exec: Move handling of the point of no return to the top level (8890b293) · Commits · 戴 / test

Move the handing of the point of no return from search_binary_handler into __do_execve_file so that it is easier to find, and to keep things robust in the face of change. Make it clear that an existing fatal signal will take precedence over a forced SIGSEGV by not forcing SIGSEGV if a fatal signal is already pending. This does not change the behavior but it saves a reader of the code the tedium of reading and understanding force_sig and the signal delivery code. Update the comment in begin_new_exec about where SIGSEGV is forced. Keep point_of_no_return from being a mystery by documenting what the code is doing where it forces SIGSEGV if the code is past the point of no return. Reviewed-by:

Kees Cook <keescook@chromium.org> Link: https://lkml.kernel.org/r/87y2q25knl.fsf_-_@x220.int.ebiederm.org Signed-off-by:

"Eric W. Biederman" <ebiederm@xmission.com>

fs/exec.c

+12 −9

Original line number	Diff line number	Diff line
		@@ -1329,8 +1329,8 @@ int begin_new_exec(struct linux_binprm * bprm)
		/*
		* With the new mm installed it is completely impossible to
		* fail and return to the original process. If anything from
		* here on returns an error, the check in
		* search_binary_handler() will SEGV current.
		* here on returns an error, the check in __do_execve_file()
		* will SEGV current.
		*/
		bprm->point_of_no_return = true;
		bprm->mm = NULL;
		@@ -1721,13 +1721,8 @@ int search_binary_handler(struct linux_binprm *bprm)

		read_lock(&binfmt_lock);
		put_binfmt(fmt);
		if (retval < 0 && bprm->point_of_no_return) {
		/* we got to flush_old_exec() and failed after it */
		read_unlock(&binfmt_lock);
		force_sigsegv(SIGSEGV);
		return retval;
		}
		if (retval != -ENOEXEC \|\| !bprm->file) {
		if (bprm->point_of_no_return \|\| !bprm->file \|\|
		(retval != -ENOEXEC)) {
		read_unlock(&binfmt_lock);
		return retval;
		}
		@@ -1898,6 +1893,14 @@ static int __do_execve_file(int fd, struct filename *filename,
		return retval;

		out:
		/*
		* If past the point of no return ensure the the code never
		* returns to the userspace process. Use an existing fatal
		* signal if present otherwise terminate the process with
		* SIGSEGV.
		*/
		if (bprm->point_of_no_return && !fatal_signal_pending(current))
		force_sigsegv(SIGSEGV);
		if (bprm->mm) {
		acct_arg_size(bprm, 0);
		mmput(bprm->mm);

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