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R. Silva" , linux-kernel@vger.kernel.org (open list:TRACING), linux-hardening@vger.kernel.org (open list:KERNEL HARDENING (not covered by other areas):Keyword:\b__counted_by(_le|_be|_ptr)?\b) Subject: [PATCH] trace: turn hist_elt_data field_var_str into a flexible array Date: Fri, 22 May 2026 14:44:07 -0700 Message-ID: <20260522214407.18120-1-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. Assisted-by: Claude:Opus-4.7 Signed-off-by: Rosen Penev --- kernel/trace/trace_events_hist.c | 31 +++++++++++-------------------- 1 file changed, 11 insertions(+), 20 deletions(-) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_h= ist.c index a64c76f6905f..1fd0899c606c 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -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); }; =20 struct snapshot_context { @@ -1629,8 +1629,6 @@ static void hist_elt_data_free(struct hist_elt_data *= elt_data) for (i =3D 0; i < elt_data->n_field_var_str; i++) kfree(elt_data->field_var_str[i]); =20 - 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 traci= ng_map_elt *elt) struct hist_field *hist_field; unsigned int i, n_str; =20 - elt_data =3D kzalloc_obj(*elt_data); + BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1)); + + n_str =3D 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 =3D kzalloc_flex(*elt_data, field_var_str, n_str); if (!elt_data) return -ENOMEM; =20 + elt_data->n_field_var_str =3D n_str; + for_each_hist_field(i, hist_data) { hist_field =3D hist_data->fields[i]; =20 @@ -1667,24 +1674,8 @@ static int hist_trigger_elt_data_alloc(struct tracin= g_map_elt *elt) } } =20 - n_str =3D 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 =3D STR_VAR_LEN_MAX; =20 - elt_data->field_var_str =3D 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 =3D n_str; - for (i =3D 0; i < n_str; i++) { elt_data->field_var_str[i] =3D kzalloc(size, GFP_KERNEL); if (!elt_data->field_var_str[i]) { --=20 2.54.0