From 7d0d673627e20cfa3b21a829a896ce03b58a4f1c Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Tue, 10 Dec 2024 20:08:14 +0100 Subject: bpf: Fix theoretical prog_array UAF in __uprobe_perf_func() Currently, the pointer stored in call->prog_array is loaded in __uprobe_perf_func(), with no RCU annotation and no immediately visible RCU protection, so it looks as if the loaded pointer can immediately be dangling. Later, bpf_prog_run_array_uprobe() starts a RCU-trace read-side critical section, but this is too late. It then uses rcu_dereference_check(), but this use of rcu_dereference_check() does not actually dereference anything. Fix it by aligning the semantics to bpf_prog_run_array(): Let the caller provide rcu_read_lock_trace() protection and then load call->prog_array with rcu_dereference_check(). This issue seems to be theoretical: I don't know of any way to reach this code without having handle_swbp() further up the stack, which is already holding a rcu_read_lock_trace() lock, so where we take rcu_read_lock_trace() in __uprobe_perf_func()/bpf_prog_run_array_uprobe() doesn't actually have any effect. Fixes: 8c7dcb84e3b7 ("bpf: implement sleepable uprobes by chaining gps") Suggested-by: Andrii Nakryiko Signed-off-by: Jann Horn Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20241210-bpf-fix-uprobe-uaf-v4-1-5fc8959b2b74@google.com --- kernel/trace/trace_uprobe.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'kernel/trace/trace_uprobe.c') diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index fed382b7881b..4875e7f5de3d 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -1402,9 +1402,13 @@ static void __uprobe_perf_func(struct trace_uprobe *tu, #ifdef CONFIG_BPF_EVENTS if (bpf_prog_array_valid(call)) { + const struct bpf_prog_array *array; u32 ret; - ret = bpf_prog_run_array_uprobe(call->prog_array, regs, bpf_prog_run); + rcu_read_lock_trace(); + array = rcu_dereference_check(call->prog_array, rcu_read_lock_trace_held()); + ret = bpf_prog_run_array_uprobe(array, regs, bpf_prog_run); + rcu_read_unlock_trace(); if (!ret) return; } -- cgit v1.2.3