[PATCH] ext4: cache es->s_journal_inum in ext4_sb_info

[Ojaswin Mujoo]

Currently, we access journal ino through sbi->s_es->s_journal_inum,
which directly reads from the ext4 sb buffer head. If someone modifies
this underneath us then the s_journal_inum field might get corrupted.

Although direct block device modifications can be expected to cause
issues in the FS, let's cache s_journal_inum in sbi->s_journal_ino so
our checks can be more resillient.

Suggested-by: Baokun Li <libaokun1@xxxxxxxxxx>
Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
---
 fs/ext4/block_validity.c | 23 ++++++++++++++++-------
 fs/ext4/ext4.h           |  1 +
 fs/ext4/inode.c          | 19 +++++++++++++++----
 fs/ext4/super.c          |  5 ++++-
 4 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
index 87ee3a17bd29..54e6f3499263 100644
--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -247,9 +247,9 @@ int ext4_setup_system_zone(struct super_block *sb)
 		if (ret)
 			goto err;
 	}
-	if (ext4_has_feature_journal(sb) && sbi->s_es->s_journal_inum) {
+	if (ext4_has_feature_journal(sb) && sbi->s_journal_ino) {
 		ret = ext4_protect_reserved_inode(sb, system_blks,
-				le32_to_cpu(sbi->s_es->s_journal_inum));
+						  sbi->s_journal_ino);
 		if (ret)
 			goto err;
 	}
@@ -351,11 +351,20 @@ int ext4_check_blockref(const char *function, unsigned int line,
 {
 	__le32 *bref = p;
 	unsigned int blk;
-
-	if (ext4_has_feature_journal(inode->i_sb) &&
-	    (inode->i_ino ==
-	     le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum)))
-		return 0;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+
+	if (ext4_has_feature_journal(inode->i_sb)) {
+		/* If we are called from journal init path then
+		 * sbi->s_journal_ino would be 0
+		 */
+		u32 journal_ino = sbi->s_journal_ino ?
+					  sbi->s_journal_ino :
+					  sbi->s_es->s_journal_inum;
+		WARN_ON_ONCE(journal_ino == 0);
+
+		if (inode->i_ino == journal_ino)
+			return 0;
+	}
 
 	while (bref < p+max) {
 		blk = le32_to_cpu(*bref++);
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 2b7d781bfcad..648b0459e9fd 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1556,6 +1556,7 @@ struct ext4_sb_info {
 	u32 s_max_batch_time;
 	u32 s_min_batch_time;
 	struct file *s_journal_bdev_file;
+	u32 s_journal_ino;
 #ifdef CONFIG_QUOTA
 	/* Names of quota files with journalled quota */
 	char __rcu *s_qf_names[EXT4_MAXQUOTAS];
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 365d31004bd0..50961bc0c94d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -384,10 +384,21 @@ static int __check_block_validity(struct inode *inode, const char *func,
 				unsigned int line,
 				struct ext4_map_blocks *map)
 {
-	if (ext4_has_feature_journal(inode->i_sb) &&
-	    (inode->i_ino ==
-	     le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum)))
-		return 0;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+
+	if (ext4_has_feature_journal(inode->i_sb)) {
+		/*
+		 * If we are called from journal init path then
+		 * sbi->s_journal_ino would be 0
+		 */
+		u32 journal_ino = sbi->s_journal_ino ?
+					  sbi->s_journal_ino :
+					  sbi->s_es->s_journal_inum;
+		WARN_ON_ONCE(journal_ino == 0);
+
+		if (inode->i_ino == journal_ino)
+			return 0;
+	}
 	if (!ext4_inode_block_valid(inode, map->m_pblk, map->m_len)) {
 		ext4_error_inode(inode, func, line, map->m_pblk,
 				 "lblock %lu mapped to illegal pblock %llu "
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a963ffda692a..44e79db7f12a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4162,7 +4162,8 @@ int ext4_calculate_overhead(struct super_block *sb)
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_super_block *es = sbi->s_es;
 	struct inode *j_inode;
-	unsigned int j_blocks, j_inum = le32_to_cpu(es->s_journal_inum);
+	unsigned int j_blocks;
+	u32 j_inum = sbi->s_journal_ino;
 	ext4_group_t i, ngroups = ext4_get_groups_count(sb);
 	ext4_fsblk_t overhead = 0;
 	char *buf = (char *) get_zeroed_page(GFP_NOFS);
@@ -6091,6 +6092,8 @@ static int ext4_load_journal(struct super_block *sb,
 		ext4_commit_super(sb);
 	}
 
+	EXT4_SB(sb)->s_journal_ino = le32_to_cpu(es->s_journal_inum);
+
 	return 0;
 
 err_out:
-- 
2.48.1