On Tue, Jul 5, 2022 at 10:07 AM Darrick J. Wong <djwong@xxxxxxxxxx> wrote: > > On Fri, Jul 01, 2022 at 01:11:23PM -0700, Jeremy Bongio wrote: > > This fixes a race between changing the ext4 superblock uuid and operations > > like mounting, resizing, changing features, etc. > > > > Reviewed-by: Theodore Ts'o <tytso@xxxxxxx> > > Signed-off-by: Jeremy Bongio <bongiojp@xxxxxxxxx> > > --- > > fs/ext4/ext4.h | 13 ++++++++ > > fs/ext4/ioctl.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++ > > 2 files changed, 96 insertions(+) > > > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > > index 75b8d81b2469..0cf960cb591e 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 +755,17 @@ enum { > > EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT | \ > > EXT4_IOC_CHECKPOINT_FLAG_DRY_RUN) > > > > +/* > > + * Structure for EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID > > + */ > > +struct fsuuid { > > + __u32 fu_len; > > + __u32 fu_flags; > > + __u8 __user fu_uuid[]; > > __user is unnecessary here -- it applies to pointers, not to struct > members. > > > +}; > > + > > +#define EXT4_IOC_SETFSUUID_FLAG_BLOCKING 0x1 > > What does this do? > > (Better yet, can you please write a manpage describing these new > ioctls?) Good idea. I'll write a manpage as if it were being converted to a general ioctl and not specific to ext4. > > > + > > #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..75069afc16ae 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 +1141,73 @@ 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) > > +{ > > + int ret = 0; > > + __u8 uuid[UUID_SIZE]; > > Save some stack space and copy sbi->s_es->s_uuid into fsuuid.fu_uuid, > and then copy_to_user from the kernel stack object out to userspace's > object. I can't copy sbi->s_es->s_uuid into fsuuid.fu_uuid since fu_uuid is a VLA (size 0 array). Are you suggesting I copy_to_user() from sbi->s_es->s_uuid into ufsuuid within the locked region? > > > + struct fsuuid fsuuid; > > + > > + if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid))) > > + return -EFAULT; > > + > > + if (fsuuid.fu_len != UUID_SIZE) > > + return -EINVAL; > > This function needs to check that fsuuid.fu_flags doesn't contain any > unknown bitflags. > > > + > > + lock_buffer(sbi->s_sbh); > > + memcpy(uuid, sbi->s_es->s_uuid, UUID_SIZE); > > + unlock_buffer(sbi->s_sbh); > > + > > + if (copy_to_user(&ufsuuid->fu_uuid[0], uuid, UUID_SIZE)) > > + ret = -EFAULT; > > + return ret; > > if (copy_to_user(...)) > 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.fu_len != UUID_SIZE) > > + return -EINVAL; > > This function needs to check that fsuuid.fu_flags doesn't contain any > unknown bits. > > > + > > + if (copy_from_user(uuid, &ufsuuid->fu_uuid[0], UUID_SIZE)) > > + return -EFAULT; > > + > > + ret = mnt_want_write_file(filp); > > + if (ret) > > + return ret; > > + > > + do { > > + if (ret == -EBUSY) > > + msleep(1000); > > + ret = ext4_update_superblocks_fn(sb, ext4_sb_setuuid, &uuid); > > + } while (ret == -EBUSY && > > + fsuuid.fu_flags & EXT4_IOC_SETFSUUID_FLAG_BLOCKING); > > So... I guess by default, userspace gets NOWAIT mode? That's a little > strange, usually kernel convention is blocking mode by default, with > nowait selectable via function flags. > > Also, what's the intended use case here? Why would we want to set a > uuid but only if the superblock(s) aren't busy? When an ext4 filesystem is being resized, which could potentially take a long time, ext4_update_superblocks_fn() will return -EBUSY. In that case we can either sleep and retry, or return EBUSY to userspace. However, for my use case, I only care about the blocking case. I'll remove the flag since the default mode will be blocking. > > --D > > > + > > + 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 +1586,10 @@ 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 +1667,8 @@ 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.rc0.161.g10f37bed90-goog > >