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ext4: fix potential race between s_flex_groups online resizing and access

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During an online resize an array of s_flex_groups structures gets replaced
so it can get enlarged. If there is a concurrent access to the array and
this memory has been reused then this can lead to an invalid memory access.

The s_flex_group array has been converted into an array of pointers rather
than an array of structures. This is to ensure that the information
contained in the structures cannot get out of sync during a resize due to
an accessor updating the value in the old structure after it has been
copied but before the array pointer is updated. Since the structures them-
selves are no longer copied but only the pointers to them this case is
mitigated.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206443
Link: https://lore.kernel.org/r/20200221053458.730016-4-tytso@mit.edu
Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
This commit is contained in:
Suraj Jitindar Singh
2020-02-18 19:08:51 -08:00
committed by Theodore Ts'o
parent df3da4ea5a
commit 7c990728b9
5 changed files with 76 additions and 37 deletions
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9
fs/ext4/mballoc.c
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@@ -3038,7 +3038,8 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
ext4_group_t flex_group = ext4_flex_group(sbi,
ac->ac_b_ex.fe_group);
atomic64_sub(ac->ac_b_ex.fe_len,
&sbi->s_flex_groups[flex_group].free_clusters);
&sbi_array_rcu_deref(sbi, s_flex_groups,
flex_group)->free_clusters);
}
err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
@@ -4936,7 +4937,8 @@ do_more:
if (sbi->s_log_groups_per_flex) {
ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
atomic64_add(count_clusters,
&sbi->s_flex_groups[flex_group].free_clusters);
&sbi_array_rcu_deref(sbi, s_flex_groups,
flex_group)->free_clusters);
}
/*
@@ -5093,7 +5095,8 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
if (sbi->s_log_groups_per_flex) {
ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
atomic64_add(clusters_freed,
&sbi->s_flex_groups[flex_group].free_clusters);
&sbi_array_rcu_deref(sbi, s_flex_groups,
flex_group)->free_clusters);
}
ext4_mb_unload_buddy(&e4b);