This fixes a race between changing the ext4 superblock uuid and operations
like mounting, resizing, changing features, etc.
Reviewed-by: Theodore Ts'o <[email protected]>
Signed-off-by: Jeremy Bongio <[email protected]>
---
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[];
+};
+
+#define EXT4_IOC_SETFSUUID_FLAG_BLOCKING 0x1
+
#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];
+ struct fsuuid fsuuid;
+
+ if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
+ return -EFAULT;
+
+ if (fsuuid.fu_len != UUID_SIZE)
+ 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->fu_uuid[0], uuid, UUID_SIZE))
+ ret = -EFAULT;
+ return ret;
+}
+
+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;
+
+ 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);
+
+ 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
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 <[email protected]>
> Signed-off-by: Jeremy Bongio <[email protected]>
> ---
> 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?)
> +
> #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.
> + 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?
--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
>
On Tue, Jul 5, 2022 at 10:07 AM Darrick J. Wong <[email protected]> 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 <[email protected]>
> > Signed-off-by: Jeremy Bongio <[email protected]>
> > ---
> > 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
> >
On Mon, Jul 11, 2022 at 09:33:00PM -0700, Jeremy Bongio wrote:
> On Tue, Jul 5, 2022 at 10:07 AM Darrick J. Wong <[email protected]> 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 <[email protected]>
> > > Signed-off-by: Jeremy Bongio <[email protected]>
> > > ---
> > > 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.
Thank you. :)
> >
> > > +
> > > #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?
No, I'd ... forgotten my own previous suggestion, so please ignore this.
> >
> > > + 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.
<nod>
--D
>
> >
> > --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
> > >