Description

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 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:

__netlink_policy_dump_write_attr+0x23d...

Classification

CVE ID: CVE-2023-52906

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 5.08% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

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

Timeline