[PATCH 5.10.y 1/2] udf: fix uninit-value use in udf_get_fileshortad

[Sasha Levin <sashal@kernel.org>]

From: Gianfranco Trad <gianf.trad@gmail.com>

[ Upstream commit 264db9d666ad9a35075cc9ed9ec09d021580fbb1 ]

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>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20240925074613.8475-3-gianf.trad@gmail.com
Stable-dep-of: 3bd5e45c2ce3 ("fs: udf: fix OOB read in lengthAllocDescs handling")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/udf/inode.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index 499a27372a40b..f6dbd65b8559c 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -2190,12 +2190,15 @@ int8_t udf_current_aext(struct inode *inode, struct extent_position *epos,
 		alen = udf_file_entry_alloc_offset(inode) +
 							iinfo->i_lenAlloc;
 	} else {
+		struct allocExtDesc *header =
+			(struct allocExtDesc *)epos->bh->b_data;
+
 		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(header->lengthAllocDescs), &alen))
+			return -1;
 	}
 
 	switch (iinfo->i_alloc_type) {
-- 
2.51.0