fs/adfs: super: fix use-after-free bug

BugLink: https://bugs.launchpad.net/bugs/1840289

[ Upstream commit 5808b14a ]

Fix a use-after-free bug during filesystem initialisation, where we
access the disc record (which is stored in a buffer) after we have
released the buffer.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

fs/adfs/super.c

@@ -368,6 +368,7 @@ static int adfs_fill_super(struct super_block *sb, void *data, int silent)
 	struct buffer_head *bh;
 	struct object_info root_obj;
 	unsigned char *b_data;
+	unsigned int blocksize;
 	struct adfs_sb_info *asb;
 	struct inode *root;
 	int ret = -EINVAL;
@@ -419,8 +420,10 @@ static int adfs_fill_super(struct super_block *sb, void *data, int silent)
 		goto error_free_bh;
 	}
 
+	blocksize = 1 << dr->log2secsize;
 	brelse(bh);
-	if (sb_set_blocksize(sb, 1 << dr->log2secsize)) {
+
+	if (sb_set_blocksize(sb, blocksize)) {
 		bh = sb_bread(sb, ADFS_DISCRECORD / sb->s_blocksize);
 		if (!bh) {
 			adfs_error(sb, "couldn't read superblock on "