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From:   Abdun Nihaal <abdun.nihaal@gmail.com>
To:     almaz.alexandrovich@paragon-software.com
Cc:     ntfs3@lists.linux.dev, linux-kernel@vger.kernel.org,
        skhan@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Abdun Nihaal <abdun.nihaal@gmail.com>,
        syzbot+f45957555ed4a808cc7a@syzkaller.appspotmail.com
Subject: [PATCH] fs/ntfs3: Fix NULL dereference in ni_write_inode
Date:   Sun, 30 Oct 2022 12:32:51 +0530
Message-Id: <20221030070251.614970-1-abdun.nihaal@gmail.com>
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Syzbot reports a NULL dereference in ni_write_inode.
When creating a new inode, if allocation fails in mi_init function
(called in mi_format_new function), mi->mrec is set to NULL.
In the error path of this inode creation, mi->mrec is later
dereferenced in ni_write_inode.

Add a NULL check to prevent NULL dereference.

Link: https://syzkaller.appspot.com/bug?extid=f45957555ed4a808cc7a
Reported-and-tested-by: syzbot+f45957555ed4a808cc7a@syzkaller.appspotmail.com
Signed-off-by: Abdun Nihaal <abdun.nihaal@gmail.com>
---
 fs/ntfs3/frecord.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
index 70a80f9412f7..e55bbd209ef8 100644
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -3243,6 +3243,9 @@ int ni_write_inode(struct inode *inode, int sync, const char *hint)
 		return 0;
 	}
 
+	if (!ni->mi.mrec)
+		goto out;
+
 	if (is_rec_inuse(ni->mi.mrec) &&
 	    !(sbi->flags & NTFS_FLAGS_LOG_REPLAYING) && inode->i_nlink) {
 		bool modified = false;
-- 
2.37.3