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Subjectre: net/mlx5: Refactor tc flow attributes structure

static analysis with Coverity has found a null pointer dereference issue
with the following commit:

commit c620b772152b8274031083bdb2e11c963e596c5c
Author: Ariel Levkovich <>
Date: Thu Apr 30 05:54:08 2020 +0300

net/mlx5: Refactor tc flow attributes structure

The analysis is as follows:

1240 slow_attr = mlx5_alloc_flow_attr(MLX5_FLOW_NAMESPACE_FDB);

1. Condition !slow_attr, taking true branch.
2. var_compare_op: Comparing slow_attr to null implies that
slow_attr might be null.

1241 if (!slow_attr)
1242 mlx5_core_warn(flow->priv->mdev, "Unable to
unoffload slow path rule\n");
1244 memcpy(slow_attr, flow->attr, ESW_FLOW_ATTR_SZ);

Dereference after null check (FORWARD_NULL)
3. var_deref_op: Dereferencing null pointer slow_attr.

1245 slow_attr->action = MLX5_FLOW_CONTEXT_ACTION_FWD_DEST;
1246 slow_attr->esw_attr->split_count = 0;
1247 slow_attr->flags |= MLX5_ESW_ATTR_FLAG_SLOW_PATH;
1248 mlx5e_tc_unoffload_fdb_rules(esw, flow, slow_attr);
1249 flow_flag_clear(flow, SLOW);
1250 kfree(slow_attr);

there is a !slow_attr check but if it slow_attr is null the code then
dereferences it multiple times afterwards.


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