Add a personality to report 2.6.x version numbers

I ran into a couple of programs which broke with the new Linux 3.0
version.  Some of those were binary only.  I tried to use LD_PRELOAD to
work around it, but it was quite difficult and in one case impossible
because of a mix of 32bit and 64bit executables.

For example, all kind of management software from HP doesnt work, unless
we pretend to run a 2.6 kernel.

  $ uname -a
  Linux svivoipvnx001 3.0.0-08107-g97cd98f #1062 SMP Fri Aug 12 18:11:45 CEST 2011 i686 i686 i386 GNU/Linux

  $ hpacucli ctrl all show

  Error: No controllers detected.

  $ rpm -qf /usr/sbin/hpacucli
  hpacucli-8.75-12.0

Another notable case is that Python now reports "linux3" from
sys.platform(); which in turn can break things that were checking
sys.platform() == "linux2":

  https://bugzilla.mozilla.org/show_bug.cgi?id=664564

It seems pretty clear to me though it's a bug in the apps that are using
'==' instead of .startswith(), but this allows us to unbreak broken
programs.

This patch adds a UNAME26 personality that makes the kernel report a
2.6.40+x version number instead.  The x is the x in 3.x.

I know this is somewhat ugly, but I didn't find a better workaround, and
compatibility to existing programs is important.

Some programs also read /proc/sys/kernel/osrelease.  This can be worked
around in user space with mount --bind (and a mount namespace)

To use:

  wget ftp://ftp.kernel.org/pub/linux/kernel/people/ak/uname26/uname26.c
  gcc -o uname26 uname26.c
  ./uname26 program
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/personality.h

@@ -22,6 +22,7 @@ extern int		__set_personality(unsigned int);
  * These occupy the top three bytes.
  */
 enum {
+	UNAME26	=               0x0020000,
 	ADDR_NO_RANDOMIZE = 	0x0040000,	/* disable randomization of VA space */
 	FDPIC_FUNCPTRS =	0x0080000,	/* userspace function ptrs point to descriptors
 						 * (signal handling)

kernel/sys.c

@@ -37,6 +37,8 @@
 #include <linux/fs_struct.h>
 #include <linux/gfp.h>
 #include <linux/syscore_ops.h>
+#include <linux/version.h>
+#include <linux/ctype.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -44,6 +46,8 @@
 #include <linux/user_namespace.h>
 
 #include <linux/kmsg_dump.h>
+/* Move somewhere else to avoid recompiling? */
+#include <generated/utsrelease.h>
 
 #include <asm/uaccess.h>
 #include <asm/io.h>
@@ -1161,6 +1165,34 @@ DECLARE_RWSEM(uts_sem);
 #define override_architecture(name)	0
 #endif
 
+/*
+ * Work around broken programs that cannot handle "Linux 3.0".
+ * Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40
+ */
+static int override_release(char __user *release, int len)
+{
+	int ret = 0;
+	char buf[len];
+
+	if (current->personality & UNAME26) {
+		char *rest = UTS_RELEASE;
+		int ndots = 0;
+		unsigned v;
+
+		while (*rest) {
+			if (*rest == '.' && ++ndots >= 3)
+				break;
+			if (!isdigit(*rest) && *rest != '.')
+				break;
+			rest++;
+		}
+		v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
+		snprintf(buf, len, "2.6.%u%s", v, rest);
+		ret = copy_to_user(release, buf, len);
+	}
+	return ret;
+}
+
 SYSCALL_DEFINE1(newuname, struct new_utsname __user *, name)
 {
 	int errno = 0;
@@ -1170,6 +1202,8 @@ SYSCALL_DEFINE1(newuname, struct new_utsname __user *, name)
 		errno = -EFAULT;
 	up_read(&uts_sem);
 
+	if (!errno && override_release(name->release, sizeof(name->release)))
+		errno = -EFAULT;
 	if (!errno && override_architecture(name))
 		errno = -EFAULT;
 	return errno;
@@ -1191,6 +1225,8 @@ SYSCALL_DEFINE1(uname, struct old_utsname __user *, name)
 		error = -EFAULT;
 	up_read(&uts_sem);
 
+	if (!error && override_release(name->release, sizeof(name->release)))
+		error = -EFAULT;
 	if (!error && override_architecture(name))
 		error = -EFAULT;
 	return error;
@@ -1225,6 +1261,8 @@ SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
 
 	if (!error && override_architecture(name))
 		error = -EFAULT;
+	if (!error && override_release(name->release, sizeof(name->release)))
+		error = -EFAULT;
 	return error ? -EFAULT : 0;
 }
 #endif