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

On 30.10.2022 11:02, Abdun Nihaal wrote:
> 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;
Thank you for your work, applied!