In the Linux kernel, the following vulnerability has been resolved:

net/sched: act_mpls: Fix warning during failed attribute validation

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 its 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: __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

Affected Software

References

• https://git.kernel.org/stable/c/2b157c3c5d6b8ddca48d53c9e662032f65af8d61
• https://git.kernel.org/stable/c/453277feb41c2235cf2c0de9209eef962c401457
• https://git.kernel.org/stable/c/8a97b544b98e44f596219ebb290fd2ba2fd5d644
• https://git.kernel.org/stable/c/9e17f99220d111ea031b44153fdfe364b0024ff2
• https://git.kernel.org/stable/c/9e2c38827cdc6fdd3bb375c8607fc04d289756f9