#syz test

--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -230,7 +230,7 @@ static long __bpf_get_stackid(struct bpf_map *map,
 	struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 	struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
 	u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
-	u32 hash, id, trace_nr, trace_len, i;
+	u32 hash, id, trace_nr, trace_len, i, max_depth;
 	bool user = flags & BPF_F_USER_STACK;
 	u64 *ips;
 	bool hash_matches;
@@ -241,6 +241,19 @@ static long __bpf_get_stackid(struct bpf_map *map,
 
 	trace_nr = trace->nr - skip;
 	trace_len = trace_nr * sizeof(u64);
+
+	/* Clamp the trace to max allowed depth */
+	if (stack_map_use_build_id(map))
+		max_depth = smap->map.value_size / sizeof(struct bpf_stack_build_id);
+	else
+		max_depth = smap->map.value_size / sizeof(u64);
+
+	if (trace_nr > max_depth)
+		trace_nr = max_depth;
+
+ 	ips = trace->ip + skip;
+
+
 	ips = trace->ip + skip;
 	hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
 	id = hash & (smap->n_buckets - 1);
--

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com
Tested-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com

Tested on:

commit:         cd7c97f4 Merge branch 'bpf-show-precise-rejected-funct..
git tree:       bpf-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15fe44a2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=934611ae034ab218
dashboard link: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11bbb4a2580000

Note: testing is done by a robot and is best-effort only.