[PATCH] make uselib configurable (was Re: uselib() & 2.6.X?)

["Barry K. Nathan" <barryn@pobox.com>]

On Sat, Jan 08, 2005 at 10:46:19AM -0800, Linus Torvalds wrote:
> Another issue is likely that we should make the whole "uselib()"
> interfaces configurable. I don't think modern binaries use it (where
> "modern" probably means "compiled within the last 8 years" ;).

Here's an initial stab at such a patch. It adds a new config option,
CONFIG_SYS_USELIB. I wrote the patch against 2.6.10-bk14 but I tested it
against vanilla 2.6.10. Also, it only updates defconfig for i386, as
that's the only platform I can test at the moment.

There's probably plenty to criticize in this patch, but it's a start...

Signed-off-by: Barry K. Nathan <barryn@pobox.com>

diff -ruN linux-2.6.10-bk14/arch/i386/defconfig linux-2.6.10-bk14-bkn1/arch/i386/defconfig
--- linux-2.6.10-bk14/arch/i386/defconfig	2005-01-11 09:38:04.847566774 -0800
+++ linux-2.6.10-bk14-bkn1/arch/i386/defconfig	2005-01-11 11:15:02.127586567 -0800
@@ -195,6 +195,7 @@
 #
 # Executable file formats
 #
+CONFIG_SYS_USELIB=y
 CONFIG_BINFMT_ELF=y
 CONFIG_BINFMT_AOUT=y
 CONFIG_BINFMT_MISC=y
diff -ruN linux-2.6.10-bk14/fs/exec.c linux-2.6.10-bk14-bkn1/fs/exec.c
--- linux-2.6.10-bk14/fs/exec.c	2005-01-11 09:38:26.215892759 -0800
+++ linux-2.6.10-bk14-bkn1/fs/exec.c	2005-01-11 11:06:19.482007489 -0800
@@ -111,6 +111,7 @@
 	module_put(fmt->module);
 }
 
+#ifdef CONFIG_SYS_USELIB
 /*
  * Note that a shared library must be both readable and executable due to
  * security reasons.
@@ -167,6 +168,7 @@
 	path_release(&nd);
 	goto out;
 }
+#endif
 
 /*
  * count() counts the number of strings in array ARGV.
diff -ruN linux-2.6.10-bk14/fs/Kconfig.binfmt linux-2.6.10-bk14-bkn1/fs/Kconfig.binfmt
--- linux-2.6.10-bk14/fs/Kconfig.binfmt	2005-01-11 09:38:25.702932946 -0800
+++ linux-2.6.10-bk14-bkn1/fs/Kconfig.binfmt	2005-01-11 11:09:16.873962890 -0800
@@ -1,3 +1,16 @@
+config SYS_USELIB
+	bool "sys_uselib syscall support (needed for old binaries)"
+	---help---
+	  Many old binaries (e.g. dynamically linked a.out binaries, and
+	  ELF binaries that are dynamically linked against libc5), require
+	  the sys_uselib syscall. However, on the typical Linux system, this
+	  code is just old cruft that no longer serves a purpose.
+
+	  If you are unsure, say "N" if you care more about security and
+	  trimming bloat, or say "Y" if you care more about compatibility
+	  with old software. (If you will answer "Y" or "M" to BINFMT_AOUT,
+	  below, you probably should answer "Y" here.)
+
 config BINFMT_ELF
 	bool "Kernel support for ELF binaries"
 	depends on MMU
diff -ruN linux-2.6.10-bk14/kernel/sys_ni.c linux-2.6.10-bk14-bkn1/kernel/sys_ni.c
--- linux-2.6.10-bk14/kernel/sys_ni.c	2004-12-14 03:18:07.379372435 -0800
+++ linux-2.6.10-bk14-bkn1/kernel/sys_ni.c	2005-01-11 13:25:38.670751478 -0800
@@ -76,6 +76,7 @@
 cond_syscall(sys_keyctl)
 cond_syscall(compat_sys_keyctl)
 cond_syscall(compat_sys_socketcall)
+cond_syscall(sys_uselib)
 
 /* arch-specific weak syscall entries */
 cond_syscall(sys_pciconfig_read)