Re: [PATCH 1/8] quota: Allow to pass mount path to quotactl

[Jan Kara <jack@xxxxxxx>]

On Tue 28-01-20 11:06:31, Sascha Hauer wrote:
> Hi Jan,
> 
> On Mon, Jan 27, 2020 at 11:45:18AM +0100, Jan Kara wrote:
> > >  	cmds = cmd >> SUBCMDSHIFT;
> > >  	type = cmd & SUBCMDMASK;
> > >  
> > > +
> > 
> > Unnecessary empty line added...
> 
> Fixed
> 
> > > +	if (q_path) {
> > > +		ret = user_path_at(AT_FDCWD, special,
> > > +				   LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> > > +				   &sb_path);
> > > +		if (ret)
> > > +			goto out;
> > > +
> > > +		sb = sb_path.mnt->mnt_sb;
> > 
> > So I've realized that just looking up superblock with user_path_at() is not
> > enough. Quota code also expects that the superblock will be locked
> > (sb->s_umount) and filesystem will not be frozen (in case the quota
> > operation is going to modify the filesystem). This is needed to serialize
> > e.g. remount and quota operations or quota operations among themselves.
> > So you still need something like following to get superblock from the path:
> 
> Ok, here's an updated version. I'll send an update for the whole series
> when Richard had a look over it.
> 
> Sascha
> 
> ----------------------------8<-----------------------------
> 
> From 9c91395f2667c8a48f52a80896e559daf16f4a4c Mon Sep 17 00:00:00 2001
> From: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> Date: Wed, 30 Oct 2019 08:35:11 +0100
> Subject: [PATCH] quota: Allow to pass mount path to quotactl
> 
> This patch introduces the Q_PATH flag to the quotactl cmd argument.
> When given, the path given in the special argument to quotactl will
> be the mount path where the filesystem is mounted, instead of a path
> to the block device.
> This is necessary for filesystems which do not have a block device as
> backing store. Particularly this is done for upcoming UBIFS support.
> 
> Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>

Thanks. The patch looks good to me now. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/quota/quota.c           | 75 ++++++++++++++++++++++++++++++++------
>  include/uapi/linux/quota.h |  1 +
>  2 files changed, 64 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> index 5444d3c4d93f..712b71760f9d 100644
> --- a/fs/quota/quota.c
> +++ b/fs/quota/quota.c
> @@ -19,6 +19,7 @@
>  #include <linux/types.h>
>  #include <linux/writeback.h>
>  #include <linux/nospec.h>
> +#include <linux/mount.h>
>  
>  static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
>  				     qid_t id)
> @@ -810,6 +811,36 @@ static struct super_block *quotactl_block(const char __user *special, int cmd)
>  #endif
>  }
>  
> +static struct super_block *quotactl_path(const char __user *special, int cmd,
> +					 struct path *path)
> +{
> +	struct super_block *sb;
> +	int ret;
> +
> +	ret = user_path_at(AT_FDCWD, special, LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> +			   path);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	sb = path->mnt->mnt_sb;
> +restart:
> +	if (quotactl_cmd_onoff(cmd))
> +		down_write(&sb->s_umount);
> +	else
> +		down_read(&sb->s_umount);
> +
> +	if (quotactl_cmd_write(cmd) && sb->s_writers.frozen != SB_UNFROZEN) {
> +		if (quotactl_cmd_onoff(cmd))
> +			up_write(&sb->s_umount);
> +		else
> +			up_read(&sb->s_umount);
> +		wait_event(sb->s_writers.wait_unfrozen,
> +			   sb->s_writers.frozen == SB_UNFROZEN);
> +		goto restart;
> +	}
> +
> +	return sb;
> +}
>  /*
>   * This is the system call interface. This communicates with
>   * the user-level programs. Currently this only supports diskquota
> @@ -821,8 +852,9 @@ int kernel_quotactl(unsigned int cmd, const char __user *special,
>  {
>  	uint cmds, type;
>  	struct super_block *sb = NULL;
> -	struct path path, *pathp = NULL;
> +	struct path file_path, *file_pathp = NULL, sb_path;
>  	int ret;
> +	bool q_path;
>  
>  	cmds = cmd >> SUBCMDSHIFT;
>  	type = cmd & SUBCMDMASK;
> @@ -830,6 +862,9 @@ int kernel_quotactl(unsigned int cmd, const char __user *special,
>  	if (type >= MAXQUOTAS)
>  		return -EINVAL;
>  
> +	q_path = cmds & Q_PATH;
> +	cmds &= ~Q_PATH;
> +
>  	/*
>  	 * As a special case Q_SYNC can be called without a specific device.
>  	 * It will iterate all superblocks that have quota enabled and call
> @@ -847,28 +882,44 @@ int kernel_quotactl(unsigned int cmd, const char __user *special,
>  	 * resolution (think about autofs) and thus deadlocks could arise.
>  	 */
>  	if (cmds == Q_QUOTAON) {
> -		ret = user_path_at(AT_FDCWD, addr, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
> +		ret = user_path_at(AT_FDCWD, addr,
> +				   LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> +				   &file_path);
>  		if (ret)
> -			pathp = ERR_PTR(ret);
> +			file_pathp = ERR_PTR(ret);
>  		else
> -			pathp = &path;
> +			file_pathp = &file_path;
>  	}
>  
> -	sb = quotactl_block(special, cmds);
> +	if (q_path)
> +		sb = quotactl_path(special, cmds, &sb_path);
> +	else
> +		sb = quotactl_block(special, cmds);
> +
>  	if (IS_ERR(sb)) {
>  		ret = PTR_ERR(sb);
>  		goto out;
>  	}
>  
> -	ret = do_quotactl(sb, type, cmds, id, addr, pathp);
> +	ret = do_quotactl(sb, type, cmds, id, addr, file_pathp);
> +
> +	if (q_path) {
> +		if (quotactl_cmd_onoff(cmd))
> +			up_write(&sb->s_umount);
> +		else
> +			up_read(&sb->s_umount);
> +
> +		path_put(&sb_path);
> +	} else {
> +		if (!quotactl_cmd_onoff(cmds))
> +			drop_super(sb);
> +		else
> +			drop_super_exclusive(sb);
> +	}
>  
> -	if (!quotactl_cmd_onoff(cmds))
> -		drop_super(sb);
> -	else
> -		drop_super_exclusive(sb);
>  out:
> -	if (pathp && !IS_ERR(pathp))
> -		path_put(pathp);
> +	if (file_pathp && !IS_ERR(file_pathp))
> +		path_put(file_pathp);
>  	return ret;
>  }
>  
> diff --git a/include/uapi/linux/quota.h b/include/uapi/linux/quota.h
> index f17c9636a859..e1787c0df601 100644
> --- a/include/uapi/linux/quota.h
> +++ b/include/uapi/linux/quota.h
> @@ -71,6 +71,7 @@
>  #define Q_GETQUOTA 0x800007	/* get user quota structure */
>  #define Q_SETQUOTA 0x800008	/* set user quota structure */
>  #define Q_GETNEXTQUOTA 0x800009	/* get disk limits and usage >= ID */
> +#define Q_PATH     0x400000	/* quotactl special arg contains mount path */
>  
>  /* Quota format type IDs */
>  #define	QFMT_VFS_OLD 1
> -- 
> 2.25.0
> 
> 
> -- 
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-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR

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