[PATCH bpf-next v2] bpf: Log error code on trampoline unlink failure

[xu.xin16]

From: xu xin <xu.xin16@xxxxxxxxxx>

Replace silent WARN_ON_ONCE with WARN_ONCE that prints the actual error
code from bpf_trampoline_unlink_prog(). This aids debugging of race
conditions during link teardown, while keeping the warning rate limited
to avoid log flooding.

This will be very helpful for speeding up trouble-shooting of some crash
UAF due to bpf_trampoline_unlink_prog failures.

No functional change intended.

Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
---
v1->v2:
1) clean the subject name by remove 'syscall' suggested by Leon Hwang
https://lore.kernel.org/all/20a444b2-aeed-4af8-ba76-e994e2c14087@xxxxxxxxx/
2) Add up the missed case in kernel/bpf/trampoline.c:bpf_shim_tramp_link_release()

kernel/bpf/syscall.c    | 9 ++++++---
 kernel/bpf/trampoline.c | 5 ++++-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6db306d23b47..2348dc33abf4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3626,10 +3626,13 @@ static void bpf_tracing_link_release(struct bpf_link *link)
 {
 	struct bpf_tracing_link *tr_link =
 		container_of(link, struct bpf_tracing_link, link.link);
+	int err;

-	WARN_ON_ONCE(bpf_trampoline_unlink_prog(&tr_link->link.node,
-						tr_link->trampoline,
-						tr_link->tgt_prog));
+	err = bpf_trampoline_unlink_prog(&tr_link->link.node,
+					tr_link->trampoline,
+					tr_link->tgt_prog);
+	if (err)
+		WARN_ONCE(err, "bpf_trampoline_unlink_prog returns error: %d\n", err);

 	bpf_trampoline_put(tr_link->trampoline);

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 1a721fc4bef5..dae3c2104ed4 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -997,12 +997,15 @@ static void bpf_shim_tramp_link_release(struct bpf_link *link)
 {
 	struct bpf_shim_tramp_link *shim_link =
 		container_of(link, struct bpf_shim_tramp_link, link.link);
+	int err;

 	/* paired with 'shim_link->trampoline = tr' in bpf_trampoline_link_cgroup_shim */
 	if (!shim_link->trampoline)
 		return;

-	WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link.node, shim_link->trampoline, NULL));
+	err = bpf_trampoline_unlink_prog(&shim_link->link.node, shim_link->trampoline, NULL);
+	if (err)
+		WARN_ONCE(err, "bpf_trampoline_unlink_prog returns error: %d\n", err);
 	bpf_trampoline_put(shim_link->trampoline);
 }

-- 
2.25.1