ext4: add ioctls to get/set the ext4 superblock uuid

This fixes a race between changing the ext4 superblock uuid and operations
like mounting, resizing, changing features, etc.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jeremy Bongio <bongiojp@gmail.com>
Link: https://lore.kernel.org/r/20220721224422.438351-1-bongiojp@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 310e976..349c9a1 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -724,6 +724,8 @@ enum {
 #define EXT4_IOC_GETSTATE              _IOW('f', 41, __u32)
 #define EXT4_IOC_GET_ES_CACHE          _IOWR('f', 42, struct fiemap)
 #define EXT4_IOC_CHECKPOINT            _IOW('f', 43, __u32)
+#define EXT4_IOC_GETFSUUID             _IOR('f', 44, struct fsuuid)
+#define EXT4_IOC_SETFSUUID             _IOW('f', 44, struct fsuuid)
 
 #define EXT4_IOC_SHUTDOWN _IOR ('X', 125, __u32)
 
@@ -753,6 +755,15 @@ enum {
                                                EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT | \
                                                EXT4_IOC_CHECKPOINT_FLAG_DRY_RUN)
 
+/*
+ * Structure for EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID
+ */
+struct fsuuid {
+       __u32       fsu_len;
+       __u32       fsu_flags;
+       __u8        fsu_uuid[];
+};
+
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /*
  * ioctl commands in 32 bit emulation

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 1702c57..3cf3ec4 100644 (file)
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -20,6 +20,7 @@
 #include <linux/delay.h>
 #include <linux/iversion.h>
 #include <linux/fileattr.h>
+#include <linux/uuid.h>
 #include "ext4_jbd2.h"
 #include "ext4.h"
 #include <linux/fsmap.h>
@@ -41,6 +42,15 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
        memcpy(es->s_volume_name, (char *)arg, EXT4_LABEL_MAX);
 }
 
+/*
+ * Superblock modification callback function for changing file system
+ * UUID.
+ */
+static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
+{
+       memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
+}
+
 static
 int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
                           ext4_update_sb_callback func,
@@ -1133,6 +1143,73 @@ static int ext4_ioctl_getlabel(struct ext4_sb_info *sbi, char __user *user_label
        return 0;
 }
 
+static int ext4_ioctl_getuuid(struct ext4_sb_info *sbi,
+                       struct fsuuid __user *ufsuuid)
+{
+       struct fsuuid fsuuid;
+       __u8 uuid[UUID_SIZE];
+
+       if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
+               return -EFAULT;
+
+       if (fsuuid.fsu_len == 0) {
+               fsuuid.fsu_len = UUID_SIZE;
+               if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid.fsu_len)))
+                       return -EFAULT;
+               return -EINVAL;
+       }
+
+       if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)
+               return -EINVAL;
+
+       lock_buffer(sbi->s_sbh);
+       memcpy(uuid, sbi->s_es->s_uuid, UUID_SIZE);
+       unlock_buffer(sbi->s_sbh);
+
+       if (copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
+               return -EFAULT;
+       return 0;
+}
+
+static int ext4_ioctl_setuuid(struct file *filp,
+                       const struct fsuuid __user *ufsuuid)
+{
+       int ret = 0;
+       struct super_block *sb = file_inode(filp)->i_sb;
+       struct fsuuid fsuuid;
+       __u8 uuid[UUID_SIZE];
+
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
+       /*
+        * If any checksums (group descriptors or metadata) are being used
+        * then the checksum seed feature is required to change the UUID.
+        */
+       if (((ext4_has_feature_gdt_csum(sb) || ext4_has_metadata_csum(sb))
+                       && !ext4_has_feature_csum_seed(sb))
+               || ext4_has_feature_stable_inodes(sb))
+               return -EOPNOTSUPP;
+
+       if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
+               return -EFAULT;
+
+       if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)
+               return -EINVAL;
+
+       if (copy_from_user(uuid, &ufsuuid->fsu_uuid[0], UUID_SIZE))
+               return -EFAULT;
+
+       ret = mnt_want_write_file(filp);
+       if (ret)
+               return ret;
+
+       ret = ext4_update_superblocks_fn(sb, ext4_sb_setuuid, &uuid);
+       mnt_drop_write_file(filp);
+
+       return ret;
+}
+
 static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
        struct inode *inode = file_inode(filp);
@@ -1515,6 +1592,10 @@ resizefs_out:
                return ext4_ioctl_setlabel(filp,
                                           (const void __user *)arg);
 
+       case EXT4_IOC_GETFSUUID:
+               return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
+       case EXT4_IOC_SETFSUUID:
+               return ext4_ioctl_setuuid(filp, (const void __user *)arg);
        default:
                return -ENOTTY;
        }
@@ -1592,6 +1673,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
        case EXT4_IOC_CHECKPOINT:
        case FS_IOC_GETFSLABEL:
        case FS_IOC_SETFSLABEL:
+       case EXT4_IOC_GETFSUUID:
+       case EXT4_IOC_SETFSUUID:
                break;
        default:
                return -ENOIOCTLCMD;