Re: [PATCH net 1/2] ipv4: fix IP ID reuse in ip_select_ident_segs()

[David Ahern <dsahern@kernel.org>]

On 9/29/26 8:12 AM, Eric Dumazet wrote:
> ip_select_ident_segs() must put the first of the @segs reserved IP IDs
> in iph->id, as GSO assigns id, id + 1, ..., id + segs - 1 to segments.
> 
> Commit f866fbc842de ("ipv4: fix data-races around inet->inet_id")
> used atomic_add_return() for non-TCP sockets, which returns the first
> ID of the next packet instead. Consecutive GSO packets can then reuse
> IP IDs.
> 
> SCTP GSO is affected. Other callers use segs == 1, and only see
> a harmless off-by-one (UDP GSO has a separate, older issue, see
> following patch in this series).
> 
> Use atomic_fetch_add() instead, like the TCP path.
> 
> Fixes: f866fbc842de ("ipv4: fix data-races around inet->inet_id")
> Signed-off-by: Eric Dumazet <edumazet@kernel.org>
> ---
>  include/net/ip.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>