From c2109f05b7fd5d2e5472f45dbcc343786c504719 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 14 Feb 2019 15:02:18 -0800
Subject: [PATCH] Revert "exec: load_script: don't blindly truncate shebang
 string"

commit cb5b020a8d38f77209d0472a0fea755299a8ec78 upstream.

This reverts commit 8099b047ecc431518b9bb6bdbba3549bbecdc343.

It turns out that people do actually depend on the shebang string being
truncated, and on the fact that an interpreter (like perl) will often
just re-interpret it entirely to get the full argument list.

Reported-by: Samuel Dionne-Riel <samuel@dionne-riel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/binfmt_script.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index d0078cbb718b..7cde3f46ad26 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -42,14 +42,10 @@ static int load_script(struct linux_binprm *bprm)
 	fput(bprm->file);
 	bprm->file = NULL;
 
-	for (cp = bprm->buf+2;; cp++) {
-		if (cp >= bprm->buf + BINPRM_BUF_SIZE)
-			return -ENOEXEC;
-		if (!*cp || (*cp == '\n'))
-			break;
-	}
+	bprm->buf[BINPRM_BUF_SIZE - 1] = '\0';
+	if ((cp = strchr(bprm->buf, '\n')) == NULL)
+		cp = bprm->buf+BINPRM_BUF_SIZE-1;
 	*cp = '\0';
-
 	while (cp > bprm->buf) {
 		cp--;
 		if ((*cp == ' ') || (*cp == '\t'))
-- 
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