File 0029-net-http-Fix-OOB-write-for-split-http-headers.patch of Package grub2.28511

From a1c75b25aeb9b667ca9de1b5859f2f367c6aafdb Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Tue, 8 Mar 2022 18:17:03 +1100
Subject: [PATCH 29/37] net/http: Fix OOB write for split http headers

GRUB has special code for handling an http header that is split
across two packets.

The code tracks the end of line by looking for a "\n" byte. The
code for split headers has always advanced the pointer just past the
end of the line, whereas the code that handles unsplit headers does
not advance the pointer. This extra advance causes the length to be
one greater, which breaks an assumption in parse_line(), leading to
it writing a NUL byte one byte past the end of the buffer where we
reconstruct the line from the two packets.

It's conceivable that an attacker controlled set of packets could
cause this to zero out the first byte of the "next" pointer of the
grub_mm_region structure following the current_line buffer.

Do not advance the pointer in the split header case.

Fixes: CVE-2022-28734

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/net/http.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/grub-core/net/http.c b/grub-core/net/http.c
index 7dfdb2372e..24a7030edb 100644
--- a/grub-core/net/http.c
+++ b/grub-core/net/http.c
@@ -193,9 +193,7 @@ http_receive (grub_net_tcp_socket_t sock __attribute__ ((unused)),
 	  int have_line = 1;
 	  char *t;
 	  ptr = grub_memchr (nb->data, '\n', nb->tail - nb->data);
-	  if (ptr)
-	    ptr++;
-	  else
+	  if (ptr == NULL)
 	    {
 	      have_line = 0;
 	      ptr = (char *) nb->tail;
-- 
2.34.1