[PATCH] mtd: mtdpart: validate partition bounds in mtd_add_partition()

[Deepanshu Kartikey <kartikey406@gmail.com>]

mtd_add_partition() checks that 'length' is positive but does not
validate that 'offset + length' fits within the parent partition's
size. A userspace caller using the BLKPG_ADD_PARTITION ioctl can
supply a crafted large 'length' value that passes the length <= 0
check, causing add_mtd_device() to fire a WARN_ON() when it detects
the oversized partition.

Fix this by adding explicit bounds checks before allocate_partition()
is called:
  - Reject negative or out-of-range offsets.
  - Use u64 arithmetic to safely check offset + length <= parent_size,
    avoiding potential signed integer overflow.

Reported-by: syzbot+3ae80219c633aca5431c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=3ae80219c633aca5431c
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 drivers/mtd/mtdpart.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c
index 795a94e6b482..1a0e2207e440 100644
--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -264,6 +264,11 @@ int mtd_add_partition(struct mtd_info *parent, const char *name,
 	if (length <= 0)
 		return -EINVAL;
 
+	if (offset < 0 || offset >= (long long)parent_size)
+		return -EINVAL;
+
+	if ((u64)offset + (u64)length > parent_size)
+		return -EINVAL;
 	memset(&part, 0, sizeof(part));
 	part.name = name;
 	part.size = length;
-- 
2.43.0


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