jbd2: fix portability problems caused by unaligned accesses

This commit applies the e2fsck/recovery.c portions of commit
1e0c8ca7c08a ("e2fsck: fix portability problems caused by unaligned
accesses) from the e2fsprogs git tree.

The on-disk format for the ext4 journal can have unaigned 32-bit
integers.  This can happen when replaying a journal using a obsolete
checksum format (which was never popularly used, since the v3 format
replaced v2 while the metadata checksum feature was being stablized).

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/jbd2/recovery.c

@@ -196,7 +196,7 @@ static int jbd2_descriptor_block_csum_verify(journal_t *j, void *buf)
 static int count_tags(journal_t *journal, struct buffer_head *bh)
 {
 	char *			tagp;
-	journal_block_tag_t *	tag;
+	journal_block_tag_t	tag;
 	int			nr = 0, size = journal->j_blocksize;
 	int			tag_bytes = journal_tag_bytes(journal);
 
@@ -206,14 +206,14 @@ static int count_tags(journal_t *journal, struct buffer_head *bh)
 	tagp = &bh->b_data[sizeof(journal_header_t)];
 
 	while ((tagp - bh->b_data + tag_bytes) <= size) {
-		tag = (journal_block_tag_t *) tagp;
+		memcpy(&tag, tagp, sizeof(tag));
 
 		nr++;
 		tagp += tag_bytes;
-		if (!(tag->t_flags & cpu_to_be16(JBD2_FLAG_SAME_UUID)))
+		if (!(tag.t_flags & cpu_to_be16(JBD2_FLAG_SAME_UUID)))
 			tagp += 16;
 
-		if (tag->t_flags & cpu_to_be16(JBD2_FLAG_LAST_TAG))
+		if (tag.t_flags & cpu_to_be16(JBD2_FLAG_LAST_TAG))
 			break;
 	}
 
@@ -433,9 +433,9 @@ static int jbd2_commit_block_csum_verify(journal_t *j, void *buf)
 }
 
 static int jbd2_block_tag_csum_verify(journal_t *j, journal_block_tag_t *tag,
+				      journal_block_tag3_t *tag3,
 				      void *buf, __u32 sequence)
 {
-	journal_block_tag3_t *tag3 = (journal_block_tag3_t *)tag;
 	__u32 csum32;
 	__be32 seq;
 
@@ -496,7 +496,7 @@ static int do_one_pass(journal_t *journal,
 	while (1) {
 		int			flags;
 		char *			tagp;
-		journal_block_tag_t *	tag;
+		journal_block_tag_t	tag;
 		struct buffer_head *	obh;
 		struct buffer_head *	nbh;
 
@@ -613,8 +613,8 @@ static int do_one_pass(journal_t *journal,
 			       <= journal->j_blocksize - descr_csum_size) {
 				unsigned long io_block;
 
-				tag = (journal_block_tag_t *) tagp;
-				flags = be16_to_cpu(tag->t_flags);
+				memcpy(&tag, tagp, sizeof(tag));
+				flags = be16_to_cpu(tag.t_flags);
 
 				io_block = next_log_block++;
 				wrap(journal, next_log_block);
@@ -632,7 +632,7 @@ static int do_one_pass(journal_t *journal,
 
 					J_ASSERT(obh != NULL);
 					blocknr = read_tag_block(journal,
-								 tag);
+								 &tag);
 
 					/* If the block has been
 					 * revoked, then we're all done
@@ -647,8 +647,8 @@ static int do_one_pass(journal_t *journal,
 
 					/* Look for block corruption */
 					if (!jbd2_block_tag_csum_verify(
-						journal, tag, obh->b_data,
-						be32_to_cpu(tmp->h_sequence))) {
+			journal, &tag, (journal_block_tag3_t *)tagp,
+			obh->b_data, be32_to_cpu(tmp->h_sequence))) {
 						brelse(obh);
 						success = -EFSBADCRC;
 						printk(KERN_ERR "JBD2: Invalid "