Re: [PATCHv4 2/3] fs: Make core dump functionality optional

[Serge Hallyn <serge.hallyn@canonical.com>]

Quoting Alex Kelly (alex.page.kelly@gmail.com):
> Adds an expert Kconfig option, CONFIG_COREDUMP, which allows disabling of core dump.
> This saves approximately 2.6k in the compiled kernel, and complements CONFIG_ELF_CORE,
> which now depends on it.

Is there another reason than the 2.6k to do this?  My kernels range
between 4.8 and 5M, so that's .05% size savings?

I'm not saying nack (it's not my area anyway), just seem to be missing
the point.

> CONFIG_COREDUMP also disables coredump-related sysctls, except for suid_dumpable and
> related functions, which are necessary for ptrace.
> 
> Signed-off-by: Alex Kelly <alex.page.kelly@gmail.com>
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> ---
>  fs/Kconfig.binfmt       | 8 ++++++++
>  fs/Makefile             | 3 ++-
>  include/linux/binfmts.h | 4 ++++
>  init/Kconfig            | 1 +
>  kernel/sysctl.c         | 6 +++++-
>  5 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index 0225742..0efd152 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -164,3 +164,11 @@ config BINFMT_MISC
>  	  You may say M here for module support and later load the module when
>  	  you have use for it; the module is called binfmt_misc. If you
>  	  don't know what to answer at this point, say Y.
> +
> +config COREDUMP
> +	bool "Enable core dump support" if EXPERT
> +	default y
> +	help
> +	  This option enables support for performing core dumps. You almost
> +	  certainly want to say Y here. Not necessary on systems that never
> +	  need debugging or only ever run flawless code.
> diff --git a/fs/Makefile b/fs/Makefile
> index 8938f82..1d7af79 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -11,7 +11,7 @@ obj-y :=	open.o read_write.o file_table.o super.o \
>  		attr.o bad_inode.o file.o filesystems.o namespace.o \
>  		seq_file.o xattr.o libfs.o fs-writeback.o \
>  		pnode.o drop_caches.o splice.o sync.o utimes.o \
> -		stack.o fs_struct.o statfs.o coredump.o
> +		stack.o fs_struct.o statfs.o
>  
>  ifeq ($(CONFIG_BLOCK),y)
>  obj-y +=	buffer.o bio.o block_dev.o direct-io.o mpage.o ioprio.o
> @@ -48,6 +48,7 @@ obj-$(CONFIG_FS_MBCACHE)	+= mbcache.o
>  obj-$(CONFIG_FS_POSIX_ACL)	+= posix_acl.o xattr_acl.o
>  obj-$(CONFIG_NFS_COMMON)	+= nfs_common/
>  obj-$(CONFIG_GENERIC_ACL)	+= generic_acl.o
> +obj-$(CONFIG_COREDUMP)		+= coredump.o
>  
>  obj-$(CONFIG_FHANDLE)		+= fhandle.o
>  
> diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
> index 366422b..00e2e89 100644
> --- a/include/linux/binfmts.h
> +++ b/include/linux/binfmts.h
> @@ -132,7 +132,11 @@ extern int copy_strings_kernel(int argc, const char *const *argv,
>  			       struct linux_binprm *bprm);
>  extern int prepare_bprm_creds(struct linux_binprm *bprm);
>  extern void install_exec_creds(struct linux_binprm *bprm);
> +#ifdef CONFIG_COREDUMP
>  extern void do_coredump(long signr, int exit_code, struct pt_regs *regs);
> +#else
> +static inline void do_coredump(long signr, int exit_code, struct pt_regs *regs) {}
> +#endif
>  extern void set_binfmt(struct linux_binfmt *new);
>  extern void free_bprm(struct linux_binprm *);
>  
> diff --git a/init/Kconfig b/init/Kconfig
> index af6c7f8..0e75056 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1230,6 +1230,7 @@ config BUG
>            Just say Y.
>  
>  config ELF_CORE
> +	depends on COREDUMP
>  	default y
>  	bool "Enable ELF core dumps" if EXPERT
>  	help
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 87174ef..af57e84 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -97,10 +97,12 @@
>  extern int sysctl_overcommit_memory;
>  extern int sysctl_overcommit_ratio;
>  extern int max_threads;
> -extern int core_uses_pid;
>  extern int suid_dumpable;
> +#ifdef CONFIG_COREDUMP
> +extern int core_uses_pid;
>  extern char core_pattern[];
>  extern unsigned int core_pipe_limit;
> +#endif
>  extern int pid_max;
>  extern int min_free_kbytes;
>  extern int pid_max_min, pid_max_max;
> @@ -404,6 +406,7 @@ static struct ctl_table kern_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +#ifdef CONFIG_COREDUMP
>  	{
>  		.procname	= "core_uses_pid",
>  		.data		= &core_uses_pid,
> @@ -425,6 +428,7 @@ static struct ctl_table kern_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec,
>  	},
> +#endif
>  #ifdef CONFIG_PROC_SYSCTL
>  	{
>  		.procname	= "tainted",
> -- 
> 1.7.11.2
>