netdev - Re: [PATCH net] net/sched: act_mpls: Fix warning during failed attribute validation

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Date:   Mon, 09 Jan 2023 17:08:10 -0800
From:   Alexander H Duyck <alexander.duyck@...il.com>
To:     Ido Schimmel <idosch@...dia.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, willemb@...gle.com, simon.horman@...ronome.com,
        john.hurley@...ronome.com, harperchen1110@...il.com,
        johannes@...solutions.net
Subject: Re: [PATCH net] net/sched: act_mpls: Fix warning during failed
 attribute validation

On Sat, 2023-01-07 at 19:10 +0200, Ido Schimmel wrote:
> The 'TCA_MPLS_LABEL' attribute is of 'NLA_U32' type, but has a
> validation type of 'NLA_VALIDATE_FUNCTION'. This is an invalid
> combination according to the comment above 'struct nla_policy':
> 
> "
> Meaning of `validate' field, use via NLA_POLICY_VALIDATE_FN:
>    NLA_BINARY           Validation function called for the attribute.
>    All other            Unused - but note that it's a union
> "
> 
> This can trigger the warning [1] in nla_get_range_unsigned() when
> validation of the attribute fails. Despite being of 'NLA_U32' type, the
> associated 'min'/'max' fields in the policy are negative as they are
> aliased by the 'validate' field.
> 
> Fix by changing the attribute type to 'NLA_BINARY' which is consistent
> with the above comment and all other users of NLA_POLICY_VALIDATE_FN().
> As a result, move the length validation to the validation function.
> 
> No regressions in MPLS tests:
> 
>  # ./tdc.py -f tc-tests/actions/mpls.json
>  [...]
>  # echo $?
>  0
> 
> [1]
> WARNING: CPU: 0 PID: 17743 at lib/nlattr.c:118
> nla_get_range_unsigned+0x1d8/0x1e0 lib/nlattr.c:117
> Modules linked in:
> CPU: 0 PID: 17743 Comm: syz-executor.0 Not tainted 6.1.0-rc8 #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014
> RIP: 0010:nla_get_range_unsigned+0x1d8/0x1e0 lib/nlattr.c:117
> [...]
> Call Trace:
>  <TASK>
>  __netlink_policy_dump_write_attr+0x23d/0x990 net/netlink/policy.c:310
>  netlink_policy_dump_write_attr+0x22/0x30 net/netlink/policy.c:411
>  netlink_ack_tlv_fill net/netlink/af_netlink.c:2454 [inline]
>  netlink_ack+0x546/0x760 net/netlink/af_netlink.c:2506
>  netlink_rcv_skb+0x1b7/0x240 net/netlink/af_netlink.c:2546
>  rtnetlink_rcv+0x18/0x20 net/core/rtnetlink.c:6109
>  netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
>  netlink_unicast+0x5e9/0x6b0 net/netlink/af_netlink.c:1345
>  netlink_sendmsg+0x739/0x860 net/netlink/af_netlink.c:1921
>  sock_sendmsg_nosec net/socket.c:714 [inline]
>  sock_sendmsg net/socket.c:734 [inline]
>  ____sys_sendmsg+0x38f/0x500 net/socket.c:2482
>  ___sys_sendmsg net/socket.c:2536 [inline]
>  __sys_sendmsg+0x197/0x230 net/socket.c:2565
>  __do_sys_sendmsg net/socket.c:2574 [inline]
>  __se_sys_sendmsg net/socket.c:2572 [inline]
>  __x64_sys_sendmsg+0x42/0x50 net/socket.c:2572
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Link: https://lore.kernel.org/netdev/CAO4mrfdmjvRUNbDyP0R03_DrD_eFCLCguz6OxZ2TYRSv0K9gxA@mail.gmail.com/
> Fixes: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
> Reported-by: Wei Chen <harperchen1110@...il.com>
> Tested-by: Wei Chen <harperchen1110@...il.com>
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> ---
>  net/sched/act_mpls.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sched/act_mpls.c b/net/sched/act_mpls.c
> index ff47ce4d3968..6b26bdb999d7 100644
> --- a/net/sched/act_mpls.c
> +++ b/net/sched/act_mpls.c
> @@ -134,6 +134,11 @@ static int valid_label(const struct nlattr *attr,
>  {
>  	const u32 *label = nla_data(attr);
>  
> +	if (nla_len(attr) != sizeof(*label)) {
> +		NL_SET_ERR_MSG_MOD(extack, "Invalid MPLS label length");
> +		return -EINVAL;
> +	}
> +
>  	if (*label & ~MPLS_LABEL_MASK || *label == MPLS_LABEL_IMPLNULL) {
>  		NL_SET_ERR_MSG_MOD(extack, "MPLS label out of range");
>  		return -EINVAL;
> @@ -145,7 +150,8 @@ static int valid_label(const struct nlattr *attr,
>  static const struct nla_policy mpls_policy[TCA_MPLS_MAX + 1] = {
>  	[TCA_MPLS_PARMS]	= NLA_POLICY_EXACT_LEN(sizeof(struct tc_mpls)),
>  	[TCA_MPLS_PROTO]	= { .type = NLA_U16 },
> -	[TCA_MPLS_LABEL]	= NLA_POLICY_VALIDATE_FN(NLA_U32, valid_label),
> +	[TCA_MPLS_LABEL]	= NLA_POLICY_VALIDATE_FN(NLA_BINARY,
> +							 valid_label),
>  	[TCA_MPLS_TC]		= NLA_POLICY_RANGE(NLA_U8, 0, 7),
>  	[TCA_MPLS_TTL]		= NLA_POLICY_MIN(NLA_U8, 1),
>  	[TCA_MPLS_BOS]		= NLA_POLICY_RANGE(NLA_U8, 0, 1),

Looks good to me.

Reviewed-by: Alexander Duyck <alexanderduyck@...com>