Re: [PATCH] fs: ntfs3: Fix a possible null-pointer dereference in ni_clear()

[Konstantin Komarov <almaz.alexandrovich@paragon-software.com>]

In a previous commit c1006bd13146, ni->mi.mrec in ni_write_inode()
> could be NULL, and thus a NULL check is added for this variable.
>
> However, in the same call stack, ni->mi.mrec can be also dereferenced
> in ni_clear():
>
> ntfs_evict_inode(inode)
>    ni_write_inode(inode, ...)
>      ni = ntfs_i(inode);
>      is_rec_inuse(ni->mi.mrec) -> Add a NULL check by previous commit
>    ni_clear(ntfs_i(inode))
>      is_rec_inuse(ni->mi.mrec) -> No check
>
> Thus, a possible null-pointer dereference may exist in ni_clear().
> To fix it, a NULL check is added in this function.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
> ---
>   fs/ntfs3/frecord.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ntfs3/frecord.c b/fs/ntfs3/frecord.c
> index f1df52dfab74..046ec4179d75 100644
> --- a/fs/ntfs3/frecord.c
> +++ b/fs/ntfs3/frecord.c
> @@ -102,7 +102,7 @@ void ni_clear(struct ntfs_inode *ni)
>   {
>   	struct rb_node *node;
>   
> -	if (!ni->vfs_inode.i_nlink && is_rec_inuse(ni->mi.mrec))
> +	if (!ni->vfs_inode.i_nlink && ni->mi.mrec && is_rec_inuse(ni->mi.mrec))
>   		ni_delete_all(ni);
>   
>   	al_destroy(ni);

I apologize for the delayed response.

Thank you for your work, applied!