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authorChristian Brauner <christian.brauner@ubuntu.com>2021-01-21 14:19:57 +0100
committerChristian Brauner <christian.brauner@ubuntu.com>2021-01-24 14:43:46 +0100
commit14f3db5542e62bcf6fe088a09760ac52d55306c5 (patch)
tree98244136b2eaf9e8700beb4a6feab2808c4a0cdf /fs/ext4/ioctl.c
parent4b78993681083361f19f66b4e9db298945647a3d (diff)
ext4: support idmapped mounts
Enable idmapped mounts for ext4. All dedicated helpers we need for this exist. So this basically just means we're passing down the user_namespace argument from the VFS methods to the relevant helpers. Let's create simple example where we idmap an ext4 filesystem: root@f2-vm:~# truncate -s 5G ext4.img root@f2-vm:~# mkfs.ext4 ./ext4.img mke2fs 1.45.5 (07-Jan-2020) Discarding device blocks: done Creating filesystem with 1310720 4k blocks and 327680 inodes Filesystem UUID: 3fd91794-c6ca-4b0f-9964-289a000919cf Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736 Allocating group tables: done Writing inode tables: done Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: done root@f2-vm:~# losetup -f --show ./ext4.img /dev/loop0 root@f2-vm:~# mount /dev/loop0 /mnt root@f2-vm:~# ls -al /mnt/ total 24 drwxr-xr-x 3 root root 4096 Oct 28 13:34 . drwxr-xr-x 30 root root 4096 Oct 28 13:22 .. drwx------ 2 root root 16384 Oct 28 13:34 lost+found # Let's create an idmapped mount at /idmapped1 where we map uid and gid # 0 to uid and gid 1000 root@f2-vm:/# ./mount-idmapped --map-mount b:0:1000:1 /mnt/ /idmapped1/ root@f2-vm:/# ls -al /idmapped1/ total 24 drwxr-xr-x 3 ubuntu ubuntu 4096 Oct 28 13:34 . drwxr-xr-x 30 root root 4096 Oct 28 13:22 .. drwx------ 2 ubuntu ubuntu 16384 Oct 28 13:34 lost+found # Let's create an idmapped mount at /idmapped2 where we map uid and gid # 0 to uid and gid 2000 root@f2-vm:/# ./mount-idmapped --map-mount b:0:2000:1 /mnt/ /idmapped2/ root@f2-vm:/# ls -al /idmapped2/ total 24 drwxr-xr-x 3 2000 2000 4096 Oct 28 13:34 . drwxr-xr-x 31 root root 4096 Oct 28 13:39 .. drwx------ 2 2000 2000 16384 Oct 28 13:34 lost+found Let's create another example where we idmap the rootfs filesystem without a mapping for uid 0 and gid 0: # Create an idmapped mount of for a full POSIX range of rootfs under # /mnt but without a mapping for uid 0 to reduce attack surface root@f2-vm:/# ./mount-idmapped --map-mount b:1:1:65536 / /mnt/ # Since we don't have a mapping for uid and gid 0 all files owned by # uid and gid 0 should show up as uid and gid 65534: root@f2-vm:/# ls -al /mnt/ total 664 drwxr-xr-x 31 nobody nogroup 4096 Oct 28 13:39 . drwxr-xr-x 31 root root 4096 Oct 28 13:39 .. lrwxrwxrwx 1 nobody nogroup 7 Aug 25 07:44 bin -> usr/bin drwxr-xr-x 4 nobody nogroup 4096 Oct 28 13:17 boot drwxr-xr-x 2 nobody nogroup 4096 Aug 25 07:48 dev drwxr-xr-x 81 nobody nogroup 4096 Oct 28 04:00 etc drwxr-xr-x 4 nobody nogroup 4096 Oct 28 04:00 home lrwxrwxrwx 1 nobody nogroup 7 Aug 25 07:44 lib -> usr/lib lrwxrwxrwx 1 nobody nogroup 9 Aug 25 07:44 lib32 -> usr/lib32 lrwxrwxrwx 1 nobody nogroup 9 Aug 25 07:44 lib64 -> usr/lib64 lrwxrwxrwx 1 nobody nogroup 10 Aug 25 07:44 libx32 -> usr/libx32 drwx------ 2 nobody nogroup 16384 Aug 25 07:47 lost+found drwxr-xr-x 2 nobody nogroup 4096 Aug 25 07:44 media drwxr-xr-x 31 nobody nogroup 4096 Oct 28 13:39 mnt drwxr-xr-x 2 nobody nogroup 4096 Aug 25 07:44 opt drwxr-xr-x 2 nobody nogroup 4096 Apr 15 2020 proc drwx--x--x 6 nobody nogroup 4096 Oct 28 13:34 root drwxr-xr-x 2 nobody nogroup 4096 Aug 25 07:46 run lrwxrwxrwx 1 nobody nogroup 8 Aug 25 07:44 sbin -> usr/sbin drwxr-xr-x 2 nobody nogroup 4096 Aug 25 07:44 srv drwxr-xr-x 2 nobody nogroup 4096 Apr 15 2020 sys drwxrwxrwt 10 nobody nogroup 4096 Oct 28 13:19 tmp drwxr-xr-x 14 nobody nogroup 4096 Oct 20 13:00 usr drwxr-xr-x 12 nobody nogroup 4096 Aug 25 07:45 var # Since we do have a mapping for uid and gid 1000 all files owned by # uid and gid 1000 should simply show up as uid and gid 1000: root@f2-vm:/# ls -al /mnt/home/ubuntu/ total 40 drwxr-xr-x 3 ubuntu ubuntu 4096 Oct 28 00:43 . drwxr-xr-x 4 nobody nogroup 4096 Oct 28 04:00 .. -rw------- 1 ubuntu ubuntu 2936 Oct 28 12:26 .bash_history -rw-r--r-- 1 ubuntu ubuntu 220 Feb 25 2020 .bash_logout -rw-r--r-- 1 ubuntu ubuntu 3771 Feb 25 2020 .bashrc -rw-r--r-- 1 ubuntu ubuntu 807 Feb 25 2020 .profile -rw-r--r-- 1 ubuntu ubuntu 0 Oct 16 16:11 .sudo_as_admin_successful -rw------- 1 ubuntu ubuntu 1144 Oct 28 00:43 .viminfo Link: https://lore.kernel.org/r/20210121131959.646623-39-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-ext4@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Diffstat (limited to 'fs/ext4/ioctl.c')
-rw-r--r--fs/ext4/ioctl.c19
1 files changed, 11 insertions, 8 deletions
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index ab80e2493fdc..56ad9c4b6350 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -107,10 +107,12 @@ void ext4_reset_inode_seed(struct inode *inode)
* important fields of the inodes.
*
* @sb: the super block of the filesystem
+ * @mnt_userns: user namespace of the mount the inode was found from
* @inode: the inode to swap with EXT4_BOOT_LOADER_INO
*
*/
static long swap_inode_boot_loader(struct super_block *sb,
+ struct user_namespace *mnt_userns,
struct inode *inode)
{
handle_t *handle;
@@ -139,7 +141,7 @@ static long swap_inode_boot_loader(struct super_block *sb,
}
if (IS_RDONLY(inode) || IS_APPEND(inode) || IS_IMMUTABLE(inode) ||
- !inode_owner_or_capable(&init_user_ns, inode) ||
+ !inode_owner_or_capable(mnt_userns, inode) ||
!capable(CAP_SYS_ADMIN)) {
err = -EPERM;
goto journal_err_out;
@@ -815,6 +817,7 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
struct inode *inode = file_inode(filp);
struct super_block *sb = inode->i_sb;
struct ext4_inode_info *ei = EXT4_I(inode);
+ struct user_namespace *mnt_userns = file_mnt_user_ns(filp);
unsigned int flags;
ext4_debug("cmd = %u, arg = %lu\n", cmd, arg);
@@ -830,7 +833,7 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
case FS_IOC_SETFLAGS: {
int err;
- if (!inode_owner_or_capable(&init_user_ns, inode))
+ if (!inode_owner_or_capable(mnt_userns, inode))
return -EACCES;
if (get_user(flags, (int __user *) arg))
@@ -872,7 +875,7 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
__u32 generation;
int err;
- if (!inode_owner_or_capable(&init_user_ns, inode))
+ if (!inode_owner_or_capable(mnt_userns, inode))
return -EPERM;
if (ext4_has_metadata_csum(inode->i_sb)) {
@@ -1011,7 +1014,7 @@ mext_out:
case EXT4_IOC_MIGRATE:
{
int err;
- if (!inode_owner_or_capable(&init_user_ns, inode))
+ if (!inode_owner_or_capable(mnt_userns, inode))
return -EACCES;
err = mnt_want_write_file(filp);
@@ -1033,7 +1036,7 @@ mext_out:
case EXT4_IOC_ALLOC_DA_BLKS:
{
int err;
- if (!inode_owner_or_capable(&init_user_ns, inode))
+ if (!inode_owner_or_capable(mnt_userns, inode))
return -EACCES;
err = mnt_want_write_file(filp);
@@ -1052,7 +1055,7 @@ mext_out:
err = mnt_want_write_file(filp);
if (err)
return err;
- err = swap_inode_boot_loader(sb, inode);
+ err = swap_inode_boot_loader(sb, mnt_userns, inode);
mnt_drop_write_file(filp);
return err;
}
@@ -1218,7 +1221,7 @@ resizefs_out:
case EXT4_IOC_CLEAR_ES_CACHE:
{
- if (!inode_owner_or_capable(&init_user_ns, inode))
+ if (!inode_owner_or_capable(mnt_userns, inode))
return -EACCES;
ext4_clear_inode_es(inode);
return 0;
@@ -1264,7 +1267,7 @@ resizefs_out:
return -EFAULT;
/* Make sure caller has proper permission */
- if (!inode_owner_or_capable(&init_user_ns, inode))
+ if (!inode_owner_or_capable(mnt_userns, inode))
return -EACCES;
if (fa.fsx_xflags & ~EXT4_SUPPORTED_FS_XFLAGS)