[PATCH] drm/radeon: Bound GPIO I2C table entry count from VBIOS

[Andrey Misiurov <amisiurov@cloudlinux.com>]

radeon_atombios_i2c_init() derives the number of GPIO I2C entries from
the size field of the VBIOS GPIO_I2C_Info table and stores a bus for
every valid entry in rdev->i2c_bus[i], which has RADEON_MAX_I2C_BUS
(16) slots.  A table that claims more than 16 entries makes it write
past the end of the array into the rest of struct radeon_device.  A
size smaller than the common header wraps the subtraction and the loop
walks far past the table.  radeon_lookup_i2c_gpio() uses the same
calculation.

Reject undersized tables and cap the entry count at
RADEON_MAX_I2C_BUS.

Fixes: f376b94fbc0a ("drm/radeon/kms: unify i2c handling")
Cc: stable@vger.kernel.org
Signed-off-by: Andrey Misiurov <amisiurov@cloudlinux.com>
---
Found by code inspection.  Not reproduced at runtime; it needs a VBIOS
with a malformed GPIO_I2C_Info table.

 drivers/gpu/drm/radeon/radeon_atombios.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_atombios.c b/drivers/gpu/drm/radeon/radeon_atombios.c
index 3dd9724..c4e1272 100644
--- a/drivers/gpu/drm/radeon/radeon_atombios.c
+++ b/drivers/gpu/drm/radeon/radeon_atombios.c
@@ -125,6 +125,22 @@ static struct radeon_i2c_bus_rec radeon_get_bus_rec_for_i2c_gpio(ATOM_GPIO_I2C_A
 	return i2c;
 }
 
+/*
+ * The VBIOS table size is not checked against the image; cap the
+ * entry count to RADEON_MAX_I2C_BUS, the size of rdev->i2c_bus[].
+ */
+static int radeon_atombios_gpio_i2c_num_entries(uint16_t size)
+{
+	u32 bytes;
+
+	if (size < sizeof(ATOM_COMMON_TABLE_HEADER))
+		return 0;
+
+	bytes = size - sizeof(ATOM_COMMON_TABLE_HEADER);
+	return min_t(u32, bytes / sizeof(ATOM_GPIO_I2C_ASSIGMENT),
+		     RADEON_MAX_I2C_BUS);
+}
+
 static struct radeon_i2c_bus_rec radeon_lookup_i2c_gpio(struct radeon_device *rdev,
 							       uint8_t id)
 {
@@ -142,8 +158,7 @@ static struct radeon_i2c_bus_rec radeon_lookup_i2c_gpio(struct radeon_device *rd
 	if (atom_parse_data_header(ctx, index, &size, NULL, NULL, &data_offset)) {
 		i2c_info = (struct _ATOM_GPIO_I2C_INFO *)(ctx->bios + data_offset);
 
-		num_indices = (size - sizeof(ATOM_COMMON_TABLE_HEADER)) /
-			sizeof(ATOM_GPIO_I2C_ASSIGMENT);
+		num_indices = radeon_atombios_gpio_i2c_num_entries(size);
 
 		gpio = &i2c_info->asGPIO_Info[0];
 		for (i = 0; i < num_indices; i++) {
@@ -176,8 +191,7 @@ void radeon_atombios_i2c_init(struct radeon_device *rdev)
 	if (atom_parse_data_header(ctx, index, &size, NULL, NULL, &data_offset)) {
 		i2c_info = (struct _ATOM_GPIO_I2C_INFO *)(ctx->bios + data_offset);
 
-		num_indices = (size - sizeof(ATOM_COMMON_TABLE_HEADER)) /
-			sizeof(ATOM_GPIO_I2C_ASSIGMENT);
+		num_indices = radeon_atombios_gpio_i2c_num_entries(size);
 
 		gpio = &i2c_info->asGPIO_Info[0];
 		for (i = 0; i < num_indices; i++) {
-- 
2.43.7