f2fs: fix to avoid updating zero-sized extent in extent cache

As syzbot reported:

F2FS-fs (loop0): __update_extent_tree_range: extent len is zero, type: 0, extent [0, 0, 0], age [0, 0]
------------[ cut here ]------------
kernel BUG at fs/f2fs/extent_cache.c:678!
Oops: invalid opcode: 0000 [CachyOS#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5336 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:__update_extent_tree_range+0x13bc/0x1500 fs/f2fs/extent_cache.c:678
Call Trace:
 <TASK>
 f2fs_update_read_extent_cache_range+0x192/0x3e0 fs/f2fs/extent_cache.c:1085
 f2fs_do_zero_range fs/f2fs/file.c:1657 [inline]
 f2fs_zero_range+0x10c1/0x1580 fs/f2fs/file.c:1737
 f2fs_fallocate+0x583/0x990 fs/f2fs/file.c:2030
 vfs_fallocate+0x669/0x7e0 fs/open.c:342
 ioctl_preallocate fs/ioctl.c:289 [inline]
 file_ioctl+0x611/0x780 fs/ioctl.c:-1
 do_vfs_ioctl+0xb33/0x1430 fs/ioctl.c:576
 __do_sys_ioctl fs/ioctl.c:595 [inline]
 __se_sys_ioctl+0x82/0x170 fs/ioctl.c:583
 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
RIP: 0033:0x7f07bc58eec9

In error path of f2fs_zero_range(), it may add a zero-sized extent
into extent cache, it should be avoided.

Fixes: 6e96194 ("f2fs: support in batch fzero in dnode page")
Cc: stable@kernel.org
Reported-by: syzbot+24124df3170c3638b35f@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-f2fs-devel/68e5d698.050a0220.256323.0032.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

@@ -1654,8 +1654,11 @@ static int f2fs_do_zero_range(struct dnode_of_data *dn, pgoff_t start,
 		f2fs_set_data_blkaddr(dn, NEW_ADDR);
 	}
 
-	f2fs_update_read_extent_cache_range(dn, start, 0, index - start);
-	f2fs_update_age_extent_cache_range(dn, start, index - start);
+	if (index > start) {
+		f2fs_update_read_extent_cache_range(dn, start, 0,
+							index - start);
+		f2fs_update_age_extent_cache_range(dn, start, index - start);
+	}
 
 	return ret;
 }