Re: [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity

zhangyi (F)
2019-08-26T08:31:47Z

On 2019/8/26 10:56, Theodore Y. Ts'o Wrote:
> I added a missing rcu_read_lock() to prevent a suspicious RCU
> warning when CONFIG_PROVE_RCU is enabled:
>
> diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
> index 003dc1dc2da3..f7bc914a74df 100644
> --- a/fs/ext4/block_validity.c
> +++ b/fs/ext4/block_validity.c
> @@ -330,11 +330,13 @@ void ext4_release_system_zone(struct super_block *sb)
> {
> struct ext4_system_blocks *system_blks;
>
> + rcu_read_lock();
> system_blks = rcu_dereference(EXT4_SB(sb)->system_blks);
> rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);
>
> if (system_blks)
> call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
> + rcu_read_unlock();
> }
>
> int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk,
>

Hi Ted，
Sorry about missing this warning, I think switch to use:
system_blks = rcu_dereference_raw(EXT4_SB(sb)->system_blks);
or
system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, true);
is enough to fix this waring, am I missing something?

Thanks,
Yi.