netdev - RE: [PATCH net-next v2] genetlink: fix single op policy dump when do is present

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Message-ID: <CO1PR11MB508906457A3065689598DAC7D63E9@CO1PR11MB5089.namprd11.prod.outlook.com>
Date:   Wed, 9 Nov 2022 20:05:01 +0000
From:   "Keller, Jacob E" <jacob.e.keller@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "Jonathan Lemon" <bsd@...a.com>,
        "leon@...nel.org" <leon@...nel.org>
Subject: RE: [PATCH net-next v2] genetlink: fix single op policy dump when do
 is present



> -----Original Message-----
> From: Jakub Kicinski <kuba@...nel.org>
> Sent: Wednesday, November 9, 2022 10:33 AM
> To: davem@...emloft.net
> Cc: netdev@...r.kernel.org; edumazet@...gle.com; pabeni@...hat.com;
> Jakub Kicinski <kuba@...nel.org>; Jonathan Lemon <bsd@...a.com>; Keller,
> Jacob E <jacob.e.keller@...el.com>; leon@...nel.org
> Subject: [PATCH net-next v2] genetlink: fix single op policy dump when do is
> present
> 
> Jonathan reports crashes when running net-next in Meta's fleet.
> Stats collection uses ethtool -I which does a per-op policy dump
> to check if stats are supported. We don't initialize the dumpit
> information if doit succeeds due to evaluation short-circuiting.
> 
> The crash may look like this:
> 
>    BUG: kernel NULL pointer dereference, address: 0000000000000cc0
>    RIP: 0010:netlink_policy_dump_add_policy+0x174/0x2a0
>      ctrl_dumppolicy_start+0x19f/0x2f0
>      genl_start+0xe7/0x140
> 
> Or we may trigger a warning:
> 
>    WARNING: CPU: 1 PID: 785 at net/netlink/policy.c:87
> netlink_policy_dump_get_policy_idx+0x79/0x80
>    RIP: 0010:netlink_policy_dump_get_policy_idx+0x79/0x80
>      ctrl_dumppolicy_put_op+0x214/0x360
> 
> depending on what garbage we pick up from the stack.
> 

Thanks!

Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>

> Reported-by: Jonathan Lemon <bsd@...a.com>
> Fixes: 26588edbef60 ("genetlink: support split policies in
> ctrl_dumppolicy_put_op()")
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> CC: jacob.e.keller@...el.com
> CC: leon@...nel.org
> 
> v2:
>  - add a helper instead of doing magic sums
>  - improve title
> v1: https://lore.kernel.org/all/20221108204041.330172-1-kuba@kernel.org/
> ---
>  net/netlink/genetlink.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
> index 9b7dfc45dd67..600993c80050 100644
> --- a/net/netlink/genetlink.c
> +++ b/net/netlink/genetlink.c
> @@ -282,6 +282,7 @@ genl_cmd_full_to_split(struct genl_split_ops *op,
>  	return 0;
>  }
> 
> +/* Must make sure that op is initialized to 0 on failure */
>  static int
>  genl_get_cmd(u32 cmd, u8 flags, const struct genl_family *family,
>  	     struct genl_split_ops *op)
> @@ -302,6 +303,21 @@ genl_get_cmd(u32 cmd, u8 flags, const struct
> genl_family *family,
>  	return err;
>  }
> 
> +/* For policy dumping only, get ops of both do and dump.
> + * Fail if both are missing, genl_get_cmd() will zero-init in case of failure.
> + */
> +static int
> +genl_get_cmd_both(u32 cmd, const struct genl_family *family,
> +		  struct genl_split_ops *doit, struct genl_split_ops *dumpit)
> +{
> +	int err1, err2;
> +
> +	err1 = genl_get_cmd(cmd, GENL_CMD_CAP_DO, family, doit);
> +	err2 = genl_get_cmd(cmd, GENL_CMD_CAP_DUMP, family, dumpit);
> +
> +	return err1 && err2 ? -ENOENT : 0;
> +}
> +
>  static bool
>  genl_op_iter_init(const struct genl_family *family, struct genl_op_iter *iter)
>  {
> @@ -1406,10 +1422,10 @@ static int ctrl_dumppolicy_start(struct
> netlink_callback *cb)
>  		ctx->single_op = true;
>  		ctx->op = nla_get_u32(tb[CTRL_ATTR_OP]);
> 
> -		if (genl_get_cmd(ctx->op, GENL_CMD_CAP_DO, rt, &doit) &&
> -		    genl_get_cmd(ctx->op, GENL_CMD_CAP_DUMP, rt, &dump)) {
> +		err = genl_get_cmd_both(ctx->op, rt, &doit, &dump);
> +		if (err) {
>  			NL_SET_BAD_ATTR(cb->extack, tb[CTRL_ATTR_OP]);
> -			return -ENOENT;
> +			return err;
>  		}
> 
>  		if (doit.policy) {
> @@ -1551,13 +1567,9 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct
> netlink_callback *cb)
>  		if (ctx->single_op) {
>  			struct genl_split_ops doit, dumpit;
> 
> -			if (genl_get_cmd(ctx->op, GENL_CMD_CAP_DO,
> -					 ctx->rt, &doit) &&
> -			    genl_get_cmd(ctx->op, GENL_CMD_CAP_DUMP,
> -					 ctx->rt, &dumpit)) {
> -				WARN_ON(1);
> +			if (WARN_ON(genl_get_cmd_both(ctx->op, ctx->rt,
> +						      &doit, &dumpit)))
>  				return -ENOENT;
> -			}
> 
>  			if (ctrl_dumppolicy_put_op(skb, cb, &doit, &dumpit))
>  				return skb->len;
> --
> 2.38.1