Uprobes always use bpf_prog_run_array_uprobe() under tasks-trace-RCU protection. But it is possible to attach a non-sleepable BPF program to a uprobe, and non-sleepable BPF programs are freed via normal RCU (see __bpf_prog_put_noref()). This leads to UAF of the bpf_prog because a normal RCU grace period does not imply a tasks-trace-RCU grace period.
Fix it by explicitly waiting for a tasks-trace-RCU grace period after removing the attachment of a bpf_prog to a perf_event. Cc: [email protected] Fixes: 8c7dcb84e3b7 ("bpf: implement sleepable uprobes by chaining gps") Suggested-by: Andrii Nakryiko <[email protected]> Suggested-by: Alexei Starovoitov <[email protected]> Signed-off-by: Jann Horn <[email protected]> --- kernel/trace/bpf_trace.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 949a3870946c381820e8fa7194851b84593d17d9..a403b05a7091384fb08e8c47ed02fad79c1a4874 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2258,6 +2258,13 @@ void perf_event_detach_bpf_prog(struct perf_event *event) bpf_prog_array_free_sleepable(old_array); } + /* + * It could be that the bpf_prog is not sleepable (and will be freed + * via normal RCU), but is called from a point that supports sleepable + * programs and uses tasks-trace-RCU. + */ + synchronize_rcu_tasks_trace(); + bpf_prog_put(event->prog); event->prog = NULL; --- base-commit: 509df676c2d79c985ec2eaa3e3a3bbe557645861 change-id: 20241210-bpf-fix-actual-uprobe-uaf-0aa234c0e005 -- Jann Horn <[email protected]>
