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SubjectRe: [RFC][PATCH] utsname: completely overwrite prior information
On Sat, Sep 13, 2008 at 12:11 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> fair enuf. Did you check allthe other fields in 'struct new_utsname'?

As far as I can tell, only nodename (hostname) and domainname may be
changed by userspace.

>
>> index 038a7bc..78b4515 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -1352,7 +1352,8 @@ asmlinkage long sys_sethostname(char __user *name, int len)
>> errno = -EFAULT;
>> if (!copy_from_user(tmp, name, len)) {
>> memcpy(utsname()->nodename, tmp, len);
>> - utsname()->nodename[len] = 0;
>> + memset(utsname()->nodename + len, 0,
>> + sizeof(utsname()->nodename) - len);
>
> We could do the memset before the memcpy. It's more work, but less
> text. Whatever.

Whatever :-)

> While we're there, the code generation in there is a bit sloppy. How's
> this look?
>
>
> From: Andrew Morton <akpm@linux-foundation.org>
>
> utsname() is quite expensive to calculate. Cache it in a local.
>
> text data bss dec hex filename
> before: 11136 720 16 11872 2e60 kernel/sys.o
> after: 11096 720 16 11832 2e38 kernel/sys.o
>
> Cc: Vegard Nossum <vegard.nossum@gmail.com>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: "Serge E. Hallyn" <serue@us.ibm.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

I agree with this change. FWIW: Acked-by: Vegard Nossum
<vegard.nossum@gmail.com>

There seems to be a few more places throughout the kernel which
needlessly call utsname() more than once. I will keep it in mind.

Thanks,


Vegard

--
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036


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