File 0022-net-ip-Do-IP-fragment-maths-safely.patch of Package grub2.28511

From 906dff72b0448106360d46331b16c1305a088c41 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Mon, 20 Dec 2021 19:41:21 +1100
Subject: [PATCH 22/37] net/ip: Do IP fragment maths safely

We can receive packets with invalid IP fragmentation information. This
can lead to rsm->total_len underflowing and becoming very large.

Then, in grub_netbuff_alloc(), we add to this very large number, which can
cause it to overflow and wrap back around to a small positive number.
The allocation then succeeds, but the resulting buffer is too small and
subsequent operations can write past the end of the buffer.

Catch the underflow here.

Fixes: CVE-2022-28733

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/net/ip.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/grub-core/net/ip.c b/grub-core/net/ip.c
index 01410798b3..937be87678 100644
--- a/grub-core/net/ip.c
+++ b/grub-core/net/ip.c
@@ -25,6 +25,7 @@
 #include <grub/net/netbuff.h>
 #include <grub/mm.h>
 #include <grub/priority_queue.h>
+#include <grub/safemath.h>
 #include <grub/time.h>
 
 struct iphdr {
@@ -551,7 +552,14 @@ grub_net_recv_ip4_packets (struct grub_net_buff *nb,
     {
       rsm->total_len = (8 * (grub_be_to_cpu16 (iph->frags) & OFFSET_MASK)
 			+ (nb->tail - nb->data));
-      rsm->total_len -= ((iph->verhdrlen & 0xf) * sizeof (grub_uint32_t));
+
+      if (grub_sub (rsm->total_len, (iph->verhdrlen & 0xf) * sizeof (grub_uint32_t),
+		    &rsm->total_len))
+	{
+	  grub_dprintf ("net", "IP reassembly size underflow\n");
+	  return GRUB_ERR_NONE;
+	}
+
       rsm->asm_netbuff = grub_netbuff_alloc (rsm->total_len);
       if (!rsm->asm_netbuff)
 	{
-- 
2.34.1