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. Changes in v2: - Fixed max_depth names across get stack id Changes in v4: - Removed unnecessary empty line in __bpf_get_stackid Changs in v6: - Added back trace_len computation in __bpf_get_stackid Link to v5: https://lore.kernel.org/all/20250826212229.143230-1-contact@xxxxxxxxxxxxxx/ Reported-by: syzbot+c9b724fbb41cf2538b7b@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b Fixes: ee2a098851bf ("bpf: Adjust BPF stack helper functions to accommodate skip > 0") Signed-off-by: Arnaud Lecomte <contact@xxxxxxxxxxxxxx> Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx> --- kernel/bpf/stackmap.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 1ebc525b7c2f..8b2dcb8a6dc3 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -251,8 +251,9 @@ 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 hash, id, trace_nr, trace_len, i, max_depth; u32 skip = flags & BPF_F_SKIP_FIELD_MASK; - u32 hash, id, trace_nr, trace_len, i; + u32 elem_size = stack_map_data_size(map); bool user = flags & BPF_F_USER_STACK; u64 *ips; bool hash_matches; @@ -261,8 +262,12 @@ static long __bpf_get_stackid(struct bpf_map *map, /* skipping more than usable stack trace */ return -EFAULT; + max_depth = + stack_map_calculate_max_depth(map->value_size, elem_size, flags); trace_nr = trace->nr - skip; + trace_nr = min_t(u32, trace_nr, max_depth - skip); trace_len = trace_nr * sizeof(u64); + ips = trace->ip + skip; hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); id = hash & (smap->n_buckets - 1); -- 2.47.3
