In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix kernel address leakage in atomic cmpxchg's r0 aux reg
The implementation of BPF_CMPXCHG on a high level has the following parameters:
.-[old-val] .-[new-val] BPF_R0 = cmpxchg{32,64}(DST_REG + insn->off, BPF_R0, SRC_REG) `-[mem-loc] `-[old-val]
Given a BPF insn can only have two registers (dst, src), the R0 is fixed and used as an auxilliary register for input (old value) as well as output (returning old value from memory location). While the verifier performs a number of safety checks, it misses to reject unprivileged programs where R0 contains a pointer as old value.
Through brute-forcing it takes about ~16sec on my machine to leak a kernel pointer with BPF_CMPXCHG. The PoC is basically probing for kernel addresses by storing the guessed address into the map slot as a scalar, and using the map value pointer as R0 while SRC_REG has a canary value to detect a matching address.
Fix it by checking R0 for pointers, and reject if that's the case for unprivileged programs.
CVSS Details
- CVSS 3.1 Base Score: 5.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Debian | — | Upgrade linux | Jul 30, 2024 | Jun 19, 2024 |
| Redhat_linux | — | No solution exists | Jul 9, 2025 | Jun 19, 2024 |
| Suse | — | Upgrade kernel-azure-optionalUpgrade kernel-azureUpgrade kernel-rt_debug-vdsoUpgrade kernel-rt_debugUpgrade kernel-devel-azureUpgrade kernel-rt_debug-develUpgrade kernel-rt-livepatch-develUpgrade kernel-syms-rtUpgrade cluster-md-kmp-azureUpgrade kselftests-kmp-azureUpgrade kernel-rt-vdsoUpgrade kselftests-kmp-rtUpgrade kernel-rt-optionalUpgrade kernel-rt-extraUpgrade dlm-kmp-rtUpgrade kernel-azure-extraUpgrade kernel-source-rtUpgrade kernel-azure-livepatch-develUpgrade kernel-source-azureUpgrade reiserfs-kmp-rtUpgrade kernel-azure-vdsoUpgrade kernel-azure-develUpgrade kernel-rt-livepatchUpgrade gfs2-kmp-rtUpgrade kernel-rt-develUpgrade cluster-md-kmp-rtUpgrade kernel-rt_debug-livepatch-develUpgrade kernel-rtUpgrade kernel-devel-rtUpgrade ocfs2-kmp-azureUpgrade gfs2-kmp-azureUpgrade dlm-kmp-azureUpgrade kernel-syms-azureUpgrade reiserfs-kmp-azureUpgrade ocfs2-kmp-rt | Aug 9, 2024 | Jun 19, 2024 |
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