Commit fa1bdca9 authored by Nir Lichtman's avatar Nir Lichtman Committed by Kees Cook
Browse files

exec: remove legacy custom binfmt modules autoloading 



Problem: The search binary handler logic contains legacy code
to handle automatically loading kernel modules of unsupported
binary formats.
This logic is a leftover from a.out-to-ELF transition.
After removal of a.out support, this code has no use anymore.

Solution: Clean up this code from the search binary handler,
also remove the line initialising retval to -ENOENT and instead
just return -ENOEXEC if the flow has reached the end of the func.

Note: Anyone who might find future uses for this legacy code
would be better off using binfmt_misc to trigger whatever
module loading they might need - would be more flexible that way.

Suggested-by: default avatarAlexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarNir Lichtman <nir@lichtman.org>
Link: https://lore.kernel.org/r/20241116231323.GA225987@lichtman.org


Signed-off-by: default avatarKees Cook <kees@kernel.org>
parent 4188fc31

fs/exec.c

+1 −15
Original line number Diff line number Diff line
@@ -1723,13 +1723,11 @@ int remove_arg_zero(struct linux_binprm *bprm) 
}

EXPORT_SYMBOL(remove_arg_zero);



#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))

/*

 * cycle the list of binary formats handler, until one recognizes the image

 */

static int search_binary_handler(struct linux_binprm *bprm)

{

	bool need_retry = IS_ENABLED(CONFIG_MODULES);

	struct linux_binfmt *fmt;

	int retval;
@@ -1741,8 +1739,6 @@ static int search_binary_handler(struct linux_binprm *bprm) 
	if (retval)

		return retval;



	retval = -ENOENT;

 retry:

	read_lock(&binfmt_lock);

	list_for_each_entry(fmt, &formats, lh) {

		if (!try_module_get(fmt->module))
@@ -1760,17 +1756,7 @@ static int search_binary_handler(struct linux_binprm *bprm) 
	}

	read_unlock(&binfmt_lock);



	if (need_retry) {

		if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&

		    printable(bprm->buf[2]) && printable(bprm->buf[3]))

			return retval;

		if (request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2)) < 0)

			return retval;

		need_retry = false;

		goto retry;

	}



	return retval;

	return -ENOEXEC;

}



/* binfmt handlers will call back into begin_new_exec() on success. */