Re: [PATCH] Add a personality to report 2.6.x version numbers

[Arnaud Lacombe]

Hi,

On Fri, Aug 19, 2011 at 7:15 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>
> Reposting due to popular demand. Several other people are running
> into the same problem with all kinds of software.
>
> Only change is rebase against current master.
>
FWIW, couldn't this be made a boot option ?

That might help some distros, say Fedora, who actually ships
2.6.40+x-branded kernels, or allow people to use no longer supported
distros with recent kernels.

About this last point, once functional, I intend to upgrade my trixbox
install (based on 2.6.18) to a 3.x-ish kernel, that might be fun...

Thanks,
 - Arnaud

> -Andi
>
> --
>
> 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.
>
> 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@xxxxxxxxxxxxxxx>
> ---
>  include/linux/personality.h |    1 +
>  kernel/sys.c                |   38 ++++++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/personality.h b/include/linux/personality.h
> index eec3bae..8fc7dd1a 100644
> --- a/include/linux/personality.h
> +++ b/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)
> diff --git a/kernel/sys.c b/kernel/sys.c
> index a101ba3..bd6d142 100644
> --- a/kernel/sys.c
> +++ b/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>
> @@ -1154,6 +1158,34 @@ 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;
> @@ -1163,6 +1195,8 @@ 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;
> @@ -1184,6 +1218,8 @@ 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;
> @@ -1218,6 +1254,8 @@ 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
> --
> 1.7.4.4
>
> --
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