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: stable@xxxxxxxxxxxxxxx
Fixes: 8c7dcb84e3b7 ("bpf: implement sleepable uprobes by chaining gps")
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
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 <jannh@xxxxxxxxxx>
