Commit c2315c18 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

exec: load_script: kill the onstack interp[BINPRM_BUF_SIZE] array 

Patch series "exec: binfmt_misc: fix use-after-free, kill
iname[BINPRM_BUF_SIZE]".

It looks like this code was always wrong, then commit 948b701a
("binfmt_misc: add persistent opened binary handler for containers")
added more problems.

This patch (of 6):

load_script() can simply use i_name instead, it points into bprm->buf[]
and nobody can change this memory until we call prepare_binprm().

The only complication is that we need to also change the signature of
bprm_change_interp() but this change looks good too.

While at it, do whitespace/style cleanups.

NOTE: the real motivation for this change is that people want to
increase BINPRM_BUF_SIZE, we need to change load_misc_binary() too but
this looks more complicated because afaics it is very buggy.

Link: http://lkml.kernel.org/r/20170918163446.GA26793@redhat.com


Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Cc: Travis Gummels <tgummels@redhat.com>
Cc: Ben Woodard <woodard@redhat.com>
Cc: Jim Foraker <foraker1@llnl.gov>
Cc: <tdhooge@llnl.gov>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 384632e6

fs/binfmt_script.c

+9 −8
Original line number Diff line number Diff line
@@ -19,7 +19,6 @@ static int load_script(struct linux_binprm *bprm) 
	const char *i_arg, *i_name;

	char *cp;

	struct file *file;

	char interp[BINPRM_BUF_SIZE];

	int retval;



	if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
@@ -65,7 +64,6 @@ static int load_script(struct linux_binprm *bprm) 
		*cp++ = '\0';

	if (*cp)

		i_arg = cp;

	strcpy (interp, i_name);

	/*

	 * OK, we've parsed out the interpreter name and

	 * (optional) argument.
@@ -80,24 +78,27 @@ static int load_script(struct linux_binprm *bprm) 
	if (retval)

		return retval;

	retval = copy_strings_kernel(1, &bprm->interp, bprm);

	if (retval < 0) return retval; 

	if (retval < 0)

		return retval;

	bprm->argc++;

	if (i_arg) {

		retval = copy_strings_kernel(1, &i_arg, bprm);

		if (retval < 0) return retval; 

		if (retval < 0)

			return retval;

		bprm->argc++;

	}

	retval = copy_strings_kernel(1, &i_name, bprm);

	if (retval) return retval; 

	if (retval)

		return retval;

	bprm->argc++;

	retval = bprm_change_interp(interp, bprm);

	retval = bprm_change_interp(i_name, bprm);

	if (retval < 0)

		return retval;



	/*

	 * OK, now restart the process with the interpreter's dentry.

	 */

	file = open_exec(interp);

	file = open_exec(i_name);

	if (IS_ERR(file))

		return PTR_ERR(file);

fs/exec.c

+1 −1
Original line number Diff line number Diff line
@@ -1410,7 +1410,7 @@ static void free_bprm(struct linux_binprm *bprm) 
	kfree(bprm);

}



int bprm_change_interp(char *interp, struct linux_binprm *bprm)

int bprm_change_interp(const char *interp, struct linux_binprm *bprm)

{

	/* If a binfmt changed the interp, free it first. */

	if (bprm->interp != bprm->filename)

include/linux/binfmts.h

+1 −1
Original line number Diff line number Diff line
@@ -131,7 +131,7 @@ extern int setup_arg_pages(struct linux_binprm * bprm, 
			   int executable_stack);

extern int transfer_args_to_stack(struct linux_binprm *bprm,

				  unsigned long *sp_location);

extern int bprm_change_interp(char *interp, struct linux_binprm *bprm);

extern int bprm_change_interp(const char *interp, struct linux_binprm *bprm);

extern int copy_strings_kernel(int argc, const char *const *argv,

			       struct linux_binprm *bprm);

extern int prepare_bprm_creds(struct linux_binprm *bprm);

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