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From fe4abbda80eea7f65b6b5cc544a806fb6e064917 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Philippe=20Mathieu-Daud=C3=A9?= <philmd@redhat.com>
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Date: Thu, 18 Nov 2021 12:57:32 +0100
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Subject: [PATCH 2/3] hw/block/fdc: Prevent end-of-track overrun
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(CVE-2021-3507)
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Jon Maloy <jmaloy@redhat.com>
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RH-MergeRequest: 194: hw/block/fdc: Prevent end-of-track overrun (CVE-2021-3507)
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RH-Commit: [1/2] 31fa0351382b4ca5bd989b09e4d811ae73040673 (jmaloy/qemu-kvm)
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RH-Bugzilla: 1951521
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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RH-Acked-by: Hanna Reitz <hreitz@redhat.com>
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Per the 82078 datasheet, if the end-of-track (EOT byte in
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the FIFO) is more than the number of sectors per side, the
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command is terminated unsuccessfully:
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* 5.2.5 DATA TRANSFER TERMINATION
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The 82078 supports terminal count explicitly through
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the TC pin and implicitly through the underrun/over-
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run and end-of-track (EOT) functions. For full sector
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transfers, the EOT parameter can define the last
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sector to be transferred in a single or multisector
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transfer. If the last sector to be transferred is a par-
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tial sector, the host can stop transferring the data in
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mid-sector, and the 82078 will continue to complete
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the sector as if a hardware TC was received. The
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only difference between these implicit functions and
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TC is that they return "abnormal termination" result
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status. Such status indications can be ignored if they
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were expected.
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* 6.1.3 READ TRACK
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This command terminates when the EOT specified
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number of sectors have been read. If the 82078
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does not find an I D Address Mark on the diskette
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after the second· occurrence of a pulse on the
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INDX# pin, then it sets the IC code in Status Regis-
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ter 0 to "01" (Abnormal termination), sets the MA bit
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in Status Register 1 to "1", and terminates the com-
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mand.
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* 6.1.6 VERIFY
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Refer to Table 6-6 and Table 6-7 for information
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concerning the values of MT and EC versus SC and
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EOT value.
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* Table 6·6. Result Phase Table
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* Table 6-7. Verify Command Result Phase Table
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Fix by aborting the transfer when EOT > # Sectors Per Side.
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Cc: qemu-stable@nongnu.org
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Cc: Hervé Poussineau <hpoussin@reactos.org>
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Fixes: baca51faff0 ("floppy driver: disk geometry auto detect")
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Reported-by: Alexander Bulekov <alxndr@bu.edu>
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Resolves: https://gitlab.com/qemu-project/qemu/-/issues/339
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Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
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Message-Id: <20211118115733.4038610-2-philmd@redhat.com>
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Reviewed-by: Hanna Reitz <hreitz@redhat.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit defac5e2fbddf8423a354ff0454283a2115e1367)
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Signed-off-by: Jon Maloy <jmaloy@redhat.com>
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---
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hw/block/fdc.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/hw/block/fdc.c b/hw/block/fdc.c
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index 97fa6de423..755a26c114 100644
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--- a/hw/block/fdc.c
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+++ b/hw/block/fdc.c
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@@ -1531,6 +1531,14 @@ static void fdctrl_start_transfer(FDCtrl *fdctrl, int direction)
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int tmp;
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fdctrl->data_len = 128 << (fdctrl->fifo[5] > 7 ? 7 : fdctrl->fifo[5]);
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tmp = (fdctrl->fifo[6] - ks + 1);
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+ if (tmp < 0) {
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+ FLOPPY_DPRINTF("invalid EOT: %d\n", tmp);
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+ fdctrl_stop_transfer(fdctrl, FD_SR0_ABNTERM, FD_SR1_MA, 0x00);
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+ fdctrl->fifo[3] = kt;
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+ fdctrl->fifo[4] = kh;
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+ fdctrl->fifo[5] = ks;
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+ return;
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+ }
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if (fdctrl->fifo[0] & 0x80)
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tmp += fdctrl->fifo[6];
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fdctrl->data_len *= tmp;
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--
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2.35.3
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