From dc7ac6c4cae3b58724c2f1e21a7c05ce19ecd5a8 Mon Sep 17 00:00:00 2001
From: Wang Shilong <wangshilong1991@gmail.com>
Date: Wed, 3 Oct 2018 10:33:32 -0400
Subject: [PATCH] ext4: fix setattr project check in fssetxattr ioctl
Git-commit: dc7ac6c4cae3b58724c2f1e21a7c05ce19ecd5a8
Patch-mainline: v4.20-rc1
References: bsc#1117789

Currently, project quota could be changed by fssetxattr
ioctl, and existed permission check inode_owner_or_capable()
is obviously not enough, just think that common users could
change project id of file, that could make users to
break project quota easily.

This patch try to follow same regular of xfs project
Quota: 

"Project Quota ID state is only allowed to change from
within the init namespace. Enforce that restriction only
if we are trying to change the quota ID state.
Everything else is allowed in user namespaces."

Besides that, check and set project id'state should
be an atomic operation, protect whole operation with
inode lock, ext4_ioctl_setproject() is only used for
ioctl EXT4_IOC_FSSETXATTR, we have held mnt_want_write_file()
before ext4_ioctl_setflags(), and ext4_ioctl_setproject()
is called after ext4_ioctl_setflags(), we could share
codes, so remove it inside ext4_ioctl_setproject().

Signed-off-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/ext4/ioctl.c |   60 ++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 37 insertions(+), 23 deletions(-)

--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -346,25 +346,20 @@ static int ext4_ioctl_setproject(struct
 	if (projid_eq(kprojid, EXT4_I(inode)->i_projid))
 		return 0;
 
-	err = mnt_want_write_file(filp);
-	if (err)
-		return err;
-
 	err = -EPERM;
-	inode_lock(inode);
 	/* Is it quota file? Do not allow user to mess with it */
 	if (IS_NOQUOTA(inode))
-		goto out_unlock;
+		return err;
 
 	err = ext4_get_inode_loc(inode, &iloc);
 	if (err)
-		goto out_unlock;
+		return err;
 
 	raw_inode = ext4_raw_inode(&iloc);
 	if (!EXT4_FITS_IN_INODE(raw_inode, ei, i_projid)) {
 		err = -EOVERFLOW;
 		brelse(iloc.bh);
-		goto out_unlock;
+		return err;
 	}
 	brelse(iloc.bh);
 
@@ -373,10 +368,8 @@ static int ext4_ioctl_setproject(struct
 	handle = ext4_journal_start(inode, EXT4_HT_QUOTA,
 		EXT4_QUOTA_INIT_BLOCKS(sb) +
 		EXT4_QUOTA_DEL_BLOCKS(sb) + 3);
-	if (IS_ERR(handle)) {
-		err = PTR_ERR(handle);
-		goto out_unlock;
-	}
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
 
 	err = ext4_reserve_inode_write(handle, inode, &iloc);
 	if (err)
@@ -398,9 +391,6 @@ out_dirty:
 		err = rc;
 out_stop:
 	ext4_journal_stop(handle);
-out_unlock:
-	inode_unlock(inode);
-	mnt_drop_write_file(filp);
 	return err;
 }
 #else
@@ -585,6 +575,30 @@ static int ext4_ioc_getfsmap(struct supe
 	return 0;
 }
 
+static int ext4_ioctl_check_project(struct inode *inode, struct fsxattr *fa)
+{
+	/*
+	 * Project Quota ID state is only allowed to change from within the init
+	 * namespace. Enforce that restriction only if we are trying to change
+	 * the quota ID state. Everything else is allowed in user namespaces.
+	 */
+	if (current_user_ns() == &init_user_ns)
+		return 0;
+
+	if (__kprojid_val(EXT4_I(inode)->i_projid) != fa->fsx_projid)
+		return -EINVAL;
+
+	if (ext4_test_inode_flag(inode, EXT4_INODE_PROJINHERIT)) {
+		if (!(fa->fsx_xflags & FS_XFLAG_PROJINHERIT))
+			return -EINVAL;
+	} else {
+		if (fa->fsx_xflags & FS_XFLAG_PROJINHERIT)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
 long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -1022,19 +1036,19 @@ resizefs_out:
 			return err;
 
 		inode_lock(inode);
+		err = ext4_ioctl_check_project(inode, &fa);
+		if (err)
+			goto out;
 		flags = (ei->i_flags & ~EXT4_FL_XFLAG_VISIBLE) |
 			 (flags & EXT4_FL_XFLAG_VISIBLE);
 		err = ext4_ioctl_setflags(inode, flags);
-		inode_unlock(inode);
-		mnt_drop_write_file(filp);
 		if (err)
-			return err;
-
+			goto out;
 		err = ext4_ioctl_setproject(filp, fa.fsx_projid);
-		if (err)
-			return err;
-
-		return 0;
+out:
+		inode_unlock(inode);
+		mnt_drop_write_file(filp);
+		return err;
 	}
 	case EXT4_IOC_SHUTDOWN:
 		return ext4_shutdown(sb, arg);