[PATCH v4 3/3] fpga: microchip-spi: fix OOB read in mpf_ops_parse_header()

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

mpf_ops_parse_header() reads header_size at MPF_HEADER_SIZE_OFFSET (24)
without first checking that count is large enough, leading to an
out-of-bounds read if the buffer is smaller than 25 bytes.

Additionally, when header_size is zero, the expression
*(buf + header_size - 1) reads one byte before the buffer start.
Since a zero header_size cannot be resolved by providing a larger
buffer, return -EINVAL instead of falling through.

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 v4:
  - Reduce to two minimal fixes only: minimum count check before
    reading header_size, and -EINVAL for zero header_size.
    Drop redundant block loop checks — the pre-loop bounds extension
    already ensures all block offsets are within count.
    Suggested by Xu Yilun.
Changes in v3:
  - Add overflow check for 32-bit in component size loop.
Changes in v2:
  - Return -EINVAL for header_size == 0, -EAGAIN in block loop,
    add count check before MPF_HEADER_SIZE_OFFSET read.
---
 drivers/fpga/microchip-spi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/fpga/microchip-spi.c b/drivers/fpga/microchip-spi.c
index 6134cea..dca1a5d 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;
-- 
2.43.0