Patchwork getlogin_r: return early when linux sentinel value is set

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Submitter Jesse Hathaway
Date March 16, 2018, 4:18 p.m.
Message ID <CANSNSoWLXfsYq6kP0niyP8r25S=S1uTKN=+46xnC_SPLBmKXhQ@mail.gmail.com>
Download mbox | patch
Permalink /patch/26340/
State New
Headers show

Comments

Jesse Hathaway - March 16, 2018, 4:18 p.m.
When there is no login uid Linux sets /proc/self/loginid to the sentinel
value of 4294967295. If this is set we can return early and avoid
needlessly looking up the sentinel value in any configured nss
databases.
Jesse Hathaway - March 19, 2018, 3:03 p.m.
This is my first time submitting a patch, so any feedback would be
very much appreciated.

On Fri, Mar 16, 2018 at 11:18 AM, Jesse Hathaway <jesse@mbuki-mvuki.org> wrote:
> When there is no login uid Linux sets /proc/self/loginid to the sentinel
> value of 4294967295. If this is set we can return early and avoid
> needlessly looking up the sentinel value in any configured nss
> databases.
>
> diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
> b/sysdeps/unix/sysv/linux/getlogin_r.c
> index 73ea14c8f9..43f55a2188 100644
> --- a/sysdeps/unix/sysv/linux/getlogin_r.c
> +++ b/sysdeps/unix/sysv/linux/getlogin_r.c
> @@ -55,6 +55,12 @@ __getlogin_r_loginuid (char *name, size_t namesize)
>     endp == uidbuf || *endp != '\0'))
>      return -1;
>
> +  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
> +     value of 4294967295, so check if the value is set and return early to
> +     avoid making unneeded nss lookups. */
> +  if (uid == 4294967295)
> +    return ENXIO;
> +
>    struct passwd pwd;
>    struct passwd *tpwd;
>    int result = 0;
Adhemerval Zanella Netto - March 20, 2018, 8 a.m.
On 17/03/2018 00:18, Jesse Hathaway wrote:
> When there is no login uid Linux sets /proc/self/loginid to the sentinel
> value of 4294967295. If this is set we can return early and avoid
> needlessly looking up the sentinel value in any configured nss
> databases.

The change is short enough so I think it won't require a copyright
assignment.  However it does require a ChangeLog entry, could you please
resend the patch with a proper one?

> 
> diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
> b/sysdeps/unix/sysv/linux/getlogin_r.c
> index 73ea14c8f9..43f55a2188 100644
> --- a/sysdeps/unix/sysv/linux/getlogin_r.c
> +++ b/sysdeps/unix/sysv/linux/getlogin_r.c
> @@ -55,6 +55,12 @@ __getlogin_r_loginuid (char *name, size_t namesize)
>     endp == uidbuf || *endp != '\0'))
>      return -1;
> 
> +  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
> +     value of 4294967295, so check if the value is set and return early to
> +     avoid making unneeded nss lookups. */
> +  if (uid == 4294967295)
> +    return ENXIO;

I prefer to just use either (int)-1 or just 0xffffffff.  Also,
__getlogin_r_loginuid should set errno itself as for ERANGE instead
of just return its value (errno won't be set in this case and I think
it got it wrong for ENOMEM in this case).

> +
>    struct passwd pwd;
>    struct passwd *tpwd;
>    int result = 0;
>
Andreas Schwab - March 20, 2018, 9:05 a.m.
On Mär 20 2018, Adhemerval Zanella <adhemerval.zanella@linaro.org> wrote:

> On 17/03/2018 00:18, Jesse Hathaway wrote:
>> When there is no login uid Linux sets /proc/self/loginid to the sentinel
>> value of 4294967295. If this is set we can return early and avoid
>> needlessly looking up the sentinel value in any configured nss
>> databases.
>
> The change is short enough so I think it won't require a copyright
> assignment.  However it does require a ChangeLog entry, could you please
> resend the patch with a proper one?
>
>> 
>> diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
>> b/sysdeps/unix/sysv/linux/getlogin_r.c
>> index 73ea14c8f9..43f55a2188 100644
>> --- a/sysdeps/unix/sysv/linux/getlogin_r.c
>> +++ b/sysdeps/unix/sysv/linux/getlogin_r.c
>> @@ -55,6 +55,12 @@ __getlogin_r_loginuid (char *name, size_t namesize)
>>     endp == uidbuf || *endp != '\0'))
>>      return -1;
>> 
>> +  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
>> +     value of 4294967295, so check if the value is set and return early to
>> +     avoid making unneeded nss lookups. */
>> +  if (uid == 4294967295)
>> +    return ENXIO;
>
> I prefer to just use either (int)-1 or just 0xffffffff.

That should be (uid_t) -1.

Andreas.

Patch

diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
b/sysdeps/unix/sysv/linux/getlogin_r.c
index 73ea14c8f9..43f55a2188 100644
--- a/sysdeps/unix/sysv/linux/getlogin_r.c
+++ b/sysdeps/unix/sysv/linux/getlogin_r.c
@@ -55,6 +55,12 @@  __getlogin_r_loginuid (char *name, size_t namesize)
    endp == uidbuf || *endp != '\0'))
     return -1;

+  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
+     value of 4294967295, so check if the value is set and return early to
+     avoid making unneeded nss lookups. */
+  if (uid == 4294967295)
+    return ENXIO;
+
   struct passwd pwd;
   struct passwd *tpwd;
   int result = 0;