CVE-2024-53125: bpf: sync_linked_regs() must preserve subreg_def

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-12-04 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: sync_linked_regs() must preserve subreg_def Range propagation must not affect subreg_def marks, otherwise the following example is rewritten by verifier incorrectly when BPF_F_TEST_RND_HI32 flag is set: 0: call bpf_ktime_get_ns call bpf_ktime_get_ns 1: r0 &= 0x7fffffff after verifier r0 &= 0x7fffffff 2: w1 = w0 rewrites w1 = w0 3: if w0 < 10 goto +0 --------------> r11 = 0x2f5674a6 (r) 4: r1 >>= 32 r11 <<= 32 (r) 5: r0 = r1 r1 |= r11 (r) 6: exit; if w0 < 0xa goto pc+0 r1 >>= 32 r0 = r1 exit (or zero extension of w1 at (2) is missing for architectures that require zero extension for upper register half). The following happens w/o this patch: - r0 is marked as not a subreg at (0); - w1 is marked as subreg at (2); - w1 subreg_def is overridden at (3) by copy_register_state(); - w1 is read at (5) but mark_insn_zext() does not mark (2) for zero extension, because w1 subreg_def is not set; - because of BPF_F_TEST_RND_HI32 flag verifier inserts random value for hi32 bits of (2) (marked (r)); - this random value is read at (5).

Affected products

Linux kernel: from 5.10 before 5.10.232; from 5.11 before 5.15.175; from 5.16 before 6.1.121; from 6.2 before 6.6.67; from 6.7 before 6.11.6; 6.12-rc1, 6.12-rc2, 6.12-rc3 — fixed in 5.10.232, 5.15.175, 6.1.121, 6.11.6, 6.6.67

How to fix

Upgrade to a fixed version: Linux kernel 5.10.232, 5.15.175, 6.1.121, 6.11.6. Check the vendor advisory for mitigations.

References

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