[PATCH] fastboot: Fix blk_dwrite error checking

[PATCH] fastboot: Fix blk_dwrite error checking

[Francois Berder]

blk_dwrite() returns the number of blocks written.
The code was only checking if the return value was different
than 0. Hence, partial writes were considered successful.
Fix blk_dwrite error handling by checking that all blocks
are written.

Signed-off-by: Francois Berder <fberder@outlook.fr>
---
 drivers/fastboot/fb_mmc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/fastboot/fb_mmc.c b/drivers/fastboot/fb_mmc.c
index 11d9c8e8460..9bc782ccd02 100644
--- a/drivers/fastboot/fb_mmc.c
+++ b/drivers/fastboot/fb_mmc.c
@@ -263,7 +263,7 @@ static int fb_mmc_update_zimage(struct blk_desc *dev_desc,
 	/* Write new kernel size to boot image header */
 	hdr->kernel_size = download_bytes;
 	res = blk_dwrite(dev_desc, info.start, hdr_sectors, (void *)hdr);
-	if (res == 0) {
+	if (res != hdr_sectors) {
 		pr_err("cannot writeback boot image header\n");
 		fastboot_fail("cannot write back boot image header", response);
 		return -1;
@@ -275,7 +275,7 @@ static int fb_mmc_update_zimage(struct blk_desc *dev_desc,
 				      sectors_per_page;
 	res = blk_dwrite(dev_desc, kernel_sector_start, kernel_sectors,
 			 download_buffer);
-	if (res == 0) {
+	if (res != kernel_sectors) {
 		pr_err("cannot write new kernel\n");
 		fastboot_fail("cannot write new kernel", response);
 		return -1;
@@ -287,7 +287,7 @@ static int fb_mmc_update_zimage(struct blk_desc *dev_desc,
 					     sectors_per_page;
 	res = blk_dwrite(dev_desc, ramdisk_sector_start, ramdisk_sectors,
 			 ramdisk_buffer);
-	if (res == 0) {
+	if (res != ramdisk_sectors) {
 		pr_err("cannot write back original ramdisk\n");
 		fastboot_fail("cannot write back original ramdisk", response);
 		return -1;
-- 
2.43.0

Re: [PATCH] fastboot: Fix blk_dwrite error checking

[Mattijs Korpershoek]

Hi Francois,

Thank you for the patch.

On Sun, May 24, 2026 at 21:25, Francois Berder <fberder@outlook.fr> wrote:

> blk_dwrite() returns the number of blocks written.
> The code was only checking if the return value was different
> than 0. Hence, partial writes were considered successful.
> Fix blk_dwrite error handling by checking that all blocks
> are written.
>
> Signed-off-by: Francois Berder <fberder@outlook.fr>

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>

> ---