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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Tue, 18 Jan 2022 14:29:20 +1100
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Subject: [PATCH] net/tftp: Avoid a trivial UAF
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Under tftp errors, we print a tftp error message from the tftp header.
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However, the tftph pointer is a pointer inside nb, the netbuff. Previously,
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we were freeing the nb and then dereferencing it. Don't do that, use it
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and then free it later.
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This isn't really _bad_ per se, especially as we're single-threaded, but
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it trips up fuzzers.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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(cherry picked from commit 956f4329cec23e4375182030ca9b2be631a61ba5)
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(cherry picked from commit dbe9abcdee6ce796811111b67e3f24eefe2135d1)
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(cherry picked from commit 72ae9c5d389d2c0337c44edead6e00db0bb84039)
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---
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grub-core/net/tftp.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/grub-core/net/tftp.c b/grub-core/net/tftp.c
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index 69a9ba6979..09e1511ccf 100644
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--- a/grub-core/net/tftp.c
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+++ b/grub-core/net/tftp.c
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@@ -252,9 +252,9 @@ tftp_receive (grub_net_udp_socket_t sock __attribute__ ((unused)),
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return GRUB_ERR_NONE;
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case TFTP_ERROR:
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data->have_oack = 1;
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- grub_netbuff_free (nb);
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grub_error (GRUB_ERR_IO, "%s", tftph->u.err.errmsg);
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grub_error_save (&data->save_err);
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+ grub_netbuff_free (nb);
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return GRUB_ERR_NONE;
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default:
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grub_netbuff_free (nb);
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