On Mon, 12 Oct 2026, [email protected] wrote: > Thank you for your contribution! Sashiko AI review found 2 potential issue(s) > to consider: > - [High] tracing: check_synth_field regression for __bitmask and stacktraces > - [High] tracing: arbitrary memory read via scalar to string synthetic field > mapping
Fixing now - v2 to follow shortly. Bear with. > -- > > commit 4813d717e995df13871068dd6fd996711ca8965d > Author: Lee Jones <[email protected]> > > tracing/histograms: Reject non-stacktrace fields for synthetic stacktrace > fields > > In check_synth_field(), when a synthetic event field is a stacktrace > and the histogram field is not a "long[" stacktrace array, validation falls > through to the generic size and signedness comparison. This allows any > 8-byte signed scalar histogram field to pass the fallback check and be > dereferenced as a kernel stacktrace pointer. This commit attempts to reject > these mismatches by enforcing that field->is_stack matches the "long[" type. > > > diff --git a/kernel/trace/trace_events_hist.c > > b/kernel/trace/trace_events_hist.c > > index 8af97fd4ee2d5..b09f5043e1543 100644 > > --- a/kernel/trace/trace_events_hist.c > > +++ b/kernel/trace/trace_events_hist.c > > @@ -3946,7 +3946,10 @@ static int check_synth_field(struct synth_event > > *event, > > && field->is_dynamic) > > return 0; > > > > - if (strstr(hist_field->type, "long[") && field->is_stack) > > + if (!!strstr(hist_field->type, "long[") != field->is_stack) > > + return -EINVAL; > > [Severity: High] > Does this heuristic falsely match the long[ substring in __data_loc unsigned > long[] from __bitmask and __cpumask fields? > > If is_stack == false, this logic seems to falsely reject valid mappings. > > If is_stack == true, this appears to bypass validation and allow a 32-bit > __data_loc integer to be passed as the field value. Could this 32-bit integer > then be cast to a pointer and dereferenced in > trace_events_synth.c:get_field_size() and trace_stack(), potentially causing > a kernel panic? > > > + > > + if (field->is_stack) > > return 0; > > > > if (strcmp(field->type, hist_field->type) != 0) { > > if (field->size != hist_field->size || > > (!field->is_string && field->is_signed != > > hist_field->is_signed)) > > return -EINVAL; > > } > > [Severity: High] > It looks like this fallback logic fails to reject a scalar-to-string mapping. > > When creating a dynamic string synthetic field, its size is set to sizeof(u64) > and is_string is true. Because field->size equals hist_field->size (8 bytes) > and !field->is_string short-circuits the type/signedness check, will an 8-byte > scalar successfully map to a dynamic string? > > If an attacker-controlled scalar is passed, can it be cast to a kernel pointer > in trace_events_synth.c:trace_string() and used with fetch_store_strlen() to > arbitrarily read kernel memory? > > -- > Sashiko AI review ยท > https://sashiko.dev/#/patchset/[email protected]?part=1 -- Lee Jones
