From 8890b29341f30f4a364b2eb6046bb1ac1478f955 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sat, 4 Apr 2020 09:42:56 -0500 Subject: exec: Move handling of the point of no return to the top level 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 Link: https://lkml.kernel.org/r/87y2q25knl.fsf_-_@x220.int.ebiederm.org Signed-off-by: "Eric W. Biederman" --- fs/exec.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index ecee0ebebf85..fa265ea322b7 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -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); -- cgit v1.2.3