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| author | Suraj Jitindar Singh <surajjs@amazon.com> | 2020-02-18 19:08:51 -0800 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2020-02-21 19:31:46 -0500 |
| commit | 7c990728b99ed6fbe9c75fc202fce1172d9916da (patch) | |
| tree | 73fcf3b46fb35781ab76a4c8fb84be7f70f87c96 /fs/ext4/resize.c | |
| parent | df3da4ea5a0fc5d115c90d5aa6caa4dd433750a7 (diff) | |
| download | linux-7c990728b99ed6fbe9c75fc202fce1172d9916da.tar.gz | |
ext4: fix potential race between s_flex_groups online resizing and access
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
Diffstat (limited to 'fs/ext4/resize.c')
| -rw-r--r-- | fs/ext4/resize.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c index 536cc9f3809143..a50b51270ea9ad 100644 --- a/fs/ext4/resize.c +++ b/fs/ext4/resize.c @@ -1430,11 +1430,14 @@ static void ext4_update_super(struct super_block *sb, percpu_counter_read(&sbi->s_freeclusters_counter)); if (ext4_has_feature_flex_bg(sb) && sbi->s_log_groups_per_flex) { ext4_group_t flex_group; + struct flex_groups *fg; + flex_group = ext4_flex_group(sbi, group_data[0].group); + fg = sbi_array_rcu_deref(sbi, s_flex_groups, flex_group); atomic64_add(EXT4_NUM_B2C(sbi, free_blocks), - &sbi->s_flex_groups[flex_group].free_clusters); + &fg->free_clusters); atomic_add(EXT4_INODES_PER_GROUP(sb) * flex_gd->count, - &sbi->s_flex_groups[flex_group].free_inodes); + &fg->free_inodes); } /* |