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>
---
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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