On 30/08/2025 02:28, Alexei Starovoitov wrote:
On Fri, Aug 29, 2025 at 11:50 AM Song Liu <song@xxxxxxxxxx> wrote:
On Fri, Aug 29, 2025 at 10:29 AM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
[...]
static long __bpf_get_stackid(struct bpf_map *map,
- struct perf_callchain_entry *trace, u64 flags)
+ struct perf_callchain_entry *trace, u64 flags, u32 max_depth)
{
struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
@@ -263,6 +263,8 @@ static long __bpf_get_stackid(struct bpf_map *map,
trace_nr = trace->nr - skip;
trace_len = trace_nr * sizeof(u64);
+ trace_nr = min(trace_nr, max_depth - skip);
+
The patch might have fixed this particular syzbot repro
with OOB in stackmap-with-buildid case,
but above two line looks wrong.
trace_len is computed before being capped by max_depth.
So non-buildid case below is using
memcpy(new_bucket->data, ips, trace_len);
so OOB is still there?
+1 for this observation.
We are calling __bpf_get_stackid() from two functions: bpf_get_stackid
and bpf_get_stackid_pe. The check against max_depth is only needed
from bpf_get_stackid_pe, so it is better to just check here.
Good point.
Nice catch, thanks !
I have got the following on top of patch 1/2. This makes more sense to
me.
PS: The following also includes some clean up in __bpf_get_stack.
I include those because it also uses stack_map_calculate_max_depth.
Does this look better?
yeah. It's certainly cleaner to avoid adding extra arg to
__bpf_get_stackid()
Are Song patches going to be applied then ? Or should I raise a new
revision
of the patch with Song's modifications with a Co-developped tag ?
Thanks for your guidance in advance,
Arnaud
