[PATCH 1/2] quota: Add mountpath based quota support

Sascha Hauer
2021-02-11T16:36:56Z

Add syscall quotactl_path, a variant of quotactl which allows to specify
the mountpath instead of a path of to a block device.

The quotactl syscall expects a path to the mounted block device to
specify the filesystem to work on. This limits usage to filesystems
which actually have a block device. quotactl_path replaces the path
to the block device with a path where the filesystem is mounted at.

The global Q_SYNC command to sync all filesystems is not supported for
this new syscall, otherwise quotactl_path behaves like quotactl.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
fs/quota/quota.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)

diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index 6d16b2be5ac4..6f1df32abeea 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -17,6 +17,7 @@
#include <linux/capability.h>
#include <linux/quotaops.h>
#include <linux/types.h>
+#include <linux/mount.h>
#include <linux/writeback.h>
#include <linux/nospec.h>
#include "compat.h"
@@ -968,3 +969,51 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special,
path_put(pathp);
return ret;
}
+
+SYSCALL_DEFINE4(quotactl_path, unsigned int, cmd, const char __user *,
+ mountpoint, qid_t, id, void __user *, addr)
+{
+ struct super_block *sb;
+ struct path mountpath;
+ unsigned int cmds = cmd >> SUBCMDSHIFT;
+ unsigned int type = cmd & SUBCMDMASK;
+ int ret;
+
+ if (type >= MAXQUOTAS)
+ return -EINVAL;
+
+ if (!mountpoint)
+ return -ENODEV;
+
+ ret = user_path_at(AT_FDCWD, mountpoint,
+ LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT, &mountpath);
+ if (ret)
+ return ret;
+
+ sb = mountpath.dentry->d_inode->i_sb;
+
+ if (quotactl_cmd_write(cmds)) {
+ ret = mnt_want_write(mountpath.mnt);
+ if (ret)
+ goto out;
+ }
+
+ if (quotactl_cmd_onoff(cmds))
+ down_write(&sb->s_umount);
+ else
+ down_read(&sb->s_umount);
+
+ ret = do_quotactl(sb, type, cmds, id, addr, ERR_PTR(-EINVAL));
+
+ if (quotactl_cmd_onoff(cmds))
+ up_write(&sb->s_umount);
+ else
+ up_read(&sb->s_umount);
+
+ if (quotactl_cmd_write(cmds))
+ mnt_drop_write(mountpath.mnt);
+out:
+ path_put(&mountpath);
+
+ return ret;
+}
--
2.20.1