linux-kernel - Re: [syzbot] [hfs?] KMSAN: uninit-value in hfs_read

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Message-ID: <20241122221953.18329-1-leocstone@gmail.com>
Date: Fri, 22 Nov 2024 14:19:50 -0800
From: Leo Stone <leocstone@...il.com>
To: syzbot+2db3c7526ba68f4ea776@...kaller.appspotmail.com,
	brauner@...nel.org,
	quic_jjohnson@...cinc.com,
	jack@...e.cz,
	viro@...iv.linux.org.uk,
	sandeen@...hat.com
Cc: Leo Stone <leocstone@...il.com>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [hfs?] KMSAN: uninit-value in hfs_read_inode

After the call to hfs_bnode_read on line 356 of fs/hfs/super.c, the
struct hfs_cat_rec, which is supposed to be for the root dir, has
type HFS_CDR_FIL. Only the first 70 bytes of that struct are then
initialized, because the entrylength passed into hfs_bnode_read is
70, corresponding to the size of struct hfs_cat_dir. This causes
uninitialized values to be used later on when the hfs_cat_rec
union is treated as a hfs_cat_file.

Add a check to make sure the retrieved record has the correct type
for the root directory (HFS_CDR_DIR).

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

---
 fs/hfs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index 3bee9b5dba5e..02d78992eefd 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -354,6 +354,8 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
 			goto bail_hfs_find;
 		}
 		hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
+		if (rec.type != HFS_CDR_DIR)
+			res = -EIO;
 	}
 	if (res)
 		goto bail_hfs_find;
-- 
2.43.0