From fe4abbda80eea7f65b6b5cc544a806fb6e064917 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@redhat.com>
Date: Thu, 18 Nov 2021 12:57:32 +0100
Subject: [PATCH 2/3] hw/block/fdc: Prevent end-of-track overrun
 (CVE-2021-3507)
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RH-Author: Jon Maloy <jmaloy@redhat.com>
RH-MergeRequest: 194: hw/block/fdc: Prevent end-of-track overrun (CVE-2021-3507)
RH-Commit: [1/2] 31fa0351382b4ca5bd989b09e4d811ae73040673 (jmaloy/qemu-kvm)
RH-Bugzilla: 1951521
RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
RH-Acked-by: Thomas Huth <thuth@redhat.com>
RH-Acked-by: Hanna Reitz <hreitz@redhat.com>

Per the 82078 datasheet, if the end-of-track (EOT byte in
the FIFO) is more than the number of sectors per side, the
command is terminated unsuccessfully:

* 5.2.5 DATA TRANSFER TERMINATION

  The 82078 supports terminal count explicitly through
  the TC pin and implicitly through the underrun/over-
  run and end-of-track (EOT) functions. For full sector
  transfers, the EOT parameter can define the last
  sector to be transferred in a single or multisector
  transfer. If the last sector to be transferred is a par-
  tial sector, the host can stop transferring the data in
  mid-sector, and the 82078 will continue to complete
  the sector as if a hardware TC was received. The
  only difference between these implicit functions and
  TC is that they return "abnormal termination" result
  status. Such status indications can be ignored if they
  were expected.

* 6.1.3 READ TRACK

  This command terminates when the EOT specified
  number of sectors have been read. If the 82078
  does not find an I D Address Mark on the diskette
  after the second· occurrence of a pulse on the
  INDX# pin, then it sets the IC code in Status Regis-
  ter 0 to "01" (Abnormal termination), sets the MA bit
  in Status Register 1 to "1", and terminates the com-
  mand.

* 6.1.6 VERIFY

  Refer to Table 6-6 and Table 6-7 for information
  concerning the values of MT and EC versus SC and
  EOT value.

* Table 6·6. Result Phase Table

* Table 6-7. Verify Command Result Phase Table

Fix by aborting the transfer when EOT > # Sectors Per Side.

Cc: qemu-stable@nongnu.org
Cc: Hervé Poussineau <hpoussin@reactos.org>
Fixes: baca51faff0 ("floppy driver: disk geometry auto detect")
Reported-by: Alexander Bulekov <alxndr@bu.edu>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/339
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211118115733.4038610-2-philmd@redhat.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit defac5e2fbddf8423a354ff0454283a2115e1367)
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
---
 hw/block/fdc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index 97fa6de423..755a26c114 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -1531,6 +1531,14 @@ static void fdctrl_start_transfer(FDCtrl *fdctrl, int direction)
         int tmp;
         fdctrl->data_len = 128 << (fdctrl->fifo[5] > 7 ? 7 : fdctrl->fifo[5]);
         tmp = (fdctrl->fifo[6] - ks + 1);
+        if (tmp < 0) {
+            FLOPPY_DPRINTF("invalid EOT: %d\n", tmp);
+            fdctrl_stop_transfer(fdctrl, FD_SR0_ABNTERM, FD_SR1_MA, 0x00);
+            fdctrl->fifo[3] = kt;
+            fdctrl->fifo[4] = kh;
+            fdctrl->fifo[5] = ks;
+            return;
+        }
         if (fdctrl->fifo[0] & 0x80)
             tmp += fdctrl->fifo[6];
         fdctrl->data_len *= tmp;
-- 
2.35.3