPS32R2 with
unaligned_action set to 1, this will trigger a crash when accessing
an IPv6 pneigh_entry, as the key is cast to an in6_addr pointer.

Change the type of the key to u32 to make it aligned.

Fixes: 62dd93181aaa ("[IPV6] NDISC: Set per-entry is_router flag in Proxy NA.")
Signed-off-by: Qingfang DENG <qingfang.deng@siflower.com.cn>
---
v2: remove the ifdef, and use u32 type

 include/net/neighbour.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 3fa5774bddac..f6a8ecc6b1fa 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -180,7 +180,7 @@ struct pneigh_entry {
 	netdevice_tracker	dev_tracker;
 	u32			flags;
 	u8			protocol;
-	u8			key[];
+	u32			key[];
 };
 
 /*
-- 
2.34.1

Re: [PATCH net v2] neighbour: fix unaligned access to pneigh_entry

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  1 Jun 2023 09:54:32 +0800 you wrote:
> From: Qingfang DENG <qingfang.deng@siflower.com.cn>
> 
> After the blamed commit, the member key is longer 4-byte aligned. On
> platforms that do not support unaligned access, e.g., MIPS32R2 with
> unaligned_action set to 1, this will trigger a crash when accessing
> an IPv6 pneigh_entry, as the key is cast to an in6_addr pointer.
> 
> [...]

Here is the summary with links:
  - [net,v2] neighbour: fix unaligned access to pneigh_entry
    https://git.kernel.org/netdev/net/c/ed779fe4c9b5

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html