[PATCH] bpf: Fix UAF via mismatching bpf_prog/attachment RCU flavors

[Jann Horn]

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>