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

From: Josh Triplett
Date: Wed Mar 13 2013 - 17:38:23 EST

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@xxxxxxxxxxxxxxxx>

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.

+ 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.
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

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