linux-kernel - [PATCH bpf-next v7 2/3] bpf: clean-up bounds checking in __bpf_get

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Message-Id: <20250903234052.29678-1-contact@arnaud-lcm.com>
Date: Thu,  4 Sep 2025 01:40:52 +0200
From: Arnaud Lecomte <contact@...aud-lcm.com>
To: alexei.starovoitov@...il.com,
	yonghong.song@...ux.dev,
	song@...nel.org
Cc: andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
	daniel@...earbox.net,
	eddyz87@...il.com,
	haoluo@...gle.com,
	john.fastabend@...il.com,
	jolsa@...nel.org,
	kpsingh@...nel.org,
	linux-kernel@...r.kernel.org,
	martin.lau@...ux.dev,
	sdf@...ichev.me,
	syzbot+c9b724fbb41cf2538b7b@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com,
	Arnaud Lecomte <contact@...aud-lcm.com>
Subject: [PATCH bpf-next v7 2/3] bpf: clean-up bounds checking in
 __bpf_get_stack

Clean-up bounds checking for trace->nr in
__bpf_get_stack by limiting it only to
max_depth.

Signed-off-by: Arnaud Lecomte <contact@...aud-lcm.com>
Cc: Song Lui <song@...nel.org>
---
 kernel/bpf/stackmap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index ed707bc07173..9f3ae426ddc3 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -462,13 +462,15 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 	if (may_fault)
 		rcu_read_lock(); /* need RCU for perf's callchain below */
 
-	if (trace_in)
+	if (trace_in) {
 		trace = trace_in;
-	else if (kernel && task)
+		trace->nr = min_t(u32, trace->nr, max_depth);
+	} else if (kernel && task) {
 		trace = get_callchain_entry_for_task(task, max_depth);
-	else
+	} else {
 		trace = get_perf_callchain(regs, 0, kernel, user, max_depth,
 					   crosstask, false);
+	}
 
 	if (unlikely(!trace) || trace->nr < skip) {
 		if (may_fault)
@@ -477,7 +479,6 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
 	}
 
 	trace_nr = trace->nr - skip;
-	trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
 	copy_len = trace_nr * elem_size;
 
 	ips = trace->ip + skip;
-- 
2.47.3