[Buildroot] [PATCH] package/meson: fix shabang in deep build trees

[Buildroot] [PATCH] package/meson: fix shabang in deep build trees

[Yann E. MORIN]

The meson script includes the full path to the python interpreter. In
deep build trees, this path can be more than 128 characters long, which
is the limit a shabang might be.

In older kernels, that was silently ignored, leading to potential bugs,
but newer kernels enforce that limit, and refuse to execve() the script,
returning with NOEXEC. Since the script is +x, the shell (any bourne
shell, as well as the C shell) will conclude from that situation that
they should interpret it as a shell script, which it obviously is not.

Fix the problem bu replacing the shabang with a call to /usr/bin/env
which will redirect to the correct pytohn3 interpreter found in the
PATH.

Note however that this means our meson installation can no longer be
called from outside of the meson-package infrastructure anymore (not
that we ever supported it before, but who knows what people may have
done in their br2-external), unless one does set the PATH to include
$(HOST_DIR)/bin/ earlier than a system-provided python3 would be found.

Fixes: #12331 #12461

Reported-by: Jean-pierre Cartal <jpcartal@free.fr>
Reported-by: Matthias Wei?er <m.weisser.m@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
---
 package/meson/meson.mk | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/package/meson/meson.mk b/package/meson/meson.mk
index d409ae7b52..179daaa38a 100644
--- a/package/meson/meson.mk
+++ b/package/meson/meson.mk
@@ -49,4 +49,10 @@ HOST_MESON_SED_CFLAGS = $(if $(strip $(TARGET_CFLAGS)),`printf '"%s"$(comma) ' $
 HOST_MESON_SED_LDFLAGS = $(if $(strip $(TARGET_LDFLAGS)),`printf '"%s"$(comma) ' $(TARGET_LDFLAGS)`)
 HOST_MESON_SED_CXXFLAGS = $(if $(strip $(TARGET_CXXFLAGS)),`printf '"%s"$(comma) ' $(TARGET_CXXFLAGS)`)
 
+# Avoid interpreter shabang longer than 127 chars
+define HOST_MESON_SET_INTERPRETER
+	$(SED) '1s:.*:#!/usr/bin/env python3:' $(HOST_DIR)/bin/meson
+endef
+HOST_MESON_POST_INSTALL_HOOKS += HOST_MESON_SET_INTERPRETER
+
 $(eval $(host-python-package))
-- 
2.20.1

[Buildroot] [PATCH] package/meson: fix shabang in deep build trees

[Arnout Vandecappelle]

On 13/01/2020 19:03, Yann E. MORIN wrote:
> The meson script includes the full path to the python interpreter. In
> deep build trees, this path can be more than 128 characters long, which
> is the limit a shabang might be.
> 
> In older kernels, that was silently ignored, leading to potential bugs,
> but newer kernels enforce that limit, and refuse to execve() the script,
> returning with NOEXEC. Since the script is +x, the shell (any bourne
> shell, as well as the C shell) will conclude from that situation that
> they should interpret it as a shell script, which it obviously is not.
> 
> Fix the problem bu replacing the shabang with a call to /usr/bin/env
> which will redirect to the correct pytohn3 interpreter found in the
> PATH.
> 
> Note however that this means our meson installation can no longer be
> called from outside of the meson-package infrastructure anymore (not
> that we ever supported it before, but who knows what people may have
> done in their br2-external), unless one does set the PATH to include
> $(HOST_DIR)/bin/ earlier than a system-provided python3 would be found.

Actually, since meson doesn't depend on any non-standard python package, using
the system-provided python3 is fine. In fact, IIRC the idea was to use the
system-provided python3 if available, but nobody ever implemented that.

 Regards,
 Arnout

> 
> Fixes: #12331 #12461
> 
> Reported-by: Jean-pierre Cartal <jpcartal@free.fr>
> Reported-by: Matthias Wei?er <m.weisser.m@gmail.com>
> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
> Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
> ---
>  package/meson/meson.mk | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/package/meson/meson.mk b/package/meson/meson.mk
> index d409ae7b52..179daaa38a 100644
> --- a/package/meson/meson.mk
> +++ b/package/meson/meson.mk
> @@ -49,4 +49,10 @@ HOST_MESON_SED_CFLAGS = $(if $(strip $(TARGET_CFLAGS)),`printf '"%s"$(comma) ' $
>  HOST_MESON_SED_LDFLAGS = $(if $(strip $(TARGET_LDFLAGS)),`printf '"%s"$(comma) ' $(TARGET_LDFLAGS)`)
>  HOST_MESON_SED_CXXFLAGS = $(if $(strip $(TARGET_CXXFLAGS)),`printf '"%s"$(comma) ' $(TARGET_CXXFLAGS)`)
>  
> +# Avoid interpreter shabang longer than 127 chars
> +define HOST_MESON_SET_INTERPRETER
> +	$(SED) '1s:.*:#!/usr/bin/env python3:' $(HOST_DIR)/bin/meson
> +endef
> +HOST_MESON_POST_INSTALL_HOOKS += HOST_MESON_SET_INTERPRETER
> +
>  $(eval $(host-python-package))
> 

[Buildroot] [PATCH] package/meson: fix shabang in deep build trees

[Peter Korsgaard]

>>>>> "Yann" == Yann E MORIN <yann.morin.1998@free.fr> writes:

 > The meson script includes the full path to the python interpreter. In
 > deep build trees, this path can be more than 128 characters long, which
 > is the limit a shabang might be.

NIT: It is called shebang, not shabang.

NIT2: This has actually been bumped to 256 bytes in linux 5.1:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6eb3c3d0a52dca337e327ae8868ca1f44a712e02

 > +# Avoid interpreter shabang longer than 127 chars

127? Off by one? ;) In fact, 128 bytes is the size of the entire buffer
read from the file, so including the leading #! and trailing \0 and the
actual path can AFAIK only be 125 bytes long. I changed it to 128 for
consistency.

Committed with these minor fixes, thanks.

-- 
Bye, Peter Korsgaard