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 v6: https://lore.kernel.org/all/20250903135348.97884-1-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 | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 9f3ae426ddc3..29e05c9ff1bd 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -369,6 +369,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, { struct perf_event *event = ctx->event; struct perf_callchain_entry *trace; + u32 elem_size, max_depth; bool kernel, user; __u64 nr_kernel; int ret; @@ -390,11 +391,15 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, return -EFAULT; nr_kernel = count_kernel_ip(trace); + elem_size = stack_map_data_size(map); if (kernel) { __u64 nr = trace->nr; trace->nr = nr_kernel; + max_depth = + stack_map_calculate_max_depth(map->value_size, elem_size, flags); + trace->nr = min_t(u32, nr_kernel, max_depth); ret = __bpf_get_stackid(map, trace, flags); /* restore nr */ @@ -407,6 +412,9 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, return -EFAULT; flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip; + max_depth = + stack_map_calculate_max_depth(map->value_size, elem_size, flags); + trace->nr = min_t(u32, trace->nr, max_depth); ret = __bpf_get_stackid(map, trace, flags); } return ret; -- 2.47.3
