f2fs: fix to truncate first page in error path of f2fs_truncate()

syzbot reports a bug as below:

loop0: detected capacity change from 0 to 40427
F2FS-fs (loop0): Wrong SSA boundary, start(3584) end(4096) blocks(3072)
F2FS-fs (loop0): Can't find valid F2FS filesystem in 1th superblock
F2FS-fs (loop0): invalid crc value
F2FS-fs (loop0): f2fs_convert_inline_folio: corrupted inline inode ino=3, i_addr[0]:0x1601, run fsck to fix.
------------[ cut here ]------------
kernel BUG at fs/inode.c:753!
RIP: 0010:clear_inode+0x169/0x190 fs/inode.c:753
Call Trace:
 <TASK>
 evict+0x504/0x9c0 fs/inode.c:810
 f2fs_fill_super+0x5612/0x6fa0 fs/f2fs/super.c:5047
 get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1692
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
 do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
 do_mount fs/namespace.c:4136 [inline]
 __do_sys_mount fs/namespace.c:4347 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4324
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

During f2fs_evict_inode(), clear_inode() detects that we missed to truncate
all page cache before destorying inode, that is because in below path, we
will create page #0 in cache, but missed to drop it in error path, let's fix
it.

- evict
 - f2fs_evict_inode
  - f2fs_truncate
   - f2fs_convert_inline_inode
    - f2fs_grab_cache_folio
    : create page #0 in cache
    - f2fs_convert_inline_folio
    : sanity check failed, return -EFSCORRUPTED
  - clear_inode detects that inode->i_data.nrpages is not zero

Fixes: 92dffd0 ("f2fs: convert inline_data when i_size becomes large")
Reported-by: syzbot+90266696fe5daacebd35@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/68c09802.050a0220.3c6139.000e.GAE@google.com
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/file.c

@@ -904,8 +904,16 @@ int f2fs_truncate(struct inode *inode)
 	/* we should check inline_data size */
 	if (!f2fs_may_inline_data(inode)) {
 		err = f2fs_convert_inline_inode(inode);
-		if (err)
+		if (err) {
+			/*
+			 * Always truncate page #0 to avoid page cache
+			 * leak in evict() path.
+			 */
+			truncate_inode_pages_range(inode->i_mapping,
+					F2FS_BLK_TO_BYTES(0),
+					F2FS_BLK_END_BYTES(0));
 			return err;
+		}
 	}
 
 	err = f2fs_truncate_blocks(inode, i_size_read(inode), true);