f2fs: fix to truncate preallocated blocks in f2fs_file_open()

chenyuwen reports a f2fs bug as below:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000011
 fscrypt_set_bio_crypt_ctx+0x78/0x1e8
 f2fs_grab_read_bio+0x78/0x208
 f2fs_submit_page_read+0x44/0x154
 f2fs_get_read_data_page+0x288/0x5f4
 f2fs_get_lock_data_page+0x60/0x190
 truncate_partial_data_page+0x108/0x4fc
 f2fs_do_truncate_blocks+0x344/0x5f0
 f2fs_truncate_blocks+0x6c/0x134
 f2fs_truncate+0xd8/0x200
 f2fs_iget+0x20c/0x5ac
 do_garbage_collect+0x5d0/0xf6c
 f2fs_gc+0x22c/0x6a4
 f2fs_disable_checkpoint+0xc8/0x310
 f2fs_fill_super+0x14bc/0x1764
 mount_bdev+0x1b4/0x21c
 f2fs_mount+0x20/0x30
 legacy_get_tree+0x50/0xbc
 vfs_get_tree+0x5c/0x1b0
 do_new_mount+0x298/0x4cc
 path_mount+0x33c/0x5fc
 __arm64_sys_mount+0xcc/0x15c
 invoke_syscall+0x60/0x150
 el0_svc_common+0xb8/0xf8
 do_el0_svc+0x28/0xa0
 el0_svc+0x24/0x84
 el0t_64_sync_handler+0x88/0xec

It is because inode.i_crypt_info is not initialized during below path:
- mount
 - f2fs_fill_super
  - f2fs_disable_checkpoint
   - f2fs_gc
    - f2fs_iget
     - f2fs_truncate

So, let's relocate truncation of preallocated blocks to f2fs_file_open(),
after fscrypt_file_open().

Fixes: d4dd19e ("f2fs: do not expose unwritten blocks to user by DIO")
Reported-by: chenyuwen <[email protected]>
Closes: https://lore.kernel.org/linux-kernel/[email protected]
Signed-off-by: Chao Yu <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>

Author: chaseyu

fs/f2fs/f2fs.h

@@ -803,6 +803,7 @@ enum {
 	FI_COW_FILE,		/* indicate COW file */
 	FI_ATOMIC_COMMITTED,	/* indicate atomic commit completed except disk sync */
 	FI_ATOMIC_REPLACE,	/* indicate atomic replace */
+	FI_OPENED_FILE,		/* indicate file has been opened */
 	FI_MAX,			/* max flag, never be used */
 };
 

fs/f2fs/file.c

@@ -554,6 +554,42 @@ static int f2fs_file_mmap(struct file *file, struct vm_area_struct *vma)
 	return 0;
 }
 
+static int finish_preallocate_blocks(struct inode *inode)
+{
+	int ret;
+
+	inode_lock(inode);
+	if (is_inode_flag_set(inode, FI_OPENED_FILE)) {
+		inode_unlock(inode);
+		return 0;
+	}
+
+	if (!file_should_truncate(inode)) {
+		set_inode_flag(inode, FI_OPENED_FILE);
+		inode_unlock(inode);
+		return 0;
+	}
+
+	f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+	filemap_invalidate_lock(inode->i_mapping);
+
+	truncate_setsize(inode, i_size_read(inode));
+	ret = f2fs_truncate(inode);
+
+	filemap_invalidate_unlock(inode->i_mapping);
+	f2fs_up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
+
+	if (!ret)
+		set_inode_flag(inode, FI_OPENED_FILE);
+
+	inode_unlock(inode);
+	if (ret)
+		return ret;
+
+	file_dont_truncate(inode);
+	return 0;
+}
+
 static int f2fs_file_open(struct inode *inode, struct file *filp)
 {
 	int err = fscrypt_file_open(inode, filp);
@@ -571,7 +607,11 @@ static int f2fs_file_open(struct inode *inode, struct file *filp)
 	filp->f_mode |= FMODE_NOWAIT;
 	filp->f_mode |= FMODE_CAN_ODIRECT;
 
-	return dquot_file_open(inode, filp);
+	err = dquot_file_open(inode, filp);
+	if (err)
+		return err;
+
+	return finish_preallocate_blocks(inode);
 }
 
 void f2fs_truncate_data_blocks_range(struct dnode_of_data *dn, int count)

fs/f2fs/inode.c

@@ -613,14 +613,6 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
 	}
 	f2fs_set_inode_flags(inode);
 
-	if (file_should_truncate(inode) &&
-			!is_sbi_flag_set(sbi, SBI_POR_DOING)) {
-		ret = f2fs_truncate(inode);
-		if (ret)
-			goto bad_inode;
-		file_dont_truncate(inode);
-	}
-
 	unlock_new_inode(inode);
 	trace_f2fs_iget(inode);
 	return inode;