[PATCH v3] fpga: microchip-spi: add bounds checks in mpf_ops_parse_header()

[Sebastian Alba Vives <sebasjosue84@gmail.com>]

From: Sebastian Josue Alba Vives <sebasjosue84@gmail.com>

mpf_ops_parse_header() reads several fields from the bitstream file
and uses them as offsets and sizes without validating them against the
buffer size, leading to multiple out-of-bounds read vulnerabilities:

1. There is no check that count is large enough to read header_size
   at MPF_HEADER_SIZE_OFFSET (24). Add a minimum count check.

2. When header_size (u8 from file) is 0, the expression
   *(buf + header_size - 1) reads one byte before the buffer.
   Return -EINVAL since retrying with a larger buffer cannot fix
   a zero header_size.

3. In the block lookup loop, block_id_offset and block_start_offset
   advance by MPF_LOOKUP_TABLE_RECORD_SIZE (9) each iteration with
   blocks_num (u8) controlling the count. With a small buffer, these
   offsets exceed count, causing OOB reads via get_unaligned_le32().
   Return -EAGAIN with updated header_size so the retry mechanism
   can request a larger buffer.

4. components_num is read from MPF_DATA_SIZE_OFFSET without checking
   that the offset is within bounds. Add a bounds check.

5. components_size_start (from file) and component_size_byte_num
   (derived from components_num, u16 from file) are used as offsets
   into buf without validation. On 32-bit architectures, their sum
   could overflow, bypassing the bounds check. Add an overflow check
   before the bounds comparison.

Add bounds checks for all five cases.

Fixes: 5f8d4a9008307 ("fpga: microchip-spi: add Microchip MPF FPGA manager")
Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Alba Vives <sebasjosue84@gmail.com>
---
Changes in v3:
  - Add overflow check for 32-bit architectures in component size loop
  - Add bounds check for MPF_DATA_SIZE_OFFSET read
  - Update info->header_size before returning -EAGAIN in block loop
    so the retry mechanism can request a larger buffer

Changes in v2:
  - Return -EINVAL instead of -EAGAIN for header_size == 0
  - Return -EAGAIN instead of -EINVAL in block lookup loop
  - Add count check before reading at MPF_HEADER_SIZE_OFFSET
 drivers/fpga/microchip-spi.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/fpga/microchip-spi.c b/drivers/fpga/microchip-spi.c
index 6134cea..10be986 100644
--- a/drivers/fpga/microchip-spi.c
+++ b/drivers/fpga/microchip-spi.c
@@ -115,7 +115,13 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
 		return -EINVAL;
 	}
 
+	if (count < MPF_HEADER_SIZE_OFFSET + 1)
+		return -EINVAL;
+
 	header_size = *(buf + MPF_HEADER_SIZE_OFFSET);
+	if (!header_size)
+		return -EINVAL;
+
 	if (header_size > count) {
 		info->header_size = header_size;
 		return -EAGAIN;
@@ -139,6 +145,12 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
 	bitstream_start = 0;
 
 	while (blocks_num--) {
+		if (block_id_offset >= count ||
+		    block_start_offset + sizeof(u32) > count) {
+			info->header_size = block_start_offset + sizeof(u32);
+			return -EAGAIN;
+		}
+
 		block_id = *(buf + block_id_offset);
 		block_start = get_unaligned_le32(buf + block_start_offset);
 
@@ -175,6 +187,9 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
 	 * to each other. Image header should be extended by now up to where
 	 * actual bitstream starts, so no need for overflow check anymore.
 	 */
+	if (MPF_DATA_SIZE_OFFSET + sizeof(u16) > count)
+		return -EINVAL;
+
 	components_num = get_unaligned_le16(buf + MPF_DATA_SIZE_OFFSET);
 
 	for (i = 0; i < components_num; i++) {
@@ -183,6 +198,11 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
 		component_size_byte_off =
 			(i * MPF_BITS_PER_COMPONENT_SIZE) % BITS_PER_BYTE;
 
+		if (components_size_start + component_size_byte_num < components_size_start ||
+		    components_size_start + component_size_byte_num +
+		    sizeof(u32) > count)
+			return -EINVAL;
+
 		component_size = get_unaligned_le32(buf +
 						    components_size_start +
 						    component_size_byte_num);
-- 
2.43.0