Re: [PATCH] fs/ntfs3: Fix null-ptr-deref on inode->i_op in ntfs_lookup()

[Konstantin Komarov]

On 25.11.2022 14:21, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
>
> Syzbot reported a null-ptr-deref bug:
>
> ntfs3: loop0: Different NTFS' sector size (1024) and media sector size
> (512)
> ntfs3: loop0: Mark volume as dirty due to NTFS errors
> general protection fault, probably for non-canonical address
> 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> RIP: 0010:d_flags_for_inode fs/dcache.c:1980 [inline]
> RIP: 0010:__d_add+0x5ce/0x800 fs/dcache.c:2796
> Call Trace:
>   <TASK>
>   d_splice_alias+0x122/0x3b0 fs/dcache.c:3191
>   lookup_open fs/namei.c:3391 [inline]
>   open_last_lookups fs/namei.c:3481 [inline]
>   path_openat+0x10e6/0x2df0 fs/namei.c:3688
>   do_filp_open+0x264/0x4f0 fs/namei.c:3718
>   do_sys_openat2+0x124/0x4e0 fs/open.c:1310
>   do_sys_open fs/open.c:1326 [inline]
>   __do_sys_open fs/open.c:1334 [inline]
>   __se_sys_open fs/open.c:1330 [inline]
>   __x64_sys_open+0x221/0x270 fs/open.c:1330
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> If the MFT record of ntfs inode is not a base record, inode->i_op can be
> NULL. And a null-ptr-deref may happen:
>
> ntfs_lookup()
>      dir_search_u() # inode->i_op is set to NULL
>      d_splice_alias()
>          __d_add()
>              d_flags_for_inode() # inode->i_op->get_link null-ptr-deref
>
> Fix this by adding a Check on inode->i_op before calling the
> d_splice_alias() function.
>
> Fixes: 4342306f0f0d ("fs/ntfs3: Add file operations and implementation")
> Reported-by: syzbot+a8f26a403c169b7593fe@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> ---
>   fs/ntfs3/namei.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/fs/ntfs3/namei.c b/fs/ntfs3/namei.c
> index bc22cc321a74..7760aedc0672 100644
> --- a/fs/ntfs3/namei.c
> +++ b/fs/ntfs3/namei.c
> @@ -86,6 +86,16 @@ static struct dentry *ntfs_lookup(struct inode *dir, struct dentry *dentry,
>   		__putname(uni);
>   	}
>   
> +	/*
> +	 * Check for a null pointer
> +	 * If the MFT record of ntfs inode is not a base record, inode->i_op can be NULL.
> +	 * This causes null pointer dereference in d_splice_alias().
> +	 */
> +	if (!IS_ERR(inode) && inode->i_op == NULL) {
> +		iput(inode);
> +		inode = ERR_PTR(-EINVAL);
> +	}
> +
>   	return d_splice_alias(inode, dentry);
>   }
>   
Applied, thanks!