re: misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge

From: Colin Ian King
Date: Tue May 18 2021 - 14:32:14 EST


Static analysis on linux-next with Coverity has detected an issue in
drivers/misc/cardreader/alcor_pci.c in function
alcor_pci_init_check_aspm with the following commit:

commit 3ce3e45cc333da707d4d6eb433574b990bcc26f5
Author: Tong Zhang <ztong0001@xxxxxxxxx>
Date: Thu May 13 00:07:33 2021 -0400

misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge

The analysis is as follows:

135 static void alcor_pci_init_check_aspm(struct alcor_pci_priv *priv)
136 {
137 struct pci_dev *pci;
138 int where;
139 u32 val32;
141 priv->pdev_cap_off = alcor_pci_find_cap_offset(priv,
142 /*
143 * A device might be attached to root complex directly and
144 * priv->parent_pdev will be NULL. In this case we don't
check its
145 * capability and disable ASPM completely.
146 */

1. Condition !priv->parent_pdev, taking true branch.
2. var_compare_op: Comparing priv->parent_pdev to null implies that
priv->parent_pdev might be null.

147 if (!priv->parent_pdev)

Dereference after null check (FORWARD_NULL)
3. var_deref_model: Passing null pointer priv->parent_pdev to
alcor_pci_find_cap_offset, which dereferences it.

148 priv->parent_cap_off = alcor_pci_find_cap_offset(priv,

When !priv->parent_pdev is true, then priv->parent_pdev is NULL and
hence the call to alcor_pci_find_cap_offset() is dereferencing a null
pointer in the priv->parent_pdev argument.

I suspect the logic in the if statement is inverted, the ! should be
removed. This seems too trivial to be wrong. Maybe I'm missing something