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tracing: Turn hist_elt_data field_var_str into a flexible array

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The field_var_str array was allocated separately via kcalloc() with its
length already known at elt_data allocation time.  Convert it to a
flexible array member and fold the two allocations into a single
kzalloc_flex(), reordering hist_trigger_elt_data_alloc() so n_str is
computed and bounds-checked before the struct allocation.

hist_elt_data is only reached through tracing_map_elt::private_data
(a void *), never embedded, so adding a FAM imposes no tail-position
constraint on any enclosing struct.

Added __counted_by for extra runtime analysis.

Link: https://patch.msgid.link/20260522214407.18120-1-rosenp@gmail.com
Assisted-by: Claude:Opus-4.7
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Rosen Penev 2026-05-22 14:44:07 -07:00 committed by Steven Rostedt
parent 292c8197e3
commit bfda3b9424
1 changed files with 11 additions and 20 deletions
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31
kernel/trace/trace_events_hist.c
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@ -683,8 +683,8 @@ struct track_data {
struct hist_elt_data {
char *comm;
u64 *var_ref_vals;
char **field_var_str;
int n_field_var_str;
char *field_var_str[] __counted_by(n_field_var_str);
};
struct snapshot_context {
@ -1629,8 +1629,6 @@ static void hist_elt_data_free(struct hist_elt_data *elt_data)
for (i = 0; i < elt_data->n_field_var_str; i++)
kfree(elt_data->field_var_str[i]);
kfree(elt_data->field_var_str);
kfree(elt_data->comm);
kfree(elt_data);
}
@ -1650,10 +1648,19 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
struct hist_field *hist_field;
unsigned int i, n_str;
elt_data = kzalloc_obj(*elt_data);
BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1));
n_str = hist_data->n_field_var_str + hist_data->n_save_var_str +
hist_data->n_var_str;
if (n_str > SYNTH_FIELDS_MAX)
return -EINVAL;
elt_data = kzalloc_flex(*elt_data, field_var_str, n_str);
if (!elt_data)
return -ENOMEM;
elt_data->n_field_var_str = n_str;
for_each_hist_field(i, hist_data) {
hist_field = hist_data->fields[i];
@ -1667,24 +1674,8 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
}
}
n_str = hist_data->n_field_var_str + hist_data->n_save_var_str +
hist_data->n_var_str;
if (n_str > SYNTH_FIELDS_MAX) {
hist_elt_data_free(elt_data);
return -EINVAL;
}
BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1));
size = STR_VAR_LEN_MAX;
elt_data->field_var_str = kcalloc(n_str, sizeof(char *), GFP_KERNEL);
if (!elt_data->field_var_str) {
hist_elt_data_free(elt_data);
return -EINVAL;
}
elt_data->n_field_var_str = n_str;
for (i = 0; i < n_str; i++) {
elt_data->field_var_str[i] = kzalloc(size, GFP_KERNEL);
if (!elt_data->field_var_str[i]) {