[PATCH] ipv6: Use local variable for ifa->flags in inet6_fill_ifaddr

[PATCH] ipv6: Use local variable for ifa->flags in inet6_fill_ifaddr

[Zilin Guan]

Currently, the inet6_fill_ifaddr() function reads the value of ifa->flags
using READ_ONCE() and stores it in the local variable flags. However,
the subsequent call to put_ifaddrmsg() uses ifa->flags again instead of
the already read local variable. This re-read is unnecessary because
no other thread can modify ifa->flags between the initial READ_ONCE()
and the subsequent use in put_ifaddrmsg().

Signed-off-by: Zilin Guan <zilinguan811@gmail.com>
---
 net/ipv6/addrconf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 94dceac52884..c4b080471b39 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5143,7 +5143,7 @@ static int inet6_fill_ifaddr(struct sk_buff *skb,
 		return -EMSGSIZE;
 
 	flags = READ_ONCE(ifa->flags);
-	put_ifaddrmsg(nlh, ifa->prefix_len, ifa->flags, rt_scope(ifa->scope),
+	put_ifaddrmsg(nlh, ifa->prefix_len, flags, rt_scope(ifa->scope),
 		      ifa->idev->dev->ifindex);
 
 	if (args->netnsid >= 0 &&
-- 
2.34.1

Re: [PATCH] ipv6: Use local variable for ifa->flags in inet6_fill_ifaddr

[Eric Dumazet]

On Mon, Nov 4, 2024 at 2:25 PM Zilin Guan <zilinguan811@gmail.com> wrote:
>
> Currently, the inet6_fill_ifaddr() function reads the value of ifa->flags
> using READ_ONCE() and stores it in the local variable flags. However,
> the subsequent call to put_ifaddrmsg() uses ifa->flags again instead of
> the already read local variable. This re-read is unnecessary because
> no other thread can modify ifa->flags between the initial READ_ONCE()
> and the subsequent use in put_ifaddrmsg().

I do not think this last sentence is true. I would rephrase this or remove it.

Otherwise, patch looks fine to me, thanks.


>
> Signed-off-by: Zilin Guan <zilinguan811@gmail.com>
> ---
>  net/ipv6/addrconf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 94dceac52884..c4b080471b39 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -5143,7 +5143,7 @@ static int inet6_fill_ifaddr(struct sk_buff *skb,
>                 return -EMSGSIZE;
>
>         flags = READ_ONCE(ifa->flags);
> -       put_ifaddrmsg(nlh, ifa->prefix_len, ifa->flags, rt_scope(ifa->scope),
> +       put_ifaddrmsg(nlh, ifa->prefix_len, flags, rt_scope(ifa->scope),
>                       ifa->idev->dev->ifindex);
>
>         if (args->netnsid >= 0 &&
> --
> 2.34.1
>