netdev - Re: [PATCH v3 net] netlink: Use copy_to_user() for optval in netlink

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Date:   Mon, 24 Apr 2023 09:02:35 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Kuniyuki Iwashima <kuniyu@...zon.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Patrick McHardy <kaber@...sh.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Christophe Ricard <christophe-h.ricard@...com>,
        David Ahern <dsahern@...il.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Brad Spencer <bspencer@...ckberry.com>
Subject: Re: [PATCH v3 net] netlink: Use copy_to_user() for optval in
 netlink_getsockopt().

On Fri, 2023-04-21 at 18:52 +0000, Kuniyuki Iwashima wrote:
> Brad Spencer provided a detailed report [0] that when calling getsockopt()
> for AF_NETLINK, some SOL_NETLINK options set only 1 byte even though such
> options require at least sizeof(int) as length.
> 
> The options return a flag value that fits into 1 byte, but such behaviour
> confuses users who do not initialise the variable before calling
> getsockopt() and do not strictly check the returned value as char.
> 
> Currently, netlink_getsockopt() uses put_user() to copy data to optlen and
> optval, but put_user() casts the data based on the pointer, char *optval.
> As a result, only 1 byte is set to optval.
> 
> To avoid this behaviour, we need to use copy_to_user() or cast optval for
> put_user().
> 
> Note that this changes the behaviour on big-endian systems, but we document
> that the size of optval is int in the man page.
> 
>   $ man 7 netlink
>   ...
>   Socket options
>        To set or get a netlink socket option, call getsockopt(2) to read
>        or setsockopt(2) to write the option with the option level argument
>        set to SOL_NETLINK.  Unless otherwise noted, optval is a pointer to
>        an int.
> 
> Fixes: 9a4595bc7e67 ("[NETLINK]: Add set/getsockopt options to support more than 32 groups")
> Fixes: be0c22a46cfb ("netlink: add NETLINK_BROADCAST_ERROR socket option")
> Fixes: 38938bfe3489 ("netlink: add NETLINK_NO_ENOBUFS socket flag")
> Fixes: 0a6a3a23ea6e ("netlink: add NETLINK_CAP_ACK socket option")
> Fixes: 2d4bc93368f5 ("netlink: extended ACK reporting")
> Fixes: 89d35528d17d ("netlink: Add new socket option to enable strict checking on dumps")
> Reported-by: Brad Spencer <bspencer@...ckberry.com>
> Link: https://lore.kernel.org/netdev/ZD7VkNWFfp22kTDt@datsun.rim.net/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>


Reviewed-by: Johannes Berg <johannes@...solutions.net>

Thanks!

johannes