UBUNTU-CVE-2026-89580: High severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: bpf: Disable preemption in bpfgetstack getperfcallchain() returns a per-CPU perfcallchainentry buffer and releases its recursion slot via putcallchainentry() before returning, so nothing keeps the entry reserved while bpfgetstack() consumes it below. A preemptible BPF program (e.g. a non-sleepable raw tracepoint program on a PREEMPT kernel, which runs under migratedisable() but not preemptdisable()) can be scheduled out between obtaining the entry and the copy. Another task scheduled on the same CPU then reuses the same per-CPU buffer and overwrites trace->nr with a larger value. copylen is then computed from the inflated trace->nr and can exceed the caller's buffer, causing an out-of-bounds write in the memcpy() and in the buildid path. The rcureadlock() taken here alone does not prevent this. It is only taken on the mayfault path, and under CONFIGPREEMPTRCU it does not disable preemption; it merely keeps perf's callchain buffer array alive (freed via callrcu()) and does nothing to stop another task from reusing the entry. Disable preemption around obtaining the callchain entry and copying it into the caller's buffer, so the entry cannot be reused underneath us and trace->nr stays bounded by maxdepth. Build ID resolution may fault and is therefore deferred until after preemption is re-enabled; by then the instruction pointers have already been copied into buf, so it operates only on that private copy. Note, preemptdisable() also subsumes the buffer-lifetime guarantee the rcureadlock() provided, since a preempt-disabled section is an RCU read-side critical section for the callchain buffers' callrcu() reclaim. [ changed Fixes: commit ]