[PATCH] fs: Make binfmt support for #! scripts modular and removable

[Josh Triplett <josh@joshtriplett.org>]

Add a new configuration option CONFIG_BINFMT_SCRIPT to configure support
for interpreted scripts starting with "#!"; allow compiling out that
support, or building it as a module.  Embedded systems running
exclusively compiled binaries could leave this support out, and systems
that don't need scripts before mounting the root filesystem can build
this as a module.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---

Note when testing this that many shells implement support for shell
scripts themselves, so try it with something like #!/bin/cat instead.

 fs/Kconfig.binfmt |   14 ++++++++++++++
 fs/Makefile       |    5 +----
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index 0efd152..370b24c 100644
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -65,6 +65,20 @@ config CORE_DUMP_DEFAULT_ELF_HEADERS
 	  This config option changes the default setting of coredump_filter
 	  seen at boot time.  If unsure, say Y.
 
+config BINFMT_SCRIPT
+	tristate "Kernel support for scripts starting with #!"
+	default y
+	help
+	  Say Y here if you want to execute interpreted scripts starting with
+	  #! followed by the path to an interpreter.
+
+	  You can build this support as a module; however, until that module
+	  gets loaded, you cannot run scripts.  Thus, if you want to load this
+	  module from an initramfs, the portion of the initramfs before loading
+	  this module must consist of compiled binaries only.
+
+	  Most systems will not boot if you say M or N here.  If unsure, say Y.
+
 config BINFMT_FLAT
 	bool "Kernel support for flat binaries"
 	depends on !MMU && (!FRV || BROKEN)
diff --git a/fs/Makefile b/fs/Makefile
index 9d53192..2ef3298 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -34,10 +34,7 @@ obj-$(CONFIG_COMPAT)		+= compat.o compat_ioctl.o
 obj-$(CONFIG_BINFMT_AOUT)	+= binfmt_aout.o
 obj-$(CONFIG_BINFMT_EM86)	+= binfmt_em86.o
 obj-$(CONFIG_BINFMT_MISC)	+= binfmt_misc.o
-
-# binfmt_script is always there
-obj-y				+= binfmt_script.o
-
+obj-$(CONFIG_BINFMT_SCRIPT)	+= binfmt_script.o
 obj-$(CONFIG_BINFMT_ELF)	+= binfmt_elf.o
 obj-$(CONFIG_COMPAT_BINFMT_ELF)	+= compat_binfmt_elf.o
 obj-$(CONFIG_BINFMT_ELF_FDPIC)	+= binfmt_elf_fdpic.o
-- 
1.7.10.4