netdev - Re: [PATCH net] inet: fix inet_fill

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Date: Fri, 10 May 2024 10:29:42 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, David Ahern
	<dsahern@...nel.org>, <netdev@...r.kernel.org>, <eric.dumazet@...il.com>, "Yu
 Watanabe" <watanabe.yu@...il.com>
Subject: Re: [PATCH net] inet: fix inet_fill_ifaddr() flags truncation

On Fri, May 10, 2024 at 07:29:32AM +0000, Eric Dumazet wrote:
> I missed that (struct ifaddrmsg)->ifa_flags was only 8bits,
> while (struct in_ifaddr)->ifa_flags is 32bits.
> 
> Use a temporary 32bit variable as I did in set_ifa_lifetime()
> and check_lifetime().
> 
> Fixes: 3ddc2231c810 ("inet: annotate data-races around ifa->ifa_flags")
> Reported-by: Yu Watanabe <watanabe.yu@...il.com>
> Dianosed-by: Yu Watanabe <watanabe.yu@...il.com>
> Closes: https://github.com/systemd/systemd/pull/32666#issuecomment-2103977928

Reviewed-by: Larysa Zaremba <larysa.zaremba@...el.com>

> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/ipv4/devinet.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index 7a437f0d41905e6acfdc35743afba3a7abfd0dd5..7e45c34c8340a6d2cf96b4485cd4249fd4da7009 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -1683,6 +1683,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
>  	struct nlmsghdr  *nlh;
>  	unsigned long tstamp;
>  	u32 preferred, valid;
> +	u32 flags;
>  
>  	nlh = nlmsg_put(skb, args->portid, args->seq, args->event, sizeof(*ifm),
>  			args->flags);
> @@ -1692,7 +1693,13 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
>  	ifm = nlmsg_data(nlh);
>  	ifm->ifa_family = AF_INET;
>  	ifm->ifa_prefixlen = ifa->ifa_prefixlen;
> -	ifm->ifa_flags = READ_ONCE(ifa->ifa_flags);
> +
> +	flags = READ_ONCE(ifa->ifa_flags);
> +	/* Warning : ifm->ifa_flags is an __u8, it holds only 8 bits.
> +	 * The 32bit value is given in IFA_FLAGS attribute.
> +	 */
> +	ifm->ifa_flags = (__u8)flags;
> +
>  	ifm->ifa_scope = ifa->ifa_scope;
>  	ifm->ifa_index = ifa->ifa_dev->dev->ifindex;
>  
> @@ -1701,7 +1708,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
>  		goto nla_put_failure;
>  
>  	tstamp = READ_ONCE(ifa->ifa_tstamp);
> -	if (!(ifm->ifa_flags & IFA_F_PERMANENT)) {
> +	if (!(flags & IFA_F_PERMANENT)) {
>  		preferred = READ_ONCE(ifa->ifa_preferred_lft);
>  		valid = READ_ONCE(ifa->ifa_valid_lft);
>  		if (preferred != INFINITY_LIFE_TIME) {
> @@ -1732,7 +1739,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
>  	     nla_put_string(skb, IFA_LABEL, ifa->ifa_label)) ||
>  	    (ifa->ifa_proto &&
>  	     nla_put_u8(skb, IFA_PROTO, ifa->ifa_proto)) ||
> -	    nla_put_u32(skb, IFA_FLAGS, ifm->ifa_flags) ||
> +	    nla_put_u32(skb, IFA_FLAGS, flags) ||
>  	    (ifa->ifa_rt_priority &&
>  	     nla_put_u32(skb, IFA_RT_PRIORITY, ifa->ifa_rt_priority)) ||
>  	    put_cacheinfo(skb, READ_ONCE(ifa->ifa_cstamp), tstamp,
> -- 
> 2.45.0.118.g7fe29c98d7-goog
> 
>