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From fb66f40ba67b88408a43cb38492053985bfe4968 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Tue, 18 Jan 2022 14:29:20 +1100
Subject: net/tftp: Avoid a trivial UAF
Under tftp errors, we print a tftp error message from the tftp header.
However, the tftph pointer is a pointer inside nb, the netbuff. Previously,
we were freeing the nb and then dereferencing it. Don't do that, use it
and then free it later.
This isn't really _bad_ per se, especially as we're single-threaded, but
it trips up fuzzers.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/net/tftp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/grub-core/net/tftp.c b/grub-core/net/tftp.c
index d1afa2535..4222d93b6 100644
--- a/grub-core/net/tftp.c
+++ b/grub-core/net/tftp.c
@@ -251,9 +251,9 @@ tftp_receive (grub_net_udp_socket_t sock __attribute__ ((unused)),
return GRUB_ERR_NONE;
case TFTP_ERROR:
data->have_oack = 1;
- grub_netbuff_free (nb);
grub_error (GRUB_ERR_IO, "%s", tftph->u.err.errmsg);
grub_error_save (&data->save_err);
+ grub_netbuff_free (nb);
return GRUB_ERR_NONE;
default:
grub_netbuff_free (nb);
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