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From: Julien Grall <julien@xen.org>
To: Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org
Cc: Julien Grall <jgrall@amazon.com>,
	Ian Jackson <iwj@xenproject.org>, Wei Liu <wl@xen.org>
Subject: Re: [PATCH] tools/xenstored: Don't assume errno will not be overwritten in lu_arch()
Date: Fri, 30 Jul 2021 16:13:07 +0100	[thread overview]
Message-ID: <bd811ae4-a355-f8fd-f61a-88ea895f5385@xen.org> (raw)
In-Reply-To: <3f3843c0-5766-b483-ce25-33fe2d4359ca@suse.com>

Hi Juergen,

On 30/07/2021 09:40, Juergen Gross wrote:
> On 29.07.21 17:23, Julien Grall wrote:
>>
>>
>> On 29/07/2021 12:06, Julien Grall wrote:
>>> From: Julien Grall <jgrall@amazon.com>
>>>
>>> At the moment, do_control_lu() will set errno to 0 before calling
>>> lu_arch() and then check errno. The expectation is nothing in lu_arch()
>>> will change the value unless there is an error.
>>>
>>> However, per errno(3), a function that succeeds is allowed to change
>>> errno. In fact, syslog() will overwrite errno if the logs are rotated
>>> at the time it is called.
>>>
>>> To prevent any further issue, errno is now always set before
>>> returning NULL.
>>>
>>> Additionally, errno is only checked when returning NULL so the client
>>> can see the error message if there is any.
>>>
>>> Reported-by: Michael Kurth <mku@amazon.com>
>>> Signed-off-by: Julien Grall <jgrall@amazon.com>
>>> ---
>>>   tools/xenstore/xenstored_control.c | 5 +++--
>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/tools/xenstore/xenstored_control.c 
>>> b/tools/xenstore/xenstored_control.c
>>> index 6b68b79faac7..6fcb42095b59 100644
>>> --- a/tools/xenstore/xenstored_control.c
>>> +++ b/tools/xenstore/xenstored_control.c
>>> @@ -324,6 +324,7 @@ static const char *lu_binary_alloc(const void 
>>> *ctx, struct connection *conn,
>>>       lu_status->kernel_size = size;
>>>       lu_status->kernel_off = 0;
>>> +    errno = 0;
>>>       return NULL;
>>>   }
>>> @@ -339,6 +340,7 @@ static const char *lu_binary_save(const void 
>>> *ctx, struct connection *conn,
>>>       memcpy(lu_status->kernel + lu_status->kernel_off, data, size);
>>>       lu_status->kernel_off += size;
>>> +    errno = 0;
>>>       return NULL;
>>>   }
>>
>> I forgot to update lu_binary(). I will respin the patch once I get 
>> some feedback.
> 
> With setting errno to 0 before returning NULL in lu_binary() you can add
> 
> Reviewed-by: Juergen Gross <jgross@suse.com>

Thanks! I will commit it.

Cheers,

-- 
Julien Grall


      reply	other threads:[~2021-07-30 15:13 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29 11:06 [PATCH] tools/xenstored: Don't assume errno will not be overwritten in lu_arch() Julien Grall
2021-07-29 15:23 ` Julien Grall
2021-07-30  8:40   ` Juergen Gross
2021-07-30 15:13     ` Julien Grall [this message]

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