From 61b5e58f18f152636a77c872dc39281bfb8bf90d Mon Sep 17 00:00:00 2001
From: Tobias Stoeckmann <tobias@stoeckmann.org>
Date: Fri, 17 Jan 2020 20:49:33 +0100
Subject: [PATCH] sed: handle very long execution lines (tiny change)

If sed is called with an excessively long execution line, then it is
prone to an out of bounds memory access.

The problem is that the length of the execution line, which is a
size_t, is temporarily stored in an int. This means that on systems
which have a 64 bit size_t and a 32 bit int (e.g. linux amd64) an
execution line which exceeds 2 GB will overflow int. If it is just
slightly larger than 2 GB, the negative int value is used as an
array index to finish the execution line string with '\0' which
therefore triggers the out of bounds access.

This problem is probably never triggered in reality, but can be
provoked like this (given that 'e' support is compiled in):

$ dd if=/dev/zero bs=1M count=2049 | tr '\0' e > e-command.txt
$ sed -f e-command.txt /etc/fstab
Segmentation fault (core dumped)

Also adjust another int/size_t conversion, even though it is a
purely cosmetic change, because it can never be larger than 4096.

* sed/execute.c (execute_program) [case 'e']: Declare cmd_length
to be of type size_t, not int.  Likewise for "n" just below.
* NEWS (Bug fixes): Mention it.
This addresses https://bugs.gnu.org/39165
---
 sed/execute.c | 4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/sed/execute.c b/sed/execute.c
index c5f07cc..8f43f2e 100644
--- a/sed/execute.c
+++ b/sed/execute.c
@@ -1347,7 +1347,7 @@ execute_program (struct vector *vec, struct input *input)
               panic (_("`e' command not supported"));
 #else
               FILE *pipe_fp;
-              int cmd_length = cur_cmd->x.cmd_txt.text_length;
+              size_t cmd_length = cur_cmd->x.cmd_txt.text_length;
               line_reset (&s_accum, NULL);
 
               if (!cmd_length)
@@ -1367,7 +1367,7 @@ execute_program (struct vector *vec, struct input *input)
 
               {
                 char buf[4096];
-                int n;
+                size_t n;
                 while (!feof (pipe_fp))
                   if ((n = fread (buf, sizeof (char), 4096, pipe_fp)) > 0)
                     {