[PATCH v4] Add ioctls to get/set the ext4 superblock uuid.

Jeremy Bongio
2022-07-19T23:41:40Z

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>
---

Changes in v4:
Removed unused variable.

fs/ext4/ext4.h | 11 +++++++
fs/ext4/ioctl.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 87 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 75b8d81b2469..b760d669a1ca 100644
--- 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 cb01c1da0f9d..2c4c3eedfb7b 100644
--- 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,
@@ -1131,6 +1141,66 @@ 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 != 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);
@@ -1509,6 +1579,10 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
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;
}
@@ -1586,6 +1660,8 @@ 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;
--
2.37.0.170.g444d1eabd0-goog