[PATCH] hostfs: handle idmapped mounts

From: Glenn Washburn <development@efficientek.com>
To: linux-um <linux-um@lists.infradead.org>,
	Richard Weinberger <richard@nod.at>,
	Johannes Berg <johannes@sipsolutions.net>,
	Anton Ivanov <anton.ivanov@kot-begemot.co.uk>
Cc: Glenn Washburn <development@efficientek.com>
Subject: [PATCH] hostfs: handle idmapped mounts
Date: Fri, 27 Jan 2023 19:41:59 -0600	[thread overview]
Message-ID: <20230128014159.1741728-1-development@efficientek.com> (raw)

Let hostfs handle idmapped mounts. This allows to have the same hostfs
mount appear in multiple locations with different id mappings.

root@(none):/media# id
uid=0(root) gid=0(root) groups=0(root)
root@(none):/media# mkdir mnt idmapped
root@(none):/media# mount -thostfs -o/home/user hostfs mnt

root@(none):/media# touch mnt/aaa
root@(none):/media# mount-idmapped --map-mount u:`id -u user`:0:1 --map-mount g:`id -g user`:0:1 /media/mnt /media/idmapped
root@(none):/media# ls -l mnt/aaa idmapped/aaa
-rw-r--r-- 1 root root 0 Jan 28 01:23 idmapped/aaa
-rw-r--r-- 1 user user 0 Jan 28 01:23 mnt/aaa

root@(none):/media# touch idmapped/bbb
root@(none):/media# ls -l mnt/bbb idmapped/bbb
-rw-r--r-- 1 root root 0 Jan 28 01:26 idmapped/bbb
-rw-r--r-- 1 user user 0 Jan 28 01:26 mnt/bbb

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 fs/hostfs/hostfs_kern.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index cc1bc6f93a01..876b73e05ac1 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -786,7 +786,7 @@ static int hostfs_permission(struct user_namespace *mnt_userns,
 		err = access_file(name, r, w, x);
 	__putname(name);
 	if (!err)
-		err = generic_permission(&init_user_ns, ino, desired);
+		err = generic_permission(mnt_userns, ino, desired);
 	return err;
 }
 
@@ -800,7 +800,7 @@ static int hostfs_setattr(struct user_namespace *mnt_userns,
 
 	int fd = HOSTFS_I(inode)->fd;
 
-	err = setattr_prepare(&init_user_ns, dentry, attr);
+	err = setattr_prepare(mnt_userns, dentry, attr);
 	if (err)
 		return err;
 
@@ -814,11 +814,11 @@ static int hostfs_setattr(struct user_namespace *mnt_userns,
 	}
 	if (attr->ia_valid & ATTR_UID) {
 		attrs.ia_valid |= HOSTFS_ATTR_UID;
-		attrs.ia_uid = from_kuid(&init_user_ns, attr->ia_uid);
+		attrs.ia_uid = from_kuid(mnt_userns, attr->ia_uid);
 	}
 	if (attr->ia_valid & ATTR_GID) {
 		attrs.ia_valid |= HOSTFS_ATTR_GID;
-		attrs.ia_gid = from_kgid(&init_user_ns, attr->ia_gid);
+		attrs.ia_gid = from_kgid(mnt_userns, attr->ia_gid);
 	}
 	if (attr->ia_valid & ATTR_SIZE) {
 		attrs.ia_valid |= HOSTFS_ATTR_SIZE;
@@ -857,7 +857,7 @@ static int hostfs_setattr(struct user_namespace *mnt_userns,
 	    attr->ia_size != i_size_read(inode))
 		truncate_setsize(inode, attr->ia_size);
 
-	setattr_copy(&init_user_ns, inode, attr);
+	setattr_copy(mnt_userns, inode, attr);
 	mark_inode_dirty(inode);
 	return 0;
 }
@@ -991,7 +991,7 @@ static struct file_system_type hostfs_type = {
 	.name 		= "hostfs",
 	.mount	 	= hostfs_read_sb,
 	.kill_sb	= hostfs_kill_sb,
-	.fs_flags 	= 0,
+	.fs_flags 	= FS_ALLOW_IDMAP,
 };
 MODULE_ALIAS_FS("hostfs");
 
-- 
2.30.2


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