CVE-2026-98800: bpf: Wait for an RCU tasks grace period before freeing trampoline progs
In the Linux kernel, the following vulnerability has been resolved:
bpf: Wait for an RCU tasks grace period before freeing trampoline progs
When a prog is detached from a trampoline, it is freed after an RCU grace period, or an RCU tasks trace one if it is sleepable. This covers the tasks that are running the prog, since the prog's enter helper takes the matching read lock before the prog is called. On a preemptible kernel, it doesn't cover a task that was preempted in the trampoline just before the enter helper. That task holds no lock yet, and it calls the prog after it was freed:
BUG: KASAN: vmalloc-out-of-bounds in bpfprogenterrecur+0x3a5/0x3f0 Read of size 8 at addr ffffc90000055040 by task candidate/110 CPU: 1 UID: 0 PID: 110 Comm: candidate Not tainted 7.3.0-rc2-00014-g15071f2a1263-dirty #2 PREEMPT(full) Call Trace: <TASK> bpfprogenterrecur+0x3a5/0x3f0 bpftrampoline6442509193+0x37/0xf1 x64sysfutex+0x9/0x410 dosyscall64+0xb0/0x530 ...
Wait for an RCU tasks grace period before the existing one when freeing a prog that was linked to a trampoline. An RCU tasks grace period only ends once the tasks that were preempted have run again, and bpftrampimageput() already relies on it to free the image. It doesn't wait for tasks that sleep in the trampoline, the next commit takes care of those.
Only progs that were linked to a trampoline can be called this way, so bpftrampolineaddprog() marks them and other progs are still freed as before.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
For BPF programs detached from a trampoline, wait for an RCU tasks grace period before freeing them; use an RCU tasks trace grace period when the trampoline is sleepable.