[PATCH v4 1/4] PCI: of: avoid allocations in of_pci_prop_compatible()

[Alex Elder <elder@riscstar.com>]

Three compatible strings are formatted in of_pci_prop_compatible().
Their sizes are known in advance, and the largest is 16 bytes.

Rather than dynamically allocating the space for those strings, just
set aside a buffer on the stack large enough to hold all three.

This avoids a problem that Sashiko pointed out, where an allocation
failure would cause subsequent crash because strlen() is called
unconditionally in of_changeset_add_prop_string_array().

Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/sashiko-reviews/a647bd56-7dc8-4fec-9d96-834622054cdf@riscstar.com
Signed-off-by: Alex Elder <elder@riscstar.com>
---
v4: - Added this fix to the beginning of the series

 drivers/pci/of_property.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/drivers/pci/of_property.c b/drivers/pci/of_property.c
index 75a358f73e694..a0632f932b5c6 100644
--- a/drivers/pci/of_property.c
+++ b/drivers/pci/of_property.c
@@ -324,27 +324,36 @@ static int of_pci_prop_intr_map(struct pci_dev *pdev, struct of_changeset *ocs,
 	return ret;
 }
 
+/* The three compatible property strings have max sizes 12+1, 15+1, and 13+1 */
+#define PROP_SIZE	16	/* Max size of each compatible string */
 static int of_pci_prop_compatible(struct pci_dev *pdev,
 				  struct of_changeset *ocs,
 				  struct device_node *np)
 {
 	const char *compat_strs[PROP_COMPAT_NUM] = { 0 };
+	char buf[PROP_COMPAT_NUM * PROP_SIZE] = { };
+	char bufp = buf;
 	int i, ret;
 
-	compat_strs[PROP_COMPAT_PCI_VVVV_DDDD] =
-		kasprintf(GFP_KERNEL, "pci%x,%x", pdev->vendor, pdev->device);
-	compat_strs[PROP_COMPAT_PCICLASS_CCSSPP] =
-		kasprintf(GFP_KERNEL, "pciclass,%06x", pdev->class);
-	compat_strs[PROP_COMPAT_PCICLASS_CCSS] =
-		kasprintf(GFP_KERNEL, "pciclass,%04x", pdev->class >> 8);
+	ret = snprintf(bufp, PROP_SIZE, "pci%x,%x", pdev->vendor, pdev->device);
+	if (ret >= PROP_SIZE)
+		return -EINVAL;
+	compat_strs[PROP_COMPAT_PCI_VVVV_DDDD] = bufp;
+	bufp += ret + 1;
 
-	ret = of_changeset_add_prop_string_array(ocs, np, "compatible",
-						 compat_strs, PROP_COMPAT_NUM);
-	for (i = 0; i < PROP_COMPAT_NUM; i++)
-		kfree(compat_strs[i]);
+	ret = snprintf(bufp, PROP_SIZE, "pciclass,%06x", pdev->class);
+	if (ret >= PROP_SIZE)
+		return -EINVAL;
+	compat_strs[PROP_COMPAT_PCICLASS_CCSSPP] = bufp;
+	bufp += ret + 1;
 
-	return ret;
+	ret = snprintf(bufp, PROP_SIZE, "pciclass,%04x", pdev->class >> 8);
+	compat_strs[PROP_COMPAT_PCICLASS_CCSS] = bufp;
+
+	return of_changeset_add_prop_string_array(ocs, np, "compatible",
+						  compat_strs, PROP_COMPAT_NUM);
 }
+#undef PROP_SIZE
 
 int of_pci_add_properties(struct pci_dev *pdev, struct of_changeset *ocs,
 			  struct device_node *np)
-- 
2.53.0