[PATCH] arch:powerpc simple_write_to_buffer return check

[PATCH] arch:powerpc simple_write_to_buffer return check

[Mayank Suman]

Signed-off-by: Mayank Suman <mayanksuman@live.com>
---
 arch/powerpc/kernel/eeh.c                    | 8 ++++----
 arch/powerpc/platforms/powernv/eeh-powernv.c | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
index 813713c9120c..2dbe1558a71f 100644
--- a/arch/powerpc/kernel/eeh.c
+++ b/arch/powerpc/kernel/eeh.c
@@ -1628,8 +1628,8 @@ static ssize_t eeh_force_recover_write(struct file *filp,
 	char buf[20];
 	int ret;
 
-	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
-	if (!ret)
+	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
+	if (ret <= 0)
 		return -EFAULT;
 
 	/*
@@ -1696,7 +1696,7 @@ static ssize_t eeh_dev_check_write(struct file *filp,
 
 	memset(buf, 0, sizeof(buf));
 	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
-	if (!ret)
+	if (ret <= 0)
 		return -EFAULT;
 
 	ret = sscanf(buf, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
@@ -1836,7 +1836,7 @@ static ssize_t eeh_dev_break_write(struct file *filp,
 
 	memset(buf, 0, sizeof(buf));
 	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
-	if (!ret)
+	if (ret <= 0)
 		return -EFAULT;
 
 	ret = sscanf(buf, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c b/arch/powerpc/platforms/powernv/eeh-powernv.c
index 89e22c460ebf..36ed2b8f7375 100644
--- a/arch/powerpc/platforms/powernv/eeh-powernv.c
+++ b/arch/powerpc/platforms/powernv/eeh-powernv.c
@@ -76,8 +76,8 @@ static ssize_t pnv_eeh_ei_write(struct file *filp,
 		return -ENXIO;
 
 	/* Copy over argument buffer */
-	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
-	if (!ret)
+	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
+	if (ret <= 0)
 		return -EFAULT;
 
 	/* Retrieve parameters */
-- 
2.30.0

Re: [PATCH] arch:powerpc simple_write_to_buffer return check

[Oliver O'Halloran]

On Fri, Feb 5, 2021 at 5:17 AM Mayank Suman <mayanksuman@live.com> wrote:
>
> Signed-off-by: Mayank Suman <mayanksuman@live.com>

commit messages aren't optional

> ---
>  arch/powerpc/kernel/eeh.c                    | 8 ++++----
>  arch/powerpc/platforms/powernv/eeh-powernv.c | 4 ++--
>  2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
> index 813713c9120c..2dbe1558a71f 100644
> --- a/arch/powerpc/kernel/eeh.c
> +++ b/arch/powerpc/kernel/eeh.c
> @@ -1628,8 +1628,8 @@ static ssize_t eeh_force_recover_write(struct file *filp,
>         char buf[20];
>         int ret;
>
> -       ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
> -       if (!ret)
> +       ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);

We should probably be zeroing the buffer. Reading to sizeof(buf) - 1
is done in a few places to guarantee that the string is nul
terminated, but without the preceeding memset() that isn't actually
guaranteed.

> +       if (ret <= 0)
>                 return -EFAULT;

EFAULT is supposed to be returned when the user supplies a buffer to
write(2) which is outside their address space. I figured letting the
sscanf() in the next step fail if the user passes writes a zero-length
buffer and returning EINVAL made more sense. That said, the exact
semantics around zero length writes are pretty handwavy so I guess
this isn't wrong, but I don't think it's better either.

>         /*
> @@ -1696,7 +1696,7 @@ static ssize_t eeh_dev_check_write(struct file *filp,
>
>         memset(buf, 0, sizeof(buf));
>         ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> -       if (!ret)
> +       if (ret <= 0)
>                 return -EFAULT;
>
>         ret = sscanf(buf, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
> @@ -1836,7 +1836,7 @@ static ssize_t eeh_dev_break_write(struct file *filp,
>
>         memset(buf, 0, sizeof(buf));
>         ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> -       if (!ret)
> +       if (ret <= 0)
>                 return -EFAULT;
>
>         ret = sscanf(buf, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
> diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c b/arch/powerpc/platforms/powernv/eeh-powernv.c
> index 89e22c460ebf..36ed2b8f7375 100644
> --- a/arch/powerpc/platforms/powernv/eeh-powernv.c
> +++ b/arch/powerpc/platforms/powernv/eeh-powernv.c
> @@ -76,8 +76,8 @@ static ssize_t pnv_eeh_ei_write(struct file *filp,
>                 return -ENXIO;
>
>         /* Copy over argument buffer */
> -       ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
> -       if (!ret)
> +       ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> +       if (ret <= 0)
>                 return -EFAULT;
>
>         /* Retrieve parameters */
> --
> 2.30.0
>

Re: [PATCH] arch:powerpc simple_write_to_buffer return check

[Mayank Suman]

On 05/02/21 4:05 am, Oliver O'Halloran wrote:
> On Fri, Feb 5, 2021 at 5:17 AM Mayank Suman <mayanksuman@live.com> wrote:
>>
>> Signed-off-by: Mayank Suman <mayanksuman@live.com>
> 
> commit messages aren't optional

Sorry. I will include the commit message in PATCH v2.

> 
>> ---
>>  arch/powerpc/kernel/eeh.c                    | 8 ++++----
>>  arch/powerpc/platforms/powernv/eeh-powernv.c | 4 ++--
>>  2 files changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
>> index 813713c9120c..2dbe1558a71f 100644
>> --- a/arch/powerpc/kernel/eeh.c
>> +++ b/arch/powerpc/kernel/eeh.c
>> @@ -1628,8 +1628,8 @@ static ssize_t eeh_force_recover_write(struct file *filp,
>>         char buf[20];
>>         int ret;
>>
>> -       ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
>> -       if (!ret)
>> +       ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> 
> We should probably be zeroing the buffer. Reading to sizeof(buf) - 1
> is done in a few places to guarantee that the string is nul
> terminated, but without the preceeding memset() that isn't actually
> guaranteed.

Yes, the buffer should be zeroed out first. I have included memset() in Patch v2.

> 
>> +       if (ret <= 0)
>>                 return -EFAULT;
> 
> EFAULT is supposed to be returned when the user supplies a buffer to
> write(2) which is outside their address space. I figured letting the
> sscanf() in the next step fail if the user passes writes a zero-length
> buffer and returning EINVAL made more sense. That said, the exact
> semantics around zero length writes are pretty handwavy so I guess
> this isn't wrong, but I don't think it's better either.
> 

simple_write_to_buffer may return negative value on fail.
So, -EFAULT should be return in case of negative return value. 
The conditional (!ret) was not sufficient to catch negative return value.

Re: [PATCH] arch:powerpc simple_write_to_buffer return check

[Christophe Leroy]

Please provide some description of the change.

And please clarify the patch subject, because as far as I can see, the return is already checked 
allthough the check seams wrong.

Le 04/02/2021 à 19:16, Mayank Suman a écrit :
> Signed-off-by: Mayank Suman <mayanksuman@live.com>
> ---
>   arch/powerpc/kernel/eeh.c                    | 8 ++++----
>   arch/powerpc/platforms/powernv/eeh-powernv.c | 4 ++--
>   2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
> index 813713c9120c..2dbe1558a71f 100644
> --- a/arch/powerpc/kernel/eeh.c
> +++ b/arch/powerpc/kernel/eeh.c
> @@ -1628,8 +1628,8 @@ static ssize_t eeh_force_recover_write(struct file *filp,
>   	char buf[20];
>   	int ret;
>   
> -	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
> -	if (!ret)
> +	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> +	if (ret <= 0) >   		return -EFAULT;

Why return -EFAULT when the function has returned -EINVAL ?
And why is it -EFAULT when ret is 0 ? EFAULT means error accessing memory.

>   
>   	/*
> @@ -1696,7 +1696,7 @@ static ssize_t eeh_dev_check_write(struct file *filp,
>   
>   	memset(buf, 0, sizeof(buf));
>   	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> -	if (!ret)
> +	if (ret <= 0)
>   		return -EFAULT;
>   
>   	ret = sscanf(buf, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
> @@ -1836,7 +1836,7 @@ static ssize_t eeh_dev_break_write(struct file *filp,
>   
>   	memset(buf, 0, sizeof(buf));
>   	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> -	if (!ret)
> +	if (ret <= 0)
>   		return -EFAULT;
>   
>   	ret = sscanf(buf, "%x:%x:%x.%x", &domain, &bus, &dev, &fn);
> diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c b/arch/powerpc/platforms/powernv/eeh-powernv.c
> index 89e22c460ebf..36ed2b8f7375 100644
> --- a/arch/powerpc/platforms/powernv/eeh-powernv.c
> +++ b/arch/powerpc/platforms/powernv/eeh-powernv.c
> @@ -76,8 +76,8 @@ static ssize_t pnv_eeh_ei_write(struct file *filp,
>   		return -ENXIO;
>   
>   	/* Copy over argument buffer */
> -	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
> -	if (!ret)
> +	ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
> +	if (ret <= 0)
>   		return -EFAULT;
>   
>   	/* Retrieve parameters */
> 

Re: [PATCH] arch:powerpc simple_write_to_buffer return check

[Mayank Suman]

On 05/02/21 12:51 pm, Christophe Leroy wrote:
> Please provide some description of the change.
> 
> And please clarify the patch subject, because as far as I can see, the return is already checked allthough the check seams wrong.

This was my first patch. I will try to provide better description of changes and subject in later patches.

> Le 04/02/2021 à 19:16, Mayank Suman a écrit :
>> Signed-off-by: Mayank Suman <mayanksuman@live.com>
>> ---
>>   arch/powerpc/kernel/eeh.c                    | 8 ++++----
>>   arch/powerpc/platforms/powernv/eeh-powernv.c | 4 ++--
>>   2 files changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
>> index 813713c9120c..2dbe1558a71f 100644
>> --- a/arch/powerpc/kernel/eeh.c
>> +++ b/arch/powerpc/kernel/eeh.c
>> @@ -1628,8 +1628,8 @@ static ssize_t eeh_force_recover_write(struct file *filp,
>>       char buf[20];
>>       int ret;
>>   -    ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
>> -    if (!ret)
>> +    ret = simple_write_to_buffer(buf, sizeof(buf)-1, ppos, user_buf, count);
>> +    if (ret <= 0) >           return -EFAULT;
> 
> Why return -EFAULT when the function has returned -EINVAL ?

If -EINVAL is returned by simple_write_to_buffer, we should return -EINVAL.

> And why is it -EFAULT when ret is 0 ? EFAULT means error accessing memory.
> 

The earlier check returned EFAULT when ret is 0. Most probably, there was an assumption
that writing 0 bytes (by simple_write_to_buffer) means a fault with memory (or error accessing memory).