Bug 2516491 (CVE-2026-72427)

Summary: CVE-2026-72427 kernel: bpf: Fix effective prog array index with BPF_F_PREORDER
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's BPF (Berkeley Packet Filter) cgroup program handling. Incorrect indexing in the `replace_effective_prog()` and `purge_effective_progs()` functions, particularly when `BPF_F_PREORDER` programs are active, can lead to memory corruption. This issue can result in overwriting incorrect memory slots or a use-after-free condition, where the system attempts to access memory that has already been deallocated.
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Description OSIDB Bzimport 2026-08-15 06:15:18 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix effective prog array index with BPF_F_PREORDER

replace_effective_prog() and purge_effective_progs() located the slot in
the effective array by walking the program hlist and counting entries
linearly. That count does not match the array layout: compute_effective_
progs() places BPF_F_PREORDER programs at the front (ancestor cgroup
first, attach order within a cgroup) and the rest after them (descendant
cgroup first). So when a preorder program is present, the linear hlist
position no longer equals the program's index in the effective array.

For replace_effective_prog() (bpf_link_update()) this overwrote the
wrong slot, corrupting the effective order. For purge_effective_progs(),
it could dummy out a slot belonging to a different program and leave the
detached program in the array while bpf_prog_put() drops its reference,
i.e. a use-after-free.

Fix both by replaying compute_effective_progs()'s placement (including
the per-cgroup preorder reversal) in a shared effective_prog_pos()
helper. Identify the entry by its struct bpf_prog_list pointer rather
than by (prog, link) value, so the lookup resolves to exactly the
attachment the syscall selected even when the same bpf_prog is attached
to several cgroups in the hierarchy.
Comment 1 gkamathe 2026-08-18 13:50:06 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081526-CVE-2026-72427-ea61@gregkh/T