[PATCH] mtd: afs: validate v2 image info bounds

[PATCH] mtd: afs: validate v2 image info bounds

[Pengpeng Hou]

The AFS v2 parser uses footer[8] to locate the image information block
inside the current erase block, then uses the image information
region_count to walk entries from a fixed local array. The footer offset
and region count come from flash contents and were not checked against the
erase block or the local image-info array before use.

Reject v2 entries whose image information offset would underflow the erase
block calculation, and reject region counts that cannot fit in the local
image-info array before walking region entries.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 drivers/mtd/parsers/afs.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/mtd/parsers/afs.c b/drivers/mtd/parsers/afs.c
index 26116694c821..7ab3d50f565e 100644
--- a/drivers/mtd/parsers/afs.c
+++ b/drivers/mtd/parsers/afs.c
@@ -235,6 +235,9 @@ static int afs_parse_v2_partition(struct mtd_info *mtd,
 	pr_debug("Parsing v2 partition @%08x-%08x\n",
 		 off, off + mtd->erasesize);
 
+	if (mtd->erasesize < sizeof(footer))
+		return -EINVAL;
+
 	/* First read the footer */
 	ptr = off + mtd->erasesize - sizeof(footer);
 	ret = mtd_read(mtd, ptr, sizeof(footer), &sz, (u_char *)footer);
@@ -245,6 +248,8 @@ static int afs_parse_v2_partition(struct mtd_info *mtd,
 	}
 	name = (char *) &footer[0];
 	version = footer[9];
+	if (footer[8] > mtd->erasesize - sizeof(footer))
+		return -EINVAL;
 	ptr = off + mtd->erasesize - sizeof(footer) - footer[8];
 
 	pr_debug("found image \"%s\", version %08x, info @%08x\n",
@@ -278,6 +283,8 @@ static int afs_parse_v2_partition(struct mtd_info *mtd,
 	entrypoint = imginfo[pad];
 	attributes = imginfo[pad+1];
 	region_count = imginfo[pad+2];
+	if (region_count > (ARRAY_SIZE(imginfo) - pad - 3) / 4)
+		return -EINVAL;
 	block_start = imginfo[20];
 	block_end = imginfo[21];
 
-- 
2.43.0

Re: [PATCH] mtd: afs: validate v2 image info bounds

[Miquel Raynal]

On 06/07/2026 at 17:40:59 +08, Pengpeng Hou <pengpeng@iscas.ac.cn> wrote:

> The AFS v2 parser uses footer[8] to locate the image information block
> inside the current erase block, then uses the image information
> region_count to walk entries from a fixed local array. The footer offset
> and region count come from flash contents and were not checked against the
> erase block or the local image-info array before use.
>
> Reject v2 entries whose image information offset would underflow the erase
> block calculation, and reject region counts that cannot fit in the local
> image-info array before walking region entries.
>
> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>

I'll let you guess what is missing in this contribution?

Thanks,
Miquèl