ext4: fix warning in ext4_handle_inode_extension

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix warning in ext4_handle_inode_extension

We got issue as follows:

EXT4-fs error (device loop0) in ext4_reserve_inode_write:5741: Out of memory

EXT4-fs error (device loop0): ext4_setattr:5462: inode #13: comm syz-executor.0: mark_inode_dirty error

EXT4-fs error (device loop0) in ext4_setattr:5519: Out of memory

EXT4-fs error (device loop0): ext4_ind_map_blocks:595: inode #13: comm syz-executor.0: Can't allocate blocks for non-extent mapped inodes with bigalloc

------------[ cut here ]------------

WARNING: CPU: 1 PID: 4361 at fs/ext4/file.c:301 ext4_file_write_iter+0x11c9/0x1220

Modules linked in:

CPU: 1 PID: 4361 Comm: syz-executor.0 Not tainted 5.10.0+ #1

RIP: 0010:ext4_file_write_iter+0x11c9/0x1220

RSP: 0018:ffff924d80b27c00 EFLAGS: 00010282

RAX: ffffffff815a3379 RBX: 0000000000000000 RCX: 000000003b000000

RDX: ffff924d81601000 RSI: 00000000000009cc RDI: 00000000000009cd

RBP: 000000000000000d R08: ffffffffbc5a2c6b R09: 0000902e0e52a96f

R10: ffff902e2b7c1b40 R11: ffff902e2b7c1b40 R12: 000000000000000a

R13: 0000000000000001 R14: ffff902e0e52aa10 R15: ffffffffffffff8b

FS: 00007f81a7f65700(0000) GS:ffff902e3bc80000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffffffff600400 CR3: 000000012db88001 CR4: 00000000003706e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

do_iter_readv_writev+0x2e5/0x360

do_iter_write+0x112/0x4c0

do_pwritev+0x1e5/0x390

__x64_sys_pwritev2+0x7e/0xa0

do_syscall_64+0x37/0x50

entry_SYSCALL_64_after_hwframe+0x44/0xa9

Above issue may happen as follows:

Assume

inode.i_size=4096

EXT4_I(inode)->i_disksize=4096

step 1: set inode->i_isize = 8192

ext4_setattr

if (attr->ia_size != inode->i_size)

EXT4_I(inode)->i_disksize = attr->ia_size;

rc = ext4_mark_inode_dirty

ext4_reserve_inode_write

ext4_get_inode_loc

__ext4_get_inode_loc

sb_getblk --> return -ENOMEM

...

if (!error) ->will not update i_size

i_size_write(inode, attr->ia_size);

Now:

inode.i_size=4096

EXT4_I(inode)->i_disksize=8192

step 2: Direct write 4096 bytes

ext4_file_write_iter

ext4_dio_write_iter

iomap_dio_rw ->return error

if (extend)

ext4_handle_inode_extension

WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize);

->Then trigger warning.

To solve above issue, if mark inode dirty failed in ext4_setattr just

set 'EXT4_I(inode)->i_disksize' with old value.