linux-kernel - Re: [PATCH] Abort file_remove

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Date:   Mon, 17 Dec 2018 09:28:00 +0100
From:   Jan Kara <jack@...e.cz>
To:     Alexander Lochmann <alexander.lochmann@...dortmund.de>
Cc:     Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Horst Schirmeier <horst.schirmeier@...dortmund.de>
Subject: Re: [PATCH] Abort file_remove_privs() for non-reg. files

On Fri 14-12-18 11:55:52, Alexander Lochmann wrote:
> 
> file_remove_privs() might be called for non-regular files, e.g.
> blkdev inode. There is no reason to do its job on things
> like blkdev inodes, pipes, or cdevs. Hence, abort if
> file does not refer to a regular inode.
> The following stacktrace shows how to get there:
> 13: entry_SYSENTER_32:460
> 12: do_fast_syscall_32:410
> 11: _static_cpu_has:146
> 10: do_syscall_32_irqs_on:322
> 09: SyS_pwrite64:636
> 08: SYSC_pwrite64:650
> 07: fdput:38
> 06: vfs_write:560
> 05: __vfs_write:512
> 04: new_sync_write:500
> 03: blkdev_write_iter:1977
> 02: __generic_file_write_iter:2897
> 01: file_remove_privs:1818
> 00: inode_has_no_xattr:3163
> 
> Found by LockDoc (Alexander Lochmann, Horst Schirmeier and Olaf
> Spinczyk)
> 
> Signed-off-by: Alexander Lochmann <alexander.lochmann@...dortmund.de>
> Signed-off-by: Horst Schirmeier <horst.schirmeier@...dortmund.de>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/inode.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 35d2108d567c..682088190413 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1820,8 +1820,13 @@ int file_remove_privs(struct file *file)
>  	int kill;
>  	int error = 0;
> 
> -	/* Fast path for nothing security related */
> -	if (IS_NOSEC(inode))
> +	/*
> +	 * Fast path for nothing security related.
> +	 * As well for non-regular files, e.g. blkdev inodes.
> +	 * For example, blkdev_write_iter() might get here
> +	 * trying to remove privs which it is not allowed to.
> +	 */
> +	if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
>  		return 0;
> 
>  	kill = dentry_needs_remove_privs(dentry);
> -- 
> 2.19.2
> 



-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR