129 lines
4.1 KiB
Diff
129 lines
4.1 KiB
Diff
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From 8b8da020f57414c90981371da71fdf32d2253ac7 Mon Sep 17 00:00:00 2001
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From: Martin Jungblut Schreiner <martinjungblut@gmail.com>
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Date: Mon, 29 Dec 2025 19:52:56 -0300
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Subject: [PATCH 1/2] libfdisk: (dos) fix logical partition start
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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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fdisk could accept adjacent logical partitions, causing the EBR for the new
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logical partition to be written inside the previous partition’s data area.
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This can corrupt the EBR chain.
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Fix free-sector search to keep an EBR gap (first_lba) after logical partitions.
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---
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libfdisk/src/dos.c | 15 +++++++++++++++
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1 file changed, 15 insertions(+)
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diff --git a/libfdisk/src/dos.c b/libfdisk/src/dos.c
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index c88d2a4f213..f85104b2828 100644
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--- a/libfdisk/src/dos.c
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+++ b/libfdisk/src/dos.c
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@@ -1201,6 +1201,21 @@ static int find_first_free_sector_in_range(
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p_start -= cxt->first_lba;
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if (first < p_start)
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continue;
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+
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+ /* if we're placing a logical partition start, ensure
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+ there's room for the *next* EBR (stored at start - first_lba).
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+ therefore enforce:
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+ start(Lnew) >= end(Lprev) + first_lba + 1 */
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+ if (logical && first > p_end && (first - p_end) <= cxt->first_lba) {
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+ first = p_end + 1 + cxt->first_lba;
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+ first_moved = 1;
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+
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+ if (first > end)
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+ return -ENOSPC;
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+
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+ continue;
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+ }
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+
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if (first <= p_end) {
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first = p_end + 1 + (logical ? cxt->first_lba : 0);
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first_moved = 1;
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From bf3d4aeec708fae7aa30530a1bf42ee1d35366f8 Mon Sep 17 00:00:00 2001
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From: Martin Jungblut Schreiner <martinjungblut@gmail.com>
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Date: Mon, 29 Dec 2025 20:46:39 -0300
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Subject: [PATCH 2/2] tests: fdisk: add regression test for missing EBR gap
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between logical partitions
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Add a DOS/MBR test case where the first logical partition starts at 6145
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(extended start 2048). In the regressed behaviour fdisk allows the next
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logical partition to start at prev_end+1, which would place its EBR
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(start - 2048) inside the previous logical partition.
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The expected behaviour is to require the next starting sector to be at least
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prev_end + 2048 + 1 (e.g. 790528 in the testcase).
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Closes issue #3925.
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---
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tests/expected/fdisk/mbr-logical-ebr-gap | 15 ++++++++++
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tests/ts/fdisk/mbr-logical-ebr-gap | 35 ++++++++++++++++++++++++
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2 files changed, 50 insertions(+)
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create mode 100644 tests/expected/fdisk/mbr-logical-ebr-gap
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create mode 100755 tests/ts/fdisk/mbr-logical-ebr-gap
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diff --git a/tests/expected/fdisk/mbr-logical-ebr-gap b/tests/expected/fdisk/mbr-logical-ebr-gap
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new file mode 100644
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index 00000000000..c25b9be7a8d
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--- /dev/null
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+++ b/tests/expected/fdisk/mbr-logical-ebr-gap
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@@ -0,0 +1,15 @@
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+
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+---layout----------
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+Disk <removed>: 1 GiB, 1073741824 bytes, 2097152 sectors
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+Units: sectors of 1 * 512 = 512 bytes
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+Sector size (logical/physical): 512 bytes / 512 bytes
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+I/O size (minimum/optimal): 512 bytes / <removed> bytes
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+Disklabel type: dos
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+Disk identifier: <removed>
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+
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+Device Boot Start End Sectors Id Type Start-C/H/S End-C/H/S Attrs
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+<removed>1 2048 2097151 2095104 5 Extended 0/32/33 130/138/8
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+<removed>5 6145 788479 782335 83 Linux 0/97/35 49/20/35
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+<removed>6 2097151 2097151 1 83 Linux 130/138/8 130/138/8
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+-------------------
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+
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diff --git a/tests/ts/fdisk/mbr-logical-ebr-gap b/tests/ts/fdisk/mbr-logical-ebr-gap
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new file mode 100755
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index 00000000000..ffc9f96bc31
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--- /dev/null
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+++ b/tests/ts/fdisk/mbr-logical-ebr-gap
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@@ -0,0 +1,35 @@
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+#!/bin/bash
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+TS_TOPDIR="${0%/*}/../.."
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+TS_DESC="MBR: default start for logical must reserve EBR gap"
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+. "$TS_TOPDIR"/functions.sh
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+ts_init "$*"
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+ts_check_test_command "$TS_CMD_FDISK"
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+
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+# 1GiB image => 2097152 sectors @ 512B
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+TEST_IMAGE_NAME=$(ts_image_init 1024)
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+
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+# key assertion is in the resulting layout: L2 must not start at 788480,
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+# but at 790528 (= 788480 + 2048), leaving room for the EBR.
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+echo -e \
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+"o
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+n
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+e
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+1
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+2048
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+2097151
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+n
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+6145
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+788479
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+n
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+788480
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+2097151
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+w
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+q
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+" | $TS_CMD_FDISK --noauto-pt "$TEST_IMAGE_NAME" &> /dev/null
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+
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+echo -ne "\n---layout----------\n" >> "$TS_OUTPUT"
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+$TS_CMD_FDISK -x "$TEST_IMAGE_NAME" >> "$TS_OUTPUT"
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+echo -ne "-------------------\n\n" >> "$TS_OUTPUT"
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+ts_fdisk_clean "$TEST_IMAGE_NAME"
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+
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+ts_finalize
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