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Date: Tue, 27 Aug 2019 17:20:40 +0800 From: "zhangyi (F)" <yi.zhang@...wei.com> To: Jan Kara <jack@...e.cz> CC: "Theodore Y. Ts'o" <tytso@....edu>, <linux-ext4@...r.kernel.org>, <adilger.kernel@...ger.ca> Subject: Re: [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity On 2019/8/26 23:03, Jan Kara Wrote: > On Mon 26-08-19 16:31:41, zhangyi (F) wrote: >> 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? > > Proper fix for this is actually using: > > system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, > lockdep_is_held(&sb->s_umount)); > Totally agree, will resend the patch. Thanks, Yi.
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