netdev - Re: [PATCH net] net/netlink: fix NETLINK_LIST_MEMBERSHIPS group array length check

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Date: Fri, 26 May 2023 11:26:41 +0200
From: Simon Horman <simon.horman@...igine.com>
To: Pedro Tammela <pctammela@...atatu.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, kuniyu@...zon.com,
	dh.herrmann@...il.com, jhs@...atatu.com
Subject: Re: [PATCH net] net/netlink: fix NETLINK_LIST_MEMBERSHIPS group
 array length check

On Thu, May 25, 2023 at 11:46:09AM -0300, Pedro Tammela wrote:
> For the socket option 'NETLINK_LIST_MEMBERSHIPS' the length is defined
> as the number of u32 required to represent the whole bitset.
> User space then usually queries the required size and issues a subsequent
> getsockopt call with the correct parameters[1].
> 
> The current code has an unit mismatch between 'len' and 'pos', where
> 'len' is the number of u32 in the passed array while 'pos' is the
> number of bytes iterated in the groups bitset.
> For netlink groups greater than 32, which from a quick glance
> is a rare occasion, the mismatch causes the misreport of groups e.g.
> if a rtnl socket is a member of group 34, it's reported as not a member
> (all 0s).
> 
> [1] https://github.com/systemd/systemd/blob/9c9b9b89151c3e29f3665e306733957ee3979853/src/libsystemd/sd-netlink/netlink-socket.c#L26
> 
> Fixes: b42be38b2778 ("netlink: add API to retrieve all group memberships")
> Signed-off-by: Pedro Tammela <pctammela@...atatu.com>

Reviewed-by: Simon Horman <simon.horman@...igine.com>