[PATCH] fs/nsfs.c: fix ioctl support of compat processes

[PATCH] fs/nsfs.c: fix ioctl support of compat processes

[Dmitry V. Levin]

According to Documentation/driver-api/ioctl.rst, in order to support
32-bit user space running on a 64-bit kernel, each subsystem or driver
that implements an ioctl callback handler must also implement the
corresponding compat_ioctl handler.  The compat_ptr_ioctl() helper can
be used in place of a custom compat_ioctl file operation for drivers
that only take arguments that are pointers to compatible data
structures.

In case of NS_* ioctls only NS_GET_OWNER_UID accepts an argument, and
this argument is a pointer to uid_t type, which is universally defined
to __kernel_uid32_t.

This change fixes compat strace --pidns-translation.

Note: when backporting this patch to stable kernels, commit
"compat_ioctl: add compat_ptr_ioctl()" is needed as well.

Reported-by: Ákos Uzonyi <uzonyi.akos@gmail.com>
Fixes: 6786741dbf99 ("nsfs: add ioctl to get an owning user namespace for ns file descriptor")
Cc: stable@vger.kernel.org # v4.9+
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
---
 fs/nsfs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 800c1d0eb0d0..a00236bffa2c 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -21,6 +21,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
 static const struct file_operations ns_file_operations = {
 	.llseek		= no_llseek,
 	.unlocked_ioctl = ns_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
 };
 
 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)

-- 
ldv

Re: [PATCH] fs/nsfs.c: fix ioctl support of compat processes

[Arnd Bergmann]

On Fri, Jul 24, 2020 at 2:12 AM Dmitry V. Levin <ldv@altlinux.org> wrote:
>
> According to Documentation/driver-api/ioctl.rst, in order to support
> 32-bit user space running on a 64-bit kernel, each subsystem or driver
> that implements an ioctl callback handler must also implement the
> corresponding compat_ioctl handler.  The compat_ptr_ioctl() helper can
> be used in place of a custom compat_ioctl file operation for drivers
> that only take arguments that are pointers to compatible data
> structures.
>
> In case of NS_* ioctls only NS_GET_OWNER_UID accepts an argument, and
> this argument is a pointer to uid_t type, which is universally defined
> to __kernel_uid32_t.

This is potentially dangerous to rely on, as there are two parts that
are mismatched:

- user space does not see the kernel's uid_t definition, but has its own,
  which may be either the 16-bit or the 32-bit type. 32-bit uid_t was
  introduced with linux-2.3.39 in back in 2000. glibc was already
  using 32-bit uid_t at the time in user space, but uclibc only changed
  in 2003, and others may have been even later.

- the ioctl command number is defined (incorrectly) as if there was no
  argument, so if there is any user space that happens to be built with
  a 16-bit uid_t, this does not get caught.

       Arnd

> Reported-by: Ákos Uzonyi <uzonyi.akos@gmail.com>
> Fixes: 6786741dbf99 ("nsfs: add ioctl to get an owning user namespace for ns file descriptor")
> Cc: stable@vger.kernel.org # v4.9+
> Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
> ---
>  fs/nsfs.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/nsfs.c b/fs/nsfs.c
> index 800c1d0eb0d0..a00236bffa2c 100644
> --- a/fs/nsfs.c
> +++ b/fs/nsfs.c
> @@ -21,6 +21,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
>  static const struct file_operations ns_file_operations = {
>         .llseek         = no_llseek,
>         .unlocked_ioctl = ns_ioctl,
> +       .compat_ioctl   = compat_ptr_ioctl,
>  };
>
>  static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)

Re: [PATCH] fs/nsfs.c: fix ioctl support of compat processes

[Dmitry V. Levin]

On Fri, Jul 24, 2020 at 11:20:26AM +0200, Arnd Bergmann wrote:
> On Fri, Jul 24, 2020 at 2:12 AM Dmitry V. Levin <ldv@altlinux.org> wrote:
> >
> > According to Documentation/driver-api/ioctl.rst, in order to support
> > 32-bit user space running on a 64-bit kernel, each subsystem or driver
> > that implements an ioctl callback handler must also implement the
> > corresponding compat_ioctl handler.  The compat_ptr_ioctl() helper can
> > be used in place of a custom compat_ioctl file operation for drivers
> > that only take arguments that are pointers to compatible data
> > structures.
> >
> > In case of NS_* ioctls only NS_GET_OWNER_UID accepts an argument, and
> > this argument is a pointer to uid_t type, which is universally defined
> > to __kernel_uid32_t.
> 
> This is potentially dangerous to rely on, as there are two parts that
> are mismatched:
> 
> - user space does not see the kernel's uid_t definition, but has its own,
>   which may be either the 16-bit or the 32-bit type. 32-bit uid_t was
>   introduced with linux-2.3.39 in back in 2000. glibc was already
>   using 32-bit uid_t at the time in user space, but uclibc only changed
>   in 2003, and others may have been even later.
> 
> - the ioctl command number is defined (incorrectly) as if there was no
>   argument, so if there is any user space that happens to be built with
>   a 16-bit uid_t, this does not get caught.

Note that NS_GET_OWNER_UID is provided on 32-bit architectures, too, so
this 16-bit vs 32-bit uid_t issue was exposed to userspace long time ago
when NS_GET_OWNER_UID was introduced, and making NS_GET_OWNER_UID
available for compat processes won't make any difference, as the mismatch
is not between native and compat types, but rather between 16-bit and
32-bit uid_t types.

I agree it would be correct to define NS_GET_OWNER_UID as
_IOR(NSIO, 0x4, uid_t) instead of _IO(NSIO, 0x4), but nobody Cc'ed me
on this topic when NS_GET_OWNER_UID was discussed, and that ship has long
sailed.

> > This change fixes compat strace --pidns-translation.
> > 
> > Note: when backporting this patch to stable kernels, commit
> > "compat_ioctl: add compat_ptr_ioctl()" is needed as well.
> > 
> > Reported-by: Ákos Uzonyi <uzonyi.akos@gmail.com>
> > Fixes: 6786741dbf99 ("nsfs: add ioctl to get an owning user namespace for ns file descriptor")
> > Cc: stable@vger.kernel.org # v4.9+
> > Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
> > ---
> >  fs/nsfs.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/nsfs.c b/fs/nsfs.c
> > index 800c1d0eb0d0..a00236bffa2c 100644
> > --- a/fs/nsfs.c
> > +++ b/fs/nsfs.c
> > @@ -21,6 +21,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
> >  static const struct file_operations ns_file_operations = {
> >         .llseek         = no_llseek,
> >         .unlocked_ioctl = ns_ioctl,
> > +       .compat_ioctl   = compat_ptr_ioctl,
> >  };
> >
> >  static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)

-- 
ldv

Re: [PATCH] fs/nsfs.c: fix ioctl support of compat processes

[Eric W. Biederman]

Michael,

As the original author of NS_GET_OWNER_UID can you take a look at this?

"Dmitry V. Levin" <ldv@altlinux.org> writes:

> On Fri, Jul 24, 2020 at 11:20:26AM +0200, Arnd Bergmann wrote:
>> On Fri, Jul 24, 2020 at 2:12 AM Dmitry V. Levin <ldv@altlinux.org> wrote:
>> >
>> > According to Documentation/driver-api/ioctl.rst, in order to support
>> > 32-bit user space running on a 64-bit kernel, each subsystem or driver
>> > that implements an ioctl callback handler must also implement the
>> > corresponding compat_ioctl handler.  The compat_ptr_ioctl() helper can
>> > be used in place of a custom compat_ioctl file operation for drivers
>> > that only take arguments that are pointers to compatible data
>> > structures.
>> >
>> > In case of NS_* ioctls only NS_GET_OWNER_UID accepts an argument, and
>> > this argument is a pointer to uid_t type, which is universally defined
>> > to __kernel_uid32_t.
>> 
>> This is potentially dangerous to rely on, as there are two parts that
>> are mismatched:
>> 
>> - user space does not see the kernel's uid_t definition, but has its own,
>>   which may be either the 16-bit or the 32-bit type. 32-bit uid_t was
>>   introduced with linux-2.3.39 in back in 2000. glibc was already
>>   using 32-bit uid_t at the time in user space, but uclibc only changed
>>   in 2003, and others may have been even later.
>> 
>> - the ioctl command number is defined (incorrectly) as if there was no
>>   argument, so if there is any user space that happens to be built with
>>   a 16-bit uid_t, this does not get caught.
>
> Note that NS_GET_OWNER_UID is provided on 32-bit architectures, too, so
> this 16-bit vs 32-bit uid_t issue was exposed to userspace long time ago
> when NS_GET_OWNER_UID was introduced, and making NS_GET_OWNER_UID
> available for compat processes won't make any difference, as the mismatch
> is not between native and compat types, but rather between 16-bit and
> 32-bit uid_t types.
>
> I agree it would be correct to define NS_GET_OWNER_UID as
> _IOR(NSIO, 0x4, uid_t) instead of _IO(NSIO, 0x4), but nobody Cc'ed me
> on this topic when NS_GET_OWNER_UID was discussed, and that ship has long
> sailed.
>
>> > This change fixes compat strace --pidns-translation.
>> > 
>> > Note: when backporting this patch to stable kernels, commit
>> > "compat_ioctl: add compat_ptr_ioctl()" is needed as well.
>> > 
>> > Reported-by: Ákos Uzonyi <uzonyi.akos@gmail.com>
>> > Fixes: 6786741dbf99 ("nsfs: add ioctl to get an owning user namespace for ns file descriptor")
>> > Cc: stable@vger.kernel.org # v4.9+
>> > Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
>> > ---
>> >  fs/nsfs.c | 1 +
>> >  1 file changed, 1 insertion(+)
>> >
>> > diff --git a/fs/nsfs.c b/fs/nsfs.c
>> > index 800c1d0eb0d0..a00236bffa2c 100644
>> > --- a/fs/nsfs.c
>> > +++ b/fs/nsfs.c
>> > @@ -21,6 +21,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
>> >  static const struct file_operations ns_file_operations = {
>> >         .llseek         = no_llseek,
>> >         .unlocked_ioctl = ns_ioctl,
>> > +       .compat_ioctl   = compat_ptr_ioctl,
>> >  };
>> >
>> >  static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)

Thank you,
Eric

Re: [PATCH] fs/nsfs.c: fix ioctl support of compat processes

[Dmitry V. Levin]

Hi,

On Fri, Jul 24, 2020 at 02:31:19PM -0500, Eric W. Biederman wrote:
> Michael,
> 
> As the original author of NS_GET_OWNER_UID can you take a look at this?

This is a gentle reminder that my patch hasn't been applied,
the problem reported by Ákos Uzonyi hasn't been fixed,
and the example in ioctl_ns(2) manual page doesn't work
when e.g. it's compiled with -m32 on a 64-bit kernel.

> "Dmitry V. Levin" <ldv@altlinux.org> writes:
> > On Fri, Jul 24, 2020 at 11:20:26AM +0200, Arnd Bergmann wrote:
> >> On Fri, Jul 24, 2020 at 2:12 AM Dmitry V. Levin wrote:
> >> >
> >> > According to Documentation/driver-api/ioctl.rst, in order to support
> >> > 32-bit user space running on a 64-bit kernel, each subsystem or driver
> >> > that implements an ioctl callback handler must also implement the
> >> > corresponding compat_ioctl handler.  The compat_ptr_ioctl() helper can
> >> > be used in place of a custom compat_ioctl file operation for drivers
> >> > that only take arguments that are pointers to compatible data
> >> > structures.
> >> >
> >> > In case of NS_* ioctls only NS_GET_OWNER_UID accepts an argument, and
> >> > this argument is a pointer to uid_t type, which is universally defined
> >> > to __kernel_uid32_t.
> >> 
> >> This is potentially dangerous to rely on, as there are two parts that
> >> are mismatched:
> >> 
> >> - user space does not see the kernel's uid_t definition, but has its own,
> >>   which may be either the 16-bit or the 32-bit type. 32-bit uid_t was
> >>   introduced with linux-2.3.39 in back in 2000. glibc was already
> >>   using 32-bit uid_t at the time in user space, but uclibc only changed
> >>   in 2003, and others may have been even later.
> >> 
> >> - the ioctl command number is defined (incorrectly) as if there was no
> >>   argument, so if there is any user space that happens to be built with
> >>   a 16-bit uid_t, this does not get caught.
> >
> > Note that NS_GET_OWNER_UID is provided on 32-bit architectures, too, so
> > this 16-bit vs 32-bit uid_t issue was exposed to userspace long time ago
> > when NS_GET_OWNER_UID was introduced, and making NS_GET_OWNER_UID
> > available for compat processes won't make any difference, as the mismatch
> > is not between native and compat types, but rather between 16-bit and
> > 32-bit uid_t types.
> >
> > I agree it would be correct to define NS_GET_OWNER_UID as
> > _IOR(NSIO, 0x4, uid_t) instead of _IO(NSIO, 0x4), but nobody Cc'ed me
> > on this topic when NS_GET_OWNER_UID was discussed, and that ship has long
> > sailed.
> >
> >> > This change fixes compat strace --pidns-translation.
> >> > 
> >> > Note: when backporting this patch to stable kernels, commit
> >> > "compat_ioctl: add compat_ptr_ioctl()" is needed as well.
> >> > 
> >> > Reported-by: Ákos Uzonyi <uzonyi.akos@gmail.com>
> >> > Fixes: 6786741dbf99 ("nsfs: add ioctl to get an owning user namespace for ns file descriptor")
> >> > Cc: stable@vger.kernel.org # v4.9+
> >> > Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
> >> > ---
> >> >  fs/nsfs.c | 1 +
> >> >  1 file changed, 1 insertion(+)
> >> >
> >> > diff --git a/fs/nsfs.c b/fs/nsfs.c
> >> > index 800c1d0eb0d0..a00236bffa2c 100644
> >> > --- a/fs/nsfs.c
> >> > +++ b/fs/nsfs.c
> >> > @@ -21,6 +21,7 @@ static long ns_ioctl(struct file *filp, unsigned int ioctl,
> >> >  static const struct file_operations ns_file_operations = {
> >> >         .llseek         = no_llseek,
> >> >         .unlocked_ioctl = ns_ioctl,
> >> > +       .compat_ioctl   = compat_ptr_ioctl,
> >> >  };
> >> >
> >> >  static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
> 
> Thank you,
> Eric

-- 
ldv