FAILED: patch "[PATCH] tracing/histograms: Reject non-stacktrace fields for" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x a244c241593b5b38a08f0df2cb43c26574efbdcb
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026102126-gallantly-unknotted-4bc4@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a244c241593b5b38a08f0df2cb43c26574efbdcb Mon Sep 17 00:00:00 2001
From: Lee Jones <[email protected]>
Date: Tue, 13 Oct 2026 11:24:48 +0000
Subject: [PATCH] tracing/histograms: Reject non-stacktrace fields for
synthetic stacktrace fields

In check_synth_field(), when a synthetic event field is a stacktrace (field->is_stack) and the histogram field is not a "long[" stacktrace array, validation falls through to the generic size and signedness comparison.

Because parse_synth_field() sets a stacktrace field's type to "__data_loc unsigned long[]", its size is sizeof(u64) and synth_field_signed() marks it as signed. Consequently, any 8-byte signed scalar histogram field passes the fallback check, and its scalar value is subsequently dereferenced as a kernel stacktrace pointer in get_field_size() and trace_stack().

Furthermore, checking strstr(hist_field->type, "long[") is insufficient because tracepoint fields defined with __bitmask() or __rel_bitmask() also have type "__data_loc unsigned long[]" or "__rel_loc unsigned long[]", whilst create_hist_field() treats them as 4-byte scalar values without HIST_FIELD_FL_STACKTRACE.

Propagate HIST_FIELD_FL_STACKTRACE to variable references and field variables (whilst excluding variable aliases from per-element stacktrace capture), and reject any mismatch between HIST_FIELD_FL_STACKTRACE and field->is_stack in check_synth_field().

index 571a57e0f369..dcb5d7321095 100644
@@ -2121,7 +2121,8 @@ static int init_var_ref(struct hist_field *ref_field,
 	ref_field->size = var_field->size;
 	ref_field->is_signed = var_field->is_signed;
 	ref_field->flags |= var_field->flags &
-		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
+		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS |
+		 HIST_FIELD_FL_STACKTRACE);
 
 	if (system) {
 		ref_field->system = kstrdup(system, GFP_KERNEL);

@@ -3318,6 +3319,7 @@ static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
 		ret = PTR_ERR(var);
 		goto err;
 	}
+	var->flags |= val->flags & HIST_FIELD_FL_STACKTRACE;
 
 	field_var = kzalloc_obj(struct field_var);
 	if (!field_var) {

@@ -3946,7 +3948,10 @@ static int check_synth_field(struct synth_event *event,
 	    && field->is_dynamic)
 		return 0;
 
-	if (strstr(hist_field->type, "long[") && field->is_stack)
+	if (!!(hist_field->flags & HIST_FIELD_FL_STACKTRACE) != field->is_stack)
+		return -EINVAL;
+
+	if (field->is_stack)
 		return 0;
 
 	if (strcmp(field->type, hist_field->type) != 0) {

@@ -4487,7 +4492,8 @@ static int create_var_field(struct hist_trigger_data *hist_data,
 	if (!ret && hist_data->fields[val_idx]->flags & HIST_FIELD_FL_EXECNAME)
 		update_var_execname(hist_data->fields[val_idx]);
 
-	if (!ret && hist_data->fields[val_idx]->flags &
+	if (!ret && !(hist_data->fields[val_idx]->flags & HIST_FIELD_FL_ALIAS) &&
+	    hist_data->fields[val_idx]->flags &
 	    (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE))
 		hist_data->fields[val_idx]->var_str_idx = hist_data->n_var_str++;
 

@@ -5228,7 +5234,8 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 		if (hist_field->flags & HIST_FIELD_FL_VAR) {
 			var_idx = hist_field->var.idx;
 
-			if (hist_field->flags &
+			if (!(hist_field->flags & HIST_FIELD_FL_ALIAS) &&
+			    hist_field->flags &
 			    (HIST_FIELD_FL_STRING | HIST_FIELD_FL_STACKTRACE)) {
 				unsigned int str_start, var_str_idx, idx;
 				char *str, *val_str;