[PATCH v2] udf: fix uninit-value use in udf_get_fileshortad

[Gianfranco Trad <gianf.trad@gmail.com>]

Check for overflow when computing alen in udf_current_aext to mitigate
later uninit-value use in udf_get_fileshortad KMSAN bug[1].
After applying the patch reproducer did not trigger any issue[2].

[1] https://syzkaller.appspot.com/bug?extid=8901c4560b7ab5c2f9df
[2] https://syzkaller.appspot.com/x/log.txt?x=10242227980000

Reported-by: syzbot+8901c4560b7ab5c2f9df@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8901c4560b7ab5c2f9df
Tested-by: syzbot+8901c4560b7ab5c2f9df@syzkaller.appspotmail.com
Suggested-by: Jan Kara <jack@suse.com>
Signed-off-by: Gianfranco Trad <gianf.trad@gmail.com>
---

Notes:
	changes in v2:
		- use check_add_overflow helper to check for overflow.
	
	link to v1: https://lore.kernel.org/all/20240919195227.412583-1-gianf.trad@gmail.com/T/

 fs/udf/inode.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 4726a4d014b6..811a035b600f 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -2215,9 +2215,10 @@ int8_t udf_current_aext(struct inode *inode, struct extent_position *epos,
 		if (!epos->offset)
 			epos->offset = sizeof(struct allocExtDesc);
 		ptr = epos->bh->b_data + epos->offset;
-		alen = sizeof(struct allocExtDesc) +
-			le32_to_cpu(((struct allocExtDesc *)epos->bh->b_data)->
-							lengthAllocDescs);
+		if (check_add_overflow(sizeof(struct allocExtDesc),
+					le32_to_cpu(((struct allocExtDesc *)epos->bh->b_data)
+						->lengthAllocDescs), &alen))
+			return -1;
 	}
 
 	switch (iinfo->i_alloc_type) {
-- 
2.43.0