[PATCH bpf-next v3 04/12] bpf: Ensure RCU lock is held around bpf_prog_ksym_find

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add a warning to ensure RCU lock is held around tree lookup, and then
fix one of the invocations in bpf_stack_walker. The program has an
active stack frame and won't disappear.

Fixes: f18b03fabaa9 ("bpf: Implement BPF exceptions")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/core.c    | 5 ++++-
 kernel/bpf/helpers.c | 2 ++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 5c6e9fbb5508..b4203f68cf33 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -782,7 +782,10 @@ bool is_bpf_text_address(unsigned long addr)
 
 struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
 {
-	struct bpf_ksym *ksym = bpf_ksym_find(addr);
+	struct bpf_ksym *ksym;
+
+	WARN_ON_ONCE(!rcu_read_lock_held());
+	ksym = bpf_ksym_find(addr);
 
 	return ksym && ksym->prog ?
 	       container_of(ksym, struct bpf_prog_aux, ksym)->prog :
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 8fef7b3cbd80..61b69eb08c4a 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2936,7 +2936,9 @@ static bool bpf_stack_walker(void *cookie, u64 ip, u64 sp, u64 bp)
 
 	if (!is_bpf_text_address(ip))
 		return !ctx->cnt;
+	rcu_read_lock();
 	prog = bpf_prog_ksym_find(ip);
+	rcu_read_unlock();
 	ctx->cnt++;
 	if (bpf_is_subprog(prog))
 		return true;
-- 
2.47.1