[PATCH v2 2/4] squashfs: Fix integer overflow in sqfs_inode_size()

[Richard Weinberger <richard@nod.at>]

A carefully crafted squashfs filesystem can exhibit an extremly large
inode size and overflow the calculation in sqfs_inode_size().
As a consequence, the squashfs driver will read from wrong locations.

Fix by using __builtin_add_overflow() to detect the overflow.

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
---
 fs/squashfs/sqfs_inode.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/squashfs/sqfs_inode.c b/fs/squashfs/sqfs_inode.c
index d25cfb53e7..bb3ccd37e3 100644
--- a/fs/squashfs/sqfs_inode.c
+++ b/fs/squashfs/sqfs_inode.c
@@ -78,11 +78,16 @@ int sqfs_inode_size(struct squashfs_base_inode *inode, u32 blk_size)
 
 	case SQFS_SYMLINK_TYPE:
 	case SQFS_LSYMLINK_TYPE: {
+		int size;
+
 		struct squashfs_symlink_inode *symlink =
 			(struct squashfs_symlink_inode *)inode;
 
-		return sizeof(*symlink) +
-			get_unaligned_le32(&symlink->symlink_size);
+		if (__builtin_add_overflow(sizeof(*symlink),
+		    get_unaligned_le32(&symlink->symlink_size), &size))
+			return -EINVAL;
+
+		return size;
 	}
 
 	case SQFS_BLKDEV_TYPE:
-- 
2.35.3