linux-kernel - Re: [PATCH] fs/ntfs3: fix null pointer dereference in d_flags_for

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Date:   Thu, 26 May 2022 13:22:27 +0300
From:   Almaz Alexandrovich <almaz.alexandrovich@...agon-software.com>
To:     Liangbin Lian <jjm2473@...il.com>, <ntfs3@...ts.linux.dev>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs/ntfs3: fix null pointer dereference in
 d_flags_for_inode

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@...il.com>
     Signed-off-by: Konstantin Komarov <almaz.alexandrovich@...agon-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@...il.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;