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From d758a667f27b38d9ecc0715062307a8bce741aee Mon Sep 17 00:00:00 2001
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From: "Darrick J. Wong" <darrick.wong@oracle.com>
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Date: Wed, 20 Nov 2019 11:32:55 -0800
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Subject: [PATCH 06/10] tune2fs: prohibit toggling uninit_bg on live
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filesystems
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An internal customer followed an erroneous AskUbuntu article[1] to try to
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change the UUID of a live ext4 filesystem. The article claims that you
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can work around tune2fs' "cannot change UUID on live fs" error by
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disabling uninit_bg, changing the UUID, and re-enabling the feature.
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This led to metadata corruption because tune2fs' journal descriptor
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rewrite races with regular filesystem writes. Therefore, prevent
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administrators from turning on or off uninit_bg on a mounted fs.
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[1] https://askubuntu.com/questions/132079/how-do-i-change-uuid-of-a-disk-to-whatever-i-want/195839#459097
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Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
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Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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---
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misc/tune2fs.c | 12 ++++++++++++
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1 file changed, 12 insertions(+)
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diff --git a/misc/tune2fs.c b/misc/tune2fs.c
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index 7d2d38d7..301cf388 100644
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--- a/misc/tune2fs.c
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+++ b/misc/tune2fs.c
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@@ -1308,6 +1308,12 @@ mmp_error:
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if (FEATURE_ON(E2P_FEATURE_RO_INCOMPAT,
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EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
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+ if (mount_flags & EXT2_MF_MOUNTED) {
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+ fputs(_("Cannot enable uninit_bg on a mounted "
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+ "filesystem!\n"), stderr);
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+ exit(1);
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+ }
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+
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/* Do not enable uninit_bg when metadata_csum enabled */
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if (ext2fs_has_feature_metadata_csum(fs->super))
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ext2fs_clear_feature_gdt_csum(fs->super);
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@@ -1317,6 +1323,12 @@ mmp_error:
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if (FEATURE_OFF(E2P_FEATURE_RO_INCOMPAT,
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EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
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+ if (mount_flags & EXT2_MF_MOUNTED) {
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+ fputs(_("Cannot disable uninit_bg on a mounted "
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+ "filesystem!\n"), stderr);
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+ exit(1);
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+ }
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+
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err = disable_uninit_bg(fs,
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EXT4_FEATURE_RO_COMPAT_GDT_CSUM);
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if (err)
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--
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2.21.1
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