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

Almaz Alexandrovich
2022-05-26T10:28:50Z

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@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

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@gmail.com>
> ---
> 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;