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

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Date:   Sun, 25 Aug 2019 22:56:12 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     "zhangyi (F)" <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, jack@...e.cz, adilger.kernel@...ger.ca
Subject: Re: [PATCH v5] ext4: fix potential use after free in system zone via
 remount with noblock_validity

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,

     				  	       	     - Ted