Re: [PATCH net v2] rtnetlink: fix error logic of IFLA_BRIDGE_FLAGS writing back

[Jiri Pirko <jiri@resnulli.us>]

Tue, Feb 27, 2024 at 01:11:28PM CET, linma@zju.edu.cn wrote:
>In the commit d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks
>IFLA_BRIDGE_MODE length"), an adjustment was made to the old loop logic
>in the function `rtnl_bridge_setlink` to enable the loop to also check
>the length of the IFLA_BRIDGE_MODE attribute. However, this adjustment
>removed the `break` statement and led to an error logic of the flags
>writing back at the end of this function.
>
>if (have_flags)
>    memcpy(nla_data(attr), &flags, sizeof(flags));
>    // attr should point to IFLA_BRIDGE_FLAGS NLA !!!
>
>Before the mentioned commit, the `attr` is granted to be IFLA_BRIDGE_FLAGS.
>However, this is not necessarily true fow now as the updated loop will let
>the attr point to the last NLA, even an invalid NLA which could cause
>overflow writes.
>
>This patch introduces a new variable `br_flag` to save the NLA pointer
>that points to IFLA_BRIDGE_FLAGS and uses it to resolve the mentioned
>error logic.
>
>Fixes: d73ef2d69c0d ("rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length")
>Signed-off-by: Lin Ma <linma@zju.edu.cn>
>---
>v1 -> v2: rename the br_flag to br_flags_attr which offers better
>          description suggested by Nikolay.

https://www.kernel.org/doc/html/v6.6/process/maintainer-netdev.html?highlight=network#tl-dr

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