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From: Matt Mackall on 26 Jan 2010 21:20
On Tue, 2010-01-26 at 20:44 -0500, Jeff Angielski wrote:
> Artem Bityutskiy wrote:
> > On Mon, 2010-01-25 at 23:48 -0600, Matt Mackall wrote:
> >> Hmm. I'd just as soon drop it entirely. Here's a patch. Herbert, you
> >> want to send this through your crypto tree?
> >>
> >>
> >> random: drop weird m_time/a_time manipulation
> >>
> >> No other driver does anything remotely like this that I know of except
> >> for the tty drivers, and I can't see any reason for random/urandom to do
> >> it. In fact, it's a (trivial, harmless) timing information leak. And
> >> obviously, it generates power- and flash-cycle wasting I/O, especially
> >> if combined with something like hwrngd. Also, it breaks ubifs's
> >> expectations.
> >>
> >> Signed-off-by: Matt Mackall <mpm(a)selenic.com>
> >>
> >> diff -r 29db0c391ce8 drivers/char/random.c
> >> --- a/drivers/char/random.c Sun Jan 17 11:01:16 2010 -0800
> >> +++ b/drivers/char/random.c Mon Jan 25 23:32:00 2010 -0600
> >> @@ -1051,12 +1051,6 @@
> >> /* like a named pipe */
> >> }
> >>
> >> - /*
> >> - * If we gave the user some bytes, update the access time.
> >> - */
> >> - if (count)
> >> - file_accessed(file);
> >> -
> >> return (count ? count : retval);
> >> }
> >>
> >> @@ -1116,8 +1110,6 @@
> >> if (ret)
> >> return ret;
> >>
> >> - inode->i_mtime = current_fs_time(inode->i_sb);
> >> - mark_inode_dirty(inode);
> >> return (ssize_t)count;
> >> }
> >
> > It may brake other FSes expectations, theoretically, as well.
> >
> > Anyway, I'm perfectly fine if this is removed.
> >
> > Jeff, could you please try Matt's patch and report back if you still
> > have issues or not. If no, you can use this as a temporary work-around
> > until a proper fix hits upstream or ubifs-2.6.git.
>
> Matt's patch did not compile as written. I tried to implement what I
> think he was trying to do and created this patch (it seems to match the
> guts of what inode_setattr() was looking for):
>
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 8258982..70f16c7 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1108,6 +1108,7 @@ static ssize_t random_write(struct file *file,
> const char __user *buffer,
> {
> size_t ret;
> struct inode *inode = file->f_path.dentry->d_inode;
> + struct iattr attr;
>
> ret = write_pool(&blocking_pool, buffer, count);
> if (ret)
> @@ -1116,8 +1117,12 @@ static ssize_t random_write(struct file *file,
> const char __user *buffer,
> if (ret)
> return ret;
>
> - inode->i_mtime = current_fs_time(inode->i_sb);
> - mark_inode_dirty(inode);
> + attr.ia_mtime = current_fs_time(inode->i_sb);
> + attr.ia_valid = ATTR_MTIME;
> + ret = inode_setattr(inode, &attr);
> + if (ret)
> + return ret;
> +
> return (ssize_t)count;
> }
>
> However, this patch does not fix the problem. I still see the same
> errors. Matt, is this what you were trying to do?

That doesn't look anything like my patch? And mine was test compiled.

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From: Jeff Angielski on 26 Jan 2010 22:10
Matt Mackall wrote:
> On Tue, 2010-01-26 at 20:44 -0500, Jeff Angielski wrote:
>> Artem Bityutskiy wrote:
>>> On Mon, 2010-01-25 at 23:48 -0600, Matt Mackall wrote:
>>>> Hmm. I'd just as soon drop it entirely. Here's a patch. Herbert, you
>>>> want to send this through your crypto tree?
>>>>
>>>>
>>>> random: drop weird m_time/a_time manipulation
>>>>
>>>> No other driver does anything remotely like this that I know of except
>>>> for the tty drivers, and I can't see any reason for random/urandom to do
>>>> it. In fact, it's a (trivial, harmless) timing information leak. And
>>>> obviously, it generates power- and flash-cycle wasting I/O, especially
>>>> if combined with something like hwrngd. Also, it breaks ubifs's
>>>> expectations.
>>>>
>>>> Signed-off-by: Matt Mackall <mpm(a)selenic.com>
>>>>
>>>> diff -r 29db0c391ce8 drivers/char/random.c
>>>> --- a/drivers/char/random.c Sun Jan 17 11:01:16 2010 -0800
>>>> +++ b/drivers/char/random.c Mon Jan 25 23:32:00 2010 -0600
>>>> @@ -1051,12 +1051,6 @@
>>>> /* like a named pipe */
>>>> }
>>>>
>>>> - /*
>>>> - * If we gave the user some bytes, update the access time.
>>>> - */
>>>> - if (count)
>>>> - file_accessed(file);
>>>> -
>>>> return (count ? count : retval);
>>>> }
>>>>
>>>> @@ -1116,8 +1110,6 @@
>>>> if (ret)
>>>> return ret;
>>>>
>>>> - inode->i_mtime = current_fs_time(inode->i_sb);
>>>> - mark_inode_dirty(inode);
>>>> return (ssize_t)count;
>>>> }
>>> It may brake other FSes expectations, theoretically, as well.
>>>
>>> Anyway, I'm perfectly fine if this is removed.
>>>
>>> Jeff, could you please try Matt's patch and report back if you still
>>> have issues or not. If no, you can use this as a temporary work-around
>>> until a proper fix hits upstream or ubifs-2.6.git.
>> Matt's patch did not compile as written. I tried to implement what I
>> think he was trying to do and created this patch (it seems to match the
>> guts of what inode_setattr() was looking for):
>>
>>
>> diff --git a/drivers/char/random.c b/drivers/char/random.c
>> index 8258982..70f16c7 100644
>> --- a/drivers/char/random.c
>> +++ b/drivers/char/random.c
>> @@ -1108,6 +1108,7 @@ static ssize_t random_write(struct file *file,
>> const char __user *buffer,
>> {
>> size_t ret;
>> struct inode *inode = file->f_path.dentry->d_inode;
>> + struct iattr attr;
>>
>> ret = write_pool(&blocking_pool, buffer, count);
>> if (ret)
>> @@ -1116,8 +1117,12 @@ static ssize_t random_write(struct file *file,
>> const char __user *buffer,
>> if (ret)
>> return ret;
>>
>> - inode->i_mtime = current_fs_time(inode->i_sb);
>> - mark_inode_dirty(inode);
>> + attr.ia_mtime = current_fs_time(inode->i_sb);
>> + attr.ia_valid = ATTR_MTIME;
>> + ret = inode_setattr(inode, &attr);
>> + if (ret)
>> + return ret;
>> +
>> return (ssize_t)count;
>> }
>>
>> However, this patch does not fix the problem. I still see the same
>> errors. Matt, is this what you were trying to do?
>
> That doesn't look anything like my patch? And mine was test compiled.

Ahh, you would be right. I mixed up authors. My bad. ;)

Matt's patch that removes the offending code works fine.

Artem's patch that tries to fix the offending code (and does not compile
as posted) does not work.


--
Jeff Angielski
The PTR Group
www.theptrgroup.com
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From: Artem Bityutskiy on 26 Jan 2010 23:30
On Tue, 2010-01-26 at 22:07 -0500, Jeff Angielski wrote:
> Matt Mackall wrote:
> > On Tue, 2010-01-26 at 20:44 -0500, Jeff Angielski wrote:
> >> Artem Bityutskiy wrote:
> >>> On Mon, 2010-01-25 at 23:48 -0600, Matt Mackall wrote:
> >>>> Hmm. I'd just as soon drop it entirely. Here's a patch. Herbert, you
> >>>> want to send this through your crypto tree?
> >>>>
> >>>>
> >>>> random: drop weird m_time/a_time manipulation
> >>>>
> >>>> No other driver does anything remotely like this that I know of except
> >>>> for the tty drivers, and I can't see any reason for random/urandom to do
> >>>> it. In fact, it's a (trivial, harmless) timing information leak. And
> >>>> obviously, it generates power- and flash-cycle wasting I/O, especially
> >>>> if combined with something like hwrngd. Also, it breaks ubifs's
> >>>> expectations.
> >>>>
> >>>> Signed-off-by: Matt Mackall <mpm(a)selenic.com>
> >>>>
> >>>> diff -r 29db0c391ce8 drivers/char/random.c
> >>>> --- a/drivers/char/random.c Sun Jan 17 11:01:16 2010 -0800
> >>>> +++ b/drivers/char/random.c Mon Jan 25 23:32:00 2010 -0600
> >>>> @@ -1051,12 +1051,6 @@
> >>>> /* like a named pipe */
> >>>> }
> >>>>
> >>>> - /*
> >>>> - * If we gave the user some bytes, update the access time.
> >>>> - */
> >>>> - if (count)
> >>>> - file_accessed(file);
> >>>> -
> >>>> return (count ? count : retval);
> >>>> }
> >>>>
> >>>> @@ -1116,8 +1110,6 @@
> >>>> if (ret)
> >>>> return ret;
> >>>>
> >>>> - inode->i_mtime = current_fs_time(inode->i_sb);
> >>>> - mark_inode_dirty(inode);
> >>>> return (ssize_t)count;
> >>>> }
> >>> It may brake other FSes expectations, theoretically, as well.
> >>>
> >>> Anyway, I'm perfectly fine if this is removed.
> >>>
> >>> Jeff, could you please try Matt's patch and report back if you still
> >>> have issues or not. If no, you can use this as a temporary work-around
> >>> until a proper fix hits upstream or ubifs-2.6.git.
> >> Matt's patch did not compile as written. I tried to implement what I
> >> think he was trying to do and created this patch (it seems to match the
> >> guts of what inode_setattr() was looking for):
> >>
> >>
> >> diff --git a/drivers/char/random.c b/drivers/char/random.c
> >> index 8258982..70f16c7 100644
> >> --- a/drivers/char/random.c
> >> +++ b/drivers/char/random.c
> >> @@ -1108,6 +1108,7 @@ static ssize_t random_write(struct file *file,
> >> const char __user *buffer,
> >> {
> >> size_t ret;
> >> struct inode *inode = file->f_path.dentry->d_inode;
> >> + struct iattr attr;
> >>
> >> ret = write_pool(&blocking_pool, buffer, count);
> >> if (ret)
> >> @@ -1116,8 +1117,12 @@ static ssize_t random_write(struct file *file,
> >> const char __user *buffer,
> >> if (ret)
> >> return ret;
> >>
> >> - inode->i_mtime = current_fs_time(inode->i_sb);
> >> - mark_inode_dirty(inode);
> >> + attr.ia_mtime = current_fs_time(inode->i_sb);
> >> + attr.ia_valid = ATTR_MTIME;
> >> + ret = inode_setattr(inode, &attr);
> >> + if (ret)
> >> + return ret;
> >> +
> >> return (ssize_t)count;
> >> }
> >>
> >> However, this patch does not fix the problem. I still see the same
> >> errors. Matt, is this what you were trying to do?
> >
> > That doesn't look anything like my patch? And mine was test compiled.
>
> Ahh, you would be right. I mixed up authors. My bad. ;)
>
> Matt's patch that removes the offending code works fine.
>
> Artem's patch that tries to fix the offending code (and does not compile
> as posted) does not work.

Thanks for testing. So, who would bring Matt's patch upstream then, hmm?

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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From: Matt Mackall on 27 Jan 2010 00:20
On Wed, 2010-01-27 at 06:20 +0200, Artem Bityutskiy wrote:
> On Tue, 2010-01-26 at 22:07 -0500, Jeff Angielski wrote:
> > Matt Mackall wrote:
> > > On Tue, 2010-01-26 at 20:44 -0500, Jeff Angielski wrote:
> > >> Artem Bityutskiy wrote:
> > >>> On Mon, 2010-01-25 at 23:48 -0600, Matt Mackall wrote:
> > >>>> Hmm. I'd just as soon drop it entirely. Here's a patch. Herbert, you
> > >>>> want to send this through your crypto tree?
> > >>>>
> > >>>>
> > >>>> random: drop weird m_time/a_time manipulation
> > >>>>
> > >>>> No other driver does anything remotely like this that I know of except
> > >>>> for the tty drivers, and I can't see any reason for random/urandom to do
> > >>>> it. In fact, it's a (trivial, harmless) timing information leak. And
> > >>>> obviously, it generates power- and flash-cycle wasting I/O, especially
> > >>>> if combined with something like hwrngd. Also, it breaks ubifs's
> > >>>> expectations.
> > >>>>
> > >>>> Signed-off-by: Matt Mackall <mpm(a)selenic.com>
> > >>>>
> > >>>> diff -r 29db0c391ce8 drivers/char/random.c
> > >>>> --- a/drivers/char/random.c Sun Jan 17 11:01:16 2010 -0800
> > >>>> +++ b/drivers/char/random.c Mon Jan 25 23:32:00 2010 -0600
> > >>>> @@ -1051,12 +1051,6 @@
> > >>>> /* like a named pipe */
> > >>>> }
> > >>>>
> > >>>> - /*
> > >>>> - * If we gave the user some bytes, update the access time.
> > >>>> - */
> > >>>> - if (count)
> > >>>> - file_accessed(file);
> > >>>> -
> > >>>> return (count ? count : retval);
> > >>>> }
> > >>>>
> > >>>> @@ -1116,8 +1110,6 @@
> > >>>> if (ret)
> > >>>> return ret;
> > >>>>
> > >>>> - inode->i_mtime = current_fs_time(inode->i_sb);
> > >>>> - mark_inode_dirty(inode);
> > >>>> return (ssize_t)count;
> > >>>> }
> > >>> It may brake other FSes expectations, theoretically, as well.
> > >>>
> > >>> Anyway, I'm perfectly fine if this is removed.
> > >>>
> > >>> Jeff, could you please try Matt's patch and report back if you still
> > >>> have issues or not. If no, you can use this as a temporary work-around
> > >>> until a proper fix hits upstream or ubifs-2.6.git.
> > >> Matt's patch did not compile as written. I tried to implement what I
> > >> think he was trying to do and created this patch (it seems to match the
> > >> guts of what inode_setattr() was looking for):
> > >>
> > >>
> > >> diff --git a/drivers/char/random.c b/drivers/char/random.c
> > >> index 8258982..70f16c7 100644
> > >> --- a/drivers/char/random.c
> > >> +++ b/drivers/char/random.c
> > >> @@ -1108,6 +1108,7 @@ static ssize_t random_write(struct file *file,
> > >> const char __user *buffer,
> > >> {
> > >> size_t ret;
> > >> struct inode *inode = file->f_path.dentry->d_inode;
> > >> + struct iattr attr;
> > >>
> > >> ret = write_pool(&blocking_pool, buffer, count);
> > >> if (ret)
> > >> @@ -1116,8 +1117,12 @@ static ssize_t random_write(struct file *file,
> > >> const char __user *buffer,
> > >> if (ret)
> > >> return ret;
> > >>
> > >> - inode->i_mtime = current_fs_time(inode->i_sb);
> > >> - mark_inode_dirty(inode);
> > >> + attr.ia_mtime = current_fs_time(inode->i_sb);
> > >> + attr.ia_valid = ATTR_MTIME;
> > >> + ret = inode_setattr(inode, &attr);
> > >> + if (ret)
> > >> + return ret;
> > >> +
> > >> return (ssize_t)count;
> > >> }
> > >>
> > >> However, this patch does not fix the problem. I still see the same
> > >> errors. Matt, is this what you were trying to do?
> > >
> > > That doesn't look anything like my patch? And mine was test compiled.
> >
> > Ahh, you would be right. I mixed up authors. My bad. ;)
> >
> > Matt's patch that removes the offending code works fine.
> >
> > Artem's patch that tries to fix the offending code (and does not compile
> > as posted) does not work.
>
> Thanks for testing. So, who would bring Matt's patch upstream then, hmm?
>

I think Herbert's tree is the best path, but if he doesn't chime in,
I'll send it through Andrew.

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From: Herbert Xu on 29 Jan 2010 03:50
On Mon, Jan 25, 2010 at 11:48:48PM -0600, Matt Mackall wrote:
>
> random: drop weird m_time/a_time manipulation
>
> No other driver does anything remotely like this that I know of except
> for the tty drivers, and I can't see any reason for random/urandom to do
> it. In fact, it's a (trivial, harmless) timing information leak. And
> obviously, it generates power- and flash-cycle wasting I/O, especially
> if combined with something like hwrngd. Also, it breaks ubifs's
> expectations.
>
> Signed-off-by: Matt Mackall <mpm(a)selenic.com>

Thanks Matt, I'll add this to crypto-2.6 and then stable.
--
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Email: Herbert Xu ~{PmV>HI~} <herbert(a)gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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