[PATCH v2 3/3] 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. When header_size (u8 from file) is 0, the expression
   *(buf + header_size - 1) reads one byte before the buffer.

2. 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().

3. 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, allowing arbitrary OOB reads.

Add bounds checks for all three cases: reject header_size of 0,
validate offsets in the block lookup loop, and validate the component
size read offset.

Signed-off-by: Sebastian Alba Vives <sebasjosue84@gmail.com>
---
 drivers/fpga/microchip-spi.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/fpga/microchip-spi.c b/drivers/fpga/microchip-spi.c
index 6134cea..7954dd0 100644
--- a/drivers/fpga/microchip-spi.c
+++ b/drivers/fpga/microchip-spi.c
@@ -116,7 +116,7 @@ static int mpf_ops_parse_header(struct fpga_manager *mgr,
 	}
 
 	header_size = *(buf + MPF_HEADER_SIZE_OFFSET);
-	if (header_size > count) {
+	if (!header_size || header_size > count) {
 		info->header_size = header_size;
 		return -EAGAIN;
 	}
@@ -139,6 +139,10 @@ 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)
+			return -EINVAL;
+
 		block_id = *(buf + block_id_offset);
 		block_start = get_unaligned_le32(buf + block_start_offset);
 
@@ -183,6 +187,10 @@ 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 +
+		    sizeof(u32) > count)
+			return -EINVAL;
+
 		component_size = get_unaligned_le32(buf +
 						    components_size_start +
 						    component_size_byte_num);
-- 
2.43.0