[PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Konstantin Khlebnikov]

Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
byte at a time. Script gets 'i' instead of 'idle' when reads current action
from /sys/block/$dev/md/sync_action and as a result does nothing.

This patch adds trivial implementation of partial read: generate whole
string and move required part into buffer head.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
Cc: Stable <stable@vger.kernel.org> # v3.19+
---
 fs/sysfs/file.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index f35523d4fa3a..b803213d1307 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
 	 * If buf != of->prealloc_buf, we don't know how
 	 * large it is, so cannot safely pass it to ->show
 	 */
-	if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
+	if (WARN_ON_ONCE(buf != of->prealloc_buf))
 		return 0;
 	len = ops->show(kobj, of->kn->priv, buf);
+	if (pos) {
+		if (len <= pos)
+			return 0;
+		len -= pos;
+		memmove(buf, buf + pos, len);
+	}
 	return min(count, len);
 }
 

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Tejun Heo]

On Wed, Jun 22, 2016 at 09:42:16PM +0300, Konstantin Khlebnikov wrote:
> Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
> zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
> in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
> byte at a time. Script gets 'i' instead of 'idle' when reads current action
> from /sys/block/$dev/md/sync_action and as a result does nothing.
> 
> This patch adds trivial implementation of partial read: generate whole
> string and move required part into buffer head.
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
> Cc: Stable <stable@vger.kernel.org> # v3.19+

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Konstantin Khlebnikov]

Bump

On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov
<khlebnikov@yandex-team.ru> wrote:
> Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
> zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
> in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
> byte at a time. Script gets 'i' instead of 'idle' when reads current action
> from /sys/block/$dev/md/sync_action and as a result does nothing.
>
> This patch adds trivial implementation of partial read: generate whole
> string and move required part into buffer head.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
> Cc: Stable <stable@vger.kernel.org> # v3.19+
> ---
>  fs/sysfs/file.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index f35523d4fa3a..b803213d1307 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
>          * If buf != of->prealloc_buf, we don't know how
>          * large it is, so cannot safely pass it to ->show
>          */
> -       if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
> +       if (WARN_ON_ONCE(buf != of->prealloc_buf))
>                 return 0;
>         len = ops->show(kobj, of->kn->priv, buf);
> +       if (pos) {
> +               if (len <= pos)
> +                       return 0;
> +               len -= pos;
> +               memmove(buf, buf + pos, len);
> +       }
>         return min(count, len);
>  }
>
>

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Greg Kroah-Hartman]

On Mon, Sep 05, 2016 at 04:25:48PM +0300, Konstantin Khlebnikov wrote:
> Bump

Huh?

> On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov
> <khlebnikov@yandex-team.ru> wrote:
> > Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
> > zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
> > in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
> > byte at a time. Script gets 'i' instead of 'idle' when reads current action
> > from /sys/block/$dev/md/sync_action and as a result does nothing.
> >
> > This patch adds trivial implementation of partial read: generate whole
> > string and move required part into buffer head.
> >
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
> > Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
> > Cc: Stable <stable@vger.kernel.org> # v3.19+
> > ---
> >  fs/sysfs/file.c |    8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> > index f35523d4fa3a..b803213d1307 100644
> > --- a/fs/sysfs/file.c
> > +++ b/fs/sysfs/file.c
> > @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
> >          * If buf != of->prealloc_buf, we don't know how
> >          * large it is, so cannot safely pass it to ->show
> >          */
> > -       if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
> > +       if (WARN_ON_ONCE(buf != of->prealloc_buf))
> >                 return 0;
> >         len = ops->show(kobj, of->kn->priv, buf);
> > +       if (pos) {
> > +               if (len <= pos)
> > +                       return 0;
> > +               len -= pos;
> > +               memmove(buf, buf + pos, len);
> > +       }
> >         return min(count, len);
> >  }

I don't have this in any queue of mine, so I don't understand what you
are asking about.

totally confused,

greg k-h

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Konstantin Khlebnikov]

On 05.09.2016 16:46, Greg Kroah-Hartman wrote:
> On Mon, Sep 05, 2016 at 04:25:48PM +0300, Konstantin Khlebnikov wrote:
>> Bump
>
> Huh?
>
>> On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov
>> <khlebnikov@yandex-team.ru> wrote:
>>> Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
>>> zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
>>> in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
>>> byte at a time. Script gets 'i' instead of 'idle' when reads current action
>>> from /sys/block/$dev/md/sync_action and as a result does nothing.
>>>
>>> This patch adds trivial implementation of partial read: generate whole
>>> string and move required part into buffer head.
>>>
>>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>>> Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
>>> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
>>> Cc: Stable <stable@vger.kernel.org> # v3.19+
>>> ---
>>>  fs/sysfs/file.c |    8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
>>> index f35523d4fa3a..b803213d1307 100644
>>> --- a/fs/sysfs/file.c
>>> +++ b/fs/sysfs/file.c
>>> @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
>>>          * If buf != of->prealloc_buf, we don't know how
>>>          * large it is, so cannot safely pass it to ->show
>>>          */
>>> -       if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
>>> +       if (WARN_ON_ONCE(buf != of->prealloc_buf))
>>>                 return 0;
>>>         len = ops->show(kobj, of->kn->priv, buf);
>>> +       if (pos) {
>>> +               if (len <= pos)
>>> +                       return 0;
>>> +               len -= pos;
>>> +               memmove(buf, buf + pos, len);
>>> +       }
>>>         return min(count, len);
>>>  }
>
> I don't have this in any queue of mine, so I don't understand what you
> are asking about.
>
> totally confused,
>

Well.. One user poked me about this bug.

Patch was
Acked-by: Tejun Heo <tj@kernel.org>

get_maintainer.pl points to you but probably this more VFS problem. so... this time I've added Al into CC
Should I resend patch once again, or this very trivial but pretty dangerous problem could be solved without this?

IIRR this breaks automatic recheck of MD RAIDs for all debian-based systems

-- 
Konstantin

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Greg Kroah-Hartman]

On Mon, Sep 05, 2016 at 03:46:28PM +0200, Greg Kroah-Hartman wrote:
> On Mon, Sep 05, 2016 at 04:25:48PM +0300, Konstantin Khlebnikov wrote:
> > Bump
> 
> Huh?
> 
> > On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov
> > <khlebnikov@yandex-team.ru> wrote:
> > > Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
> > > zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
> > > in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
> > > byte at a time. Script gets 'i' instead of 'idle' when reads current action
> > > from /sys/block/$dev/md/sync_action and as a result does nothing.
> > >
> > > This patch adds trivial implementation of partial read: generate whole
> > > string and move required part into buffer head.
> > >
> > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > > Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
> > > Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
> > > Cc: Stable <stable@vger.kernel.org> # v3.19+
> > > ---
> > >  fs/sysfs/file.c |    8 +++++++-
> > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> > > index f35523d4fa3a..b803213d1307 100644
> > > --- a/fs/sysfs/file.c
> > > +++ b/fs/sysfs/file.c
> > > @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
> > >          * If buf != of->prealloc_buf, we don't know how
> > >          * large it is, so cannot safely pass it to ->show
> > >          */
> > > -       if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
> > > +       if (WARN_ON_ONCE(buf != of->prealloc_buf))
> > >                 return 0;
> > >         len = ops->show(kobj, of->kn->priv, buf);
> > > +       if (pos) {
> > > +               if (len <= pos)
> > > +                       return 0;
> > > +               len -= pos;
> > > +               memmove(buf, buf + pos, len);
> > > +       }
> > >         return min(count, len);
> > >  }
> 
> I don't have this in any queue of mine, so I don't understand what you
> are asking about.
> 
> totally confused,

Wait, this is already in Linus's tree, what are you asking for here?

still confused,

greg k-h

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Greg Kroah-Hartman]

On Mon, Sep 05, 2016 at 05:02:43PM +0300, Konstantin Khlebnikov wrote:
> On 05.09.2016 16:46, Greg Kroah-Hartman wrote:
> > On Mon, Sep 05, 2016 at 04:25:48PM +0300, Konstantin Khlebnikov wrote:
> > > Bump
> > 
> > Huh?
> > 
> > > On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov
> > > <khlebnikov@yandex-team.ru> wrote:
> > > > Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
> > > > zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
> > > > in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
> > > > byte at a time. Script gets 'i' instead of 'idle' when reads current action
> > > > from /sys/block/$dev/md/sync_action and as a result does nothing.
> > > > 
> > > > This patch adds trivial implementation of partial read: generate whole
> > > > string and move required part into buffer head.
> > > > 
> > > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > > > Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
> > > > Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
> > > > Cc: Stable <stable@vger.kernel.org> # v3.19+
> > > > ---
> > > >  fs/sysfs/file.c |    8 +++++++-
> > > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> > > > index f35523d4fa3a..b803213d1307 100644
> > > > --- a/fs/sysfs/file.c
> > > > +++ b/fs/sysfs/file.c
> > > > @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
> > > >          * If buf != of->prealloc_buf, we don't know how
> > > >          * large it is, so cannot safely pass it to ->show
> > > >          */
> > > > -       if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
> > > > +       if (WARN_ON_ONCE(buf != of->prealloc_buf))
> > > >                 return 0;
> > > >         len = ops->show(kobj, of->kn->priv, buf);
> > > > +       if (pos) {
> > > > +               if (len <= pos)
> > > > +                       return 0;
> > > > +               len -= pos;
> > > > +               memmove(buf, buf + pos, len);
> > > > +       }
> > > >         return min(count, len);
> > > >  }
> > 
> > I don't have this in any queue of mine, so I don't understand what you
> > are asking about.
> > 
> > totally confused,
> > 
> 
> Well.. One user poked me about this bug.

As I just mentioned, this is in 4.8-rc5, and will show up in a stable
release "soon".  So I don't understand what else we can do here :)

thanks,

greg k-h

Re: [PATCH] sysfs: correctly handle read offset on PREALLOC attrs

[Konstantin Khlebnikov]

On Mon, Sep 5, 2016 at 5:13 PM, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> On Mon, Sep 05, 2016 at 03:46:28PM +0200, Greg Kroah-Hartman wrote:
>> On Mon, Sep 05, 2016 at 04:25:48PM +0300, Konstantin Khlebnikov wrote:
>> > Bump
>>
>> Huh?
>>
>> > On Wed, Jun 22, 2016 at 9:42 PM, Konstantin Khlebnikov
>> > <khlebnikov@yandex-team.ru> wrote:
>> > > Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns
>> > > zero bytes for non-zero offset. This breaks script checkarray in mdadm tool
>> > > in debian where /bin/sh is 'dash' because its builtin 'read' reads only one
>> > > byte at a time. Script gets 'i' instead of 'idle' when reads current action
>> > > from /sys/block/$dev/md/sync_action and as a result does nothing.
>> > >
>> > > This patch adds trivial implementation of partial read: generate whole
>> > > string and move required part into buffer head.
>> > >
>> > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>> > > Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.")
>> > > Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950
>> > > Cc: Stable <stable@vger.kernel.org> # v3.19+
>> > > ---
>> > >  fs/sysfs/file.c |    8 +++++++-
>> > >  1 file changed, 7 insertions(+), 1 deletion(-)
>> > >
>> > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
>> > > index f35523d4fa3a..b803213d1307 100644
>> > > --- a/fs/sysfs/file.c
>> > > +++ b/fs/sysfs/file.c
>> > > @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
>> > >          * If buf != of->prealloc_buf, we don't know how
>> > >          * large it is, so cannot safely pass it to ->show
>> > >          */
>> > > -       if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
>> > > +       if (WARN_ON_ONCE(buf != of->prealloc_buf))
>> > >                 return 0;
>> > >         len = ops->show(kobj, of->kn->priv, buf);
>> > > +       if (pos) {
>> > > +               if (len <= pos)
>> > > +                       return 0;
>> > > +               len -= pos;
>> > > +               memmove(buf, buf + pos, len);
>> > > +       }
>> > >         return min(count, len);
>> > >  }
>>
>> I don't have this in any queue of mine, so I don't understand what you
>> are asking about.
>>
>> totally confused,
>
> Wait, this is already in Linus's tree, what are you asking for here?
>
> still confused,
>

Huh. Sorry. Haven't done git pull before checking - it only in lastest v4.8-rc5