Re: [PATCH] fs/ntfs3: fix null pointer dereference in d_flags_for_inode

[Almaz Alexandrovich <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>]

Hello.

Thank you for reporting this bug.
The bug happens because we don't initialize i_op for records in $Extend.
We tested patch on our side, let me know if patch helps you too.

    fs/ntfs3: Fix missing i_op in ntfs_read_mft
    
    There is null pointer dereference because i_op == NULL.
    The bug happens because we don't initialize i_op for records in $Extend.
    Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
    
    Reported-by: Liangbin Lian <jjm2473@xxxxxxxxx>
    Signed-off-by: Konstantin Komarov <almaz.alexandrovich@xxxxxxxxxxxxxxxxxxxx>

diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index 879952254071..b2cc1191be69 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -430,6 +430,7 @@ static struct inode *ntfs_read_mft(struct inode *inode,
        } else if (fname && fname->home.low == cpu_to_le32(MFT_REC_EXTEND) &&
                   fname->home.seq == cpu_to_le16(MFT_REC_EXTEND)) {
                /* Records in $Extend are not a files or general directories. */
+               inode->i_op = &ntfs_file_inode_operations;
        } else {
                err = -EINVAL;
                goto out;


On 5/6/22 06:46, Liangbin Lian wrote:
> ntfs_read_mft may return inode with null i_op, cause null pointer dereference in d_flags_for_inode (inode->i_op->get_link).
> Reproduce:
>   - sudo mount -t ntfs3 -o loop ntfs.img ntfs
>   - ls ntfs/'$Extend/$Quota'
>
> The call trace is shown below (striped):
>   BUG: kernel NULL pointer dereference, address: 0000000000000008
>   CPU: 0 PID: 577 Comm: ls Tainted: G           OE     5.16.0-0.bpo.4-amd64 #1  Debian 5.16.12-1~bpo11+1
>   RIP: 0010:d_flags_for_inode+0x65/0x90
>   Call Trace:
>   ntfs_lookup
>   +--- dir_search_u
>   |    +--- ntfs_iget5
>   |         +--- ntfs_read_mft
>   +--- d_splice_alias
>        +--- __d_add
>             +--- d_flags_for_inode
>
> Signed-off-by: Liangbin Lian <jjm2473@xxxxxxxxx>
> ---
>   fs/ntfs3/inode.c | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
> index 9eab11e3b..b68d26fa8 100644
> --- a/fs/ntfs3/inode.c
> +++ b/fs/ntfs3/inode.c
> @@ -45,7 +45,6 @@ static struct inode *ntfs_read_mft(struct inode *inode,
>   	struct MFT_REC *rec;
>   	struct runs_tree *run;
>   
> -	inode->i_op = NULL;
>   	/* Setup 'uid' and 'gid' */
>   	inode->i_uid = sbi->options->fs_uid;
>   	inode->i_gid = sbi->options->fs_gid;