CVE-2026-98047: bpf: Check ancestor frames for rbtree callbacks
In the Linux kernel, the following vulnerability has been resolved:
bpf: Check ancestor frames for rbtree callbacks
bpfrbtreeadd() invokes its comparator while the caller holds the root lock. The native insertion code retains raw parent and link pointers across the callback, so the verifier prohibits unlocking, consuming tree nodes, or changing RCU state from that callback.
inrbtreelockrequiredcb() only checks the innermost verifier frame. Static subprogram calls are permitted while holding a spin lock, and such a call pushes a frame without incallbackfn set. Consequently, all callback restrictions disappear in the nested frame. The subprogram can unlock the tree, remove and drop the node being compared, then relock. Native insertion resumes with the stale parent pointer and links freed memory into the tree.
Walk all active frames for the rbtree callback instead. Benign static subprograms remain permitted, while callback restrictions follow execution into nested frames.
Affected Software
Event History
Frequently Asked Questions
What conditions are required to exploit this issue?
Exploitation requires a BPF rbtree comparator callback that makes a static subprogram call while the rbtree root lock is held. The nested subprogram must then unlock the tree, remove and release the node being compared, and relock the tree before native insertion resumes.
What is the consequence of a successful exploit?
The native rbtree insertion code can resume using stale parent and link pointers after the compared node has been freed. This can cause freed memory to be linked into the tree.
How does the fix prevent the issue?
The fix checks all active verifier frames for rbtree callback context rather than only the innermost frame. This preserves callback restrictions in nested static subprogram calls while continuing to allow benign static subprograms under the lock.