Syzkaller reported a KASAN slab-out-of-bounds write in __bpf_get_stackid() when copying stack trace data. The issue occurs when the perf trace contains more stack entries than the stack map bucket can hold, leading to an out-of-bounds write in the bucket's data array. For build_id mode, we use sizeof(struct bpf_stack_build_id) to determine capacity, and for normal mode we use sizeof(u64). Reported-by: syzbot+c9b724fbb41cf2538b7b@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b Tested-by: syzbot+c9b724fbb41cf2538b7b@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Arnaud Lecomte <contact@xxxxxxxxxxxxxx> --- Changes in v2: - Use utilty stack_map_data_size to compute map stack map size --- kernel/bpf/stackmap.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 3615c06b7dfa..6f225d477f07 100644 --- 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 +241,12 @@ 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 */ + max_depth = smap->map.value_size / stack_map_data_size(map); + if (trace_nr > max_depth) + trace_nr = max_depth; + ips = trace->ip + skip; hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); id = hash & (smap->n_buckets - 1); -- 2.43.0
