From: Arnaud Lecomte 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. Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com 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 Acked-by: Yonghong Song --- Changes in v2: - Fixed max_depth names across get stack id Changes in v4: - Removed unnecessary empty line in __bpf_get_stackid Changes in v6: - Added back trace_len computation in __bpf_get_stackid Changes in v7: - Removed usefull trace->nr assignation in bpf_get_stackid_pe - Added restoration of trace->nr for both kernel and user traces in bpf_get_stackid_pe Link to v7: https://lore.kernel.org/all/20250903234325.30212-1-contact@arnaud-lcm.com/ --- kernel/bpf/stackmap.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 9f3ae426ddc3..9b57b8307565 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; @@ -390,15 +391,16 @@ 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); + __u64 nr = trace->nr; /* save original */ 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 */ - trace->nr = nr; } else { /* user */ u64 skip = flags & BPF_F_SKIP_FIELD_MASK; @@ -407,8 +409,15 @@ 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); } + + /* restore nr */ + trace->nr = nr; + return ret; } -- 2.47.3