[PATCH] libselinux: rename gettid() to something which never conflicts with the libc

[PATCH] libselinux: rename gettid() to something which never conflicts with the libc

[Nicolas Iooss]

Musl recently added a wrapper for gettid() syscall. There is no way to
detect this new version in a reliable way, so rename our gettid()
wrapper to a non-conflicting name.

Introduce a new function which, when using a libc known to provide a
wrapper for gettid(), calls it, and which, otherwise, performs the
syscall directly.

Anyway this function is only used on systems where /proc/thread-self
does not exist, which are therefore running Linux<3.17.

Fixes: https://github.com/SELinuxProject/selinux/issues/282
Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>

diff --git a/libselinux/src/procattr.c b/libselinux/src/procattr.c
index 1aa67ac53f39..840570525f5f 100644
--- a/libselinux/src/procattr.c
+++ b/libselinux/src/procattr.c
@@ -25,21 +25,23 @@ static __thread char destructor_initialized;
 /* Bionic and glibc >= 2.30 declare gettid() system call wrapper in unistd.h and
  * has a definition for it */
 #ifdef __BIONIC__
-  #define OVERRIDE_GETTID 0
+  #define HAVE_GETTID 1
 #elif !defined(__GLIBC_PREREQ)
-  #define OVERRIDE_GETTID 1
+  #define HAVE_GETTID 0
 #elif !__GLIBC_PREREQ(2,30)
-  #define OVERRIDE_GETTID 1
+  #define HAVE_GETTID 0
 #else
-  #define OVERRIDE_GETTID 0
+  #define HAVE_GETTID 1
 #endif
 
-#if OVERRIDE_GETTID
-static pid_t gettid(void)
+static pid_t selinux_gettid(void)
 {
+#if HAVE_GETTID
+	return gettid();
+#else
 	return syscall(__NR_gettid);
-}
 #endif
+}
 
 static void procattr_thread_destructor(void __attribute__((unused)) *unused)
 {
@@ -94,7 +96,7 @@ static int openattr(pid_t pid, const char *attr, int flags)
 		if (fd >= 0 || errno != ENOENT)
 			goto out;
 		free(path);
-		tid = gettid();
+		tid = selinux_gettid();
 		rc = asprintf(&path, "/proc/self/task/%d/attr/%s", tid, attr);
 	} else {
 		errno = EINVAL;
-- 
2.30.0

Re: [PATCH] libselinux: rename gettid() to something which never conflicts with the libc

[Petr Lautrbach]

Nicolas Iooss <nicolas.iooss@m4x.org> writes:

> Musl recently added a wrapper for gettid() syscall. There is no way to
> detect this new version in a reliable way, so rename our gettid()
> wrapper to a non-conflicting name.
>
> Introduce a new function which, when using a libc known to provide a
> wrapper for gettid(), calls it, and which, otherwise, performs the
> syscall directly.
>
> Anyway this function is only used on systems where /proc/thread-self
> does not exist, which are therefore running Linux<3.17.
>
> Fixes: https://github.com/SELinuxProject/selinux/issues/282
> Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>

Tested on Fedora with musl-1.2.22 scratch build
https://koji.fedoraproject.org/koji/taskinfo?taskID=62214131 :

Before
^&^ musl-gcc -D_GNU_SOURCE -I../include procattr.c -c
procattr.c:38:14: error: static declaration of ‘gettid’ follows non-static declaration
   38 | static pid_t gettid(void)
      |              ^~~~~~
In file included from procattr.c:2:
/usr/x86_64-linux-musl/include/unistd.h:194:7: note: previous declaration of ‘gettid’ with type ‘pid_t(void)’ {aka ‘int(void)’}
  194 | pid_t gettid(void);
      |       ^~~~~~


After
^&^ musl-gcc -D_GNU_SOURCE -I../include procattr.c -c


Seems to work. Thanks!

Acked-by: Petr Lautrbach <plautrba@redhat.com>



> diff --git a/libselinux/src/procattr.c b/libselinux/src/procattr.c
> index 1aa67ac53f39..840570525f5f 100644
> --- a/libselinux/src/procattr.c
> +++ b/libselinux/src/procattr.c
> @@ -25,21 +25,23 @@ static __thread char destructor_initialized;
>  /* Bionic and glibc >= 2.30 declare gettid() system call wrapper in unistd.h and
>   * has a definition for it */
>  #ifdef __BIONIC__
> -  #define OVERRIDE_GETTID 0
> +  #define HAVE_GETTID 1
>  #elif !defined(__GLIBC_PREREQ)
> -  #define OVERRIDE_GETTID 1
> +  #define HAVE_GETTID 0
>  #elif !__GLIBC_PREREQ(2,30)
> -  #define OVERRIDE_GETTID 1
> +  #define HAVE_GETTID 0
>  #else
> -  #define OVERRIDE_GETTID 0
> +  #define HAVE_GETTID 1
>  #endif
>  
> -#if OVERRIDE_GETTID
> -static pid_t gettid(void)
> +static pid_t selinux_gettid(void)
>  {
> +#if HAVE_GETTID
> +	return gettid();
> +#else
>  	return syscall(__NR_gettid);
> -}
>  #endif
> +}
>  
>  static void procattr_thread_destructor(void __attribute__((unused)) *unused)
>  {
> @@ -94,7 +96,7 @@ static int openattr(pid_t pid, const char *attr, int flags)
>  		if (fd >= 0 || errno != ENOENT)
>  			goto out;
>  		free(path);
> -		tid = gettid();
> +		tid = selinux_gettid();
>  		rc = asprintf(&path, "/proc/self/task/%d/attr/%s", tid, attr);
>  	} else {
>  		errno = EINVAL;
> -- 
> 2.30.0

Re: [PATCH] libselinux: rename gettid() to something which never conflicts with the libc

[Petr Lautrbach]

Petr Lautrbach <plautrba@redhat.com> writes:

> Nicolas Iooss <nicolas.iooss@m4x.org> writes:
>
>> Musl recently added a wrapper for gettid() syscall. There is no way to
>> detect this new version in a reliable way, so rename our gettid()
>> wrapper to a non-conflicting name.
>>
>> Introduce a new function which, when using a libc known to provide a
>> wrapper for gettid(), calls it, and which, otherwise, performs the
>> syscall directly.
>>
>> Anyway this function is only used on systems where /proc/thread-self
>> does not exist, which are therefore running Linux<3.17.
>>
>> Fixes: https://github.com/SELinuxProject/selinux/issues/282
>> Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>
>
> Tested on Fedora with musl-1.2.22 scratch build
> https://koji.fedoraproject.org/koji/taskinfo?taskID=62214131 :
>
> Before
> ^&^ musl-gcc -D_GNU_SOURCE -I../include procattr.c -c
> procattr.c:38:14: error: static declaration of ‘gettid’ follows non-static declaration
>    38 | static pid_t gettid(void)
>       |              ^~~~~~
> In file included from procattr.c:2:
> /usr/x86_64-linux-musl/include/unistd.h:194:7: note: previous declaration of ‘gettid’ with type ‘pid_t(void)’ {aka ‘int(void)’}
>   194 | pid_t gettid(void);
>       |       ^~~~~~
>
>
> After
> ^&^ musl-gcc -D_GNU_SOURCE -I../include procattr.c -c
>
>
> Seems to work. Thanks!
>
> Acked-by: Petr Lautrbach <plautrba@redhat.com>
>

Merged.


>
>> diff --git a/libselinux/src/procattr.c b/libselinux/src/procattr.c
>> index 1aa67ac53f39..840570525f5f 100644
>> --- a/libselinux/src/procattr.c
>> +++ b/libselinux/src/procattr.c
>> @@ -25,21 +25,23 @@ static __thread char destructor_initialized;
>>  /* Bionic and glibc >= 2.30 declare gettid() system call wrapper in unistd.h and
>>   * has a definition for it */
>>  #ifdef __BIONIC__
>> -  #define OVERRIDE_GETTID 0
>> +  #define HAVE_GETTID 1
>>  #elif !defined(__GLIBC_PREREQ)
>> -  #define OVERRIDE_GETTID 1
>> +  #define HAVE_GETTID 0
>>  #elif !__GLIBC_PREREQ(2,30)
>> -  #define OVERRIDE_GETTID 1
>> +  #define HAVE_GETTID 0
>>  #else
>> -  #define OVERRIDE_GETTID 0
>> +  #define HAVE_GETTID 1
>>  #endif
>>  
>> -#if OVERRIDE_GETTID
>> -static pid_t gettid(void)
>> +static pid_t selinux_gettid(void)
>>  {
>> +#if HAVE_GETTID
>> +	return gettid();
>> +#else
>>  	return syscall(__NR_gettid);
>> -}
>>  #endif
>> +}
>>  
>>  static void procattr_thread_destructor(void __attribute__((unused)) *unused)
>>  {
>> @@ -94,7 +96,7 @@ static int openattr(pid_t pid, const char *attr, int flags)
>>  		if (fd >= 0 || errno != ENOENT)
>>  			goto out;
>>  		free(path);
>> -		tid = gettid();
>> +		tid = selinux_gettid();
>>  		rc = asprintf(&path, "/proc/self/task/%d/attr/%s", tid, attr);
>>  	} else {
>>  		errno = EINVAL;
>> -- 
>> 2.30.0