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>

diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c
index 059434e..c5eaffc 100644 (file)
--- a/fs/ext4/acl.c
+++ b/fs/ext4/acl.c
@@ -246,8 +246,7 @@ retry:
        ext4_fc_start_update(inode);
 
        if ((type == ACL_TYPE_ACCESS) && acl) {
-               error = posix_acl_update_mode(&init_user_ns, inode, &mode,
-                                             &acl);
+               error = posix_acl_update_mode(mnt_userns, inode, &mode, &acl);
                if (error)
                        goto out_stop;
                if (mode != inode->i_mode)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 3c750f5..644fd69 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2755,18 +2755,19 @@ extern int ext4fs_dirhash(const struct inode *dir, const char *name, int len,
 
 /* ialloc.c */
 extern int ext4_mark_inode_used(struct super_block *sb, int ino);
-extern struct inode *__ext4_new_inode(handle_t *, struct inode *, umode_t,
+extern struct inode *__ext4_new_inode(struct user_namespace *, handle_t *,
+                                     struct inode *, umode_t,
                                      const struct qstr *qstr, __u32 goal,
                                      uid_t *owner, __u32 i_flags,
                                      int handle_type, unsigned int line_no,
                                      int nblocks);
 
-#define ext4_new_inode(handle, dir, mode, qstr, goal, owner, i_flags) \
-       __ext4_new_inode((handle), (dir), (mode), (qstr), (goal), (owner), \
-                        i_flags, 0, 0, 0)
-#define ext4_new_inode_start_handle(dir, mode, qstr, goal, owner, \
+#define ext4_new_inode(handle, dir, mode, qstr, goal, owner, i_flags)          \
+       __ext4_new_inode(&init_user_ns, (handle), (dir), (mode), (qstr),       \
+                        (goal), (owner), i_flags, 0, 0, 0)
+#define ext4_new_inode_start_handle(mnt_userns, dir, mode, qstr, goal, owner, \
                                    type, nblocks)                  \
-       __ext4_new_inode(NULL, (dir), (mode), (qstr), (goal), (owner), \
+       __ext4_new_inode((mnt_userns), NULL, (dir), (mode), (qstr), (goal), (owner), \
                         0, (type), __LINE__, (nblocks))
 
 

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 00c1ec6..bf90289 100644 (file)
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -919,7 +919,8 @@ static int ext4_xattr_credits_for_new_inode(struct inode *dir, mode_t mode,
  * For other inodes, search forward from the parent directory's block
  * group to find a free inode.
  */
-struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
+struct inode *__ext4_new_inode(struct user_namespace *mnt_userns,
+                              handle_t *handle, struct inode *dir,
                               umode_t mode, const struct qstr *qstr,
                               __u32 goal, uid_t *owner, __u32 i_flags,
                               int handle_type, unsigned int line_no,
@@ -969,10 +970,10 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
                i_gid_write(inode, owner[1]);
        } else if (test_opt(sb, GRPID)) {
                inode->i_mode = mode;
-               inode->i_uid = current_fsuid();
+               inode->i_uid = fsuid_into_mnt(mnt_userns);
                inode->i_gid = dir->i_gid;
        } else
-               inode_init_owner(&init_user_ns, inode, dir, mode);
+               inode_init_owner(mnt_userns, inode, dir, mode);
 
        if (ext4_has_feature_project(sb) &&
            ext4_test_inode_flag(dir, EXT4_INODE_PROJINHERIT))

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ce45535..8fbf85b 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -20,6 +20,7 @@
  */
 
 #include <linux/fs.h>
+#include <linux/mount.h>
 #include <linux/time.h>
 #include <linux/highuid.h>
 #include <linux/pagemap.h>
@@ -5338,7 +5339,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
                                  ATTR_GID | ATTR_TIMES_SET))))
                return -EPERM;
 
-       error = setattr_prepare(&init_user_ns, dentry, attr);
+       error = setattr_prepare(mnt_userns, dentry, attr);
        if (error)
                return error;
 
@@ -5513,7 +5514,7 @@ out_mmap_sem:
        }
 
        if (!error) {
-               setattr_copy(&init_user_ns, inode, attr);
+               setattr_copy(mnt_userns, inode, attr);
                mark_inode_dirty(inode);
        }
 
@@ -5525,7 +5526,7 @@ out_mmap_sem:
                ext4_orphan_del(NULL, inode);
 
        if (!error && (ia_valid & ATTR_MODE))
-               rc = posix_acl_chmod(&init_user_ns, inode, inode->i_mode);
+               rc = posix_acl_chmod(mnt_userns, inode, inode->i_mode);
 
 err_out:
        if  (error)
@@ -5572,7 +5573,7 @@ int ext4_getattr(struct user_namespace *mnt_userns, const struct path *path,
                                  STATX_ATTR_NODUMP |
                                  STATX_ATTR_VERITY);
 
-       generic_fillattr(&init_user_ns, inode, stat);
+       generic_fillattr(mnt_userns, inode, stat);
        return 0;
 }
 
@@ -5583,7 +5584,7 @@ int ext4_file_getattr(struct user_namespace *mnt_userns,
        struct inode *inode = d_inode(path->dentry);
        u64 delalloc_blocks;
 
-       ext4_getattr(&init_user_ns, path, stat, request_mask, query_flags);
+       ext4_getattr(mnt_userns, path, stat, request_mask, query_flags);
 
        /*
         * If there is inline data in the inode, the inode will normally not

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index ab80e24..56ad9c4 100644 (file)
--- 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)

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 13dff80..877c602 100644 (file)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2610,8 +2610,8 @@ static int ext4_create(struct user_namespace *mnt_userns, struct inode *dir,
        credits = (EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
                   EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3);
 retry:
-       inode = ext4_new_inode_start_handle(dir, mode, &dentry->d_name, 0,
-                                           NULL, EXT4_HT_DIR, credits);
+       inode = ext4_new_inode_start_handle(mnt_userns, dir, mode, &dentry->d_name,
+                                           0, NULL, EXT4_HT_DIR, credits);
        handle = ext4_journal_current_handle();
        err = PTR_ERR(inode);
        if (!IS_ERR(inode)) {
@@ -2645,8 +2645,8 @@ static int ext4_mknod(struct user_namespace *mnt_userns, struct inode *dir,
        credits = (EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
                   EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3);
 retry:
-       inode = ext4_new_inode_start_handle(dir, mode, &dentry->d_name, 0,
-                                           NULL, EXT4_HT_DIR, credits);
+       inode = ext4_new_inode_start_handle(mnt_userns, dir, mode, &dentry->d_name,
+                                           0, NULL, EXT4_HT_DIR, credits);
        handle = ext4_journal_current_handle();
        err = PTR_ERR(inode);
        if (!IS_ERR(inode)) {
@@ -2677,7 +2677,7 @@ static int ext4_tmpfile(struct user_namespace *mnt_userns, struct inode *dir,
                return err;
 
 retry:
-       inode = ext4_new_inode_start_handle(dir, mode,
+       inode = ext4_new_inode_start_handle(mnt_userns, dir, mode,
                                            NULL, 0, NULL,
                                            EXT4_HT_DIR,
                        EXT4_MAXQUOTAS_INIT_BLOCKS(dir->i_sb) +
@@ -2792,7 +2792,7 @@ static int ext4_mkdir(struct user_namespace *mnt_userns, struct inode *dir,
        credits = (EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
                   EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3);
 retry:
-       inode = ext4_new_inode_start_handle(dir, S_IFDIR | mode,
+       inode = ext4_new_inode_start_handle(mnt_userns, dir, S_IFDIR | mode,
                                            &dentry->d_name,
                                            0, NULL, EXT4_HT_DIR, credits);
        handle = ext4_journal_current_handle();
@@ -3335,7 +3335,7 @@ static int ext4_symlink(struct user_namespace *mnt_userns, struct inode *dir,
                          EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3;
        }
 
-       inode = ext4_new_inode_start_handle(dir, S_IFLNK|S_IRWXUGO,
+       inode = ext4_new_inode_start_handle(mnt_userns, dir, S_IFLNK|S_IRWXUGO,
                                            &dentry->d_name, 0, NULL,
                                            EXT4_HT_DIR, credits);
        handle = ext4_journal_current_handle();
@@ -3664,7 +3664,8 @@ static void ext4_update_dir_count(handle_t *handle, struct ext4_renament *ent)
        }
 }
 
-static struct inode *ext4_whiteout_for_rename(struct ext4_renament *ent,
+static struct inode *ext4_whiteout_for_rename(struct user_namespace *mnt_userns,
+                                             struct ext4_renament *ent,
                                              int credits, handle_t **h)
 {
        struct inode *wh;
@@ -3678,7 +3679,8 @@ static struct inode *ext4_whiteout_for_rename(struct ext4_renament *ent,
        credits += (EXT4_MAXQUOTAS_TRANS_BLOCKS(ent->dir->i_sb) +
                    EXT4_XATTR_TRANS_BLOCKS + 4);
 retry:
-       wh = ext4_new_inode_start_handle(ent->dir, S_IFCHR | WHITEOUT_MODE,
+       wh = ext4_new_inode_start_handle(mnt_userns, ent->dir,
+                                        S_IFCHR | WHITEOUT_MODE,
                                         &ent->dentry->d_name, 0, NULL,
                                         EXT4_HT_DIR, credits);
 
@@ -3705,9 +3707,9 @@ retry:
  * while new_{dentry,inode) refers to the destination dentry/inode
  * This comes from rename(const char *oldpath, const char *newpath)
  */
-static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
-                      struct inode *new_dir, struct dentry *new_dentry,
-                      unsigned int flags)
+static int ext4_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
+                      struct dentry *old_dentry, struct inode *new_dir,
+                      struct dentry *new_dentry, unsigned int flags)
 {
        handle_t *handle = NULL;
        struct ext4_renament old = {
@@ -3791,7 +3793,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
                        goto end_rename;
                }
        } else {
-               whiteout = ext4_whiteout_for_rename(&old, credits, &handle);
+               whiteout = ext4_whiteout_for_rename(mnt_userns, &old, credits, &handle);
                if (IS_ERR(whiteout)) {
                        retval = PTR_ERR(whiteout);
                        whiteout = NULL;
@@ -4110,7 +4112,7 @@ static int ext4_rename2(struct user_namespace *mnt_userns,
                                         new_dir, new_dentry);
        }
 
-       return ext4_rename(old_dir, old_dentry, new_dir, new_dentry, flags);
+       return ext4_rename(mnt_userns, old_dir, old_dentry, new_dir, new_dentry, flags);
 }
 
 /*

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9a6f987..a77fbb7 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -6654,7 +6654,7 @@ static struct file_system_type ext4_fs_type = {
        .name           = "ext4",
        .mount          = ext4_mount,
        .kill_sb        = kill_block_super,
-       .fs_flags       = FS_REQUIRES_DEV,
+       .fs_flags       = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
 };
 MODULE_ALIAS_FS("ext4");