ext4: fix out of bounds punch offset

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

ext4: fix out of bounds punch offset

Punching a hole with a start offset that exceeds max_end is not

permitted and will result in a negative length in the

truncate_inode_partial_folio() function while truncating the page cache,

potentially leading to undesirable consequences.

A simple reproducer:

truncate -s 9895604649994 /mnt/foo

xfs_io -c "pwrite 8796093022208 4096" /mnt/foo

xfs_io -c "fpunch 8796093022213 25769803777" /mnt/foo

kernel BUG at include/linux/highmem.h:275!

Oops: invalid opcode: 0000 [#1] SMP PTI

CPU: 3 UID: 0 PID: 710 Comm: xfs_io Not tainted 6.15.0-rc3

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-2.fc40 04/01/2014

RIP: 0010:zero_user_segments.constprop.0+0xd7/0x110

RSP: 0018:ffffc90001cf3b38 EFLAGS: 00010287

RAX: 0000000000000005 RBX: ffffea0001485e40 RCX: 0000000000001000

RDX: 000000000040b000 RSI: 0000000000000005 RDI: 000000000040b000

RBP: 000000000040affb R08: ffff888000000000 R09: ffffea0000000000

R10: 0000000000000003 R11: 00000000fffc7fc5 R12: 0000000000000005

R13: 000000000040affb R14: ffffea0001485e40 R15: ffff888031cd3000

FS: 00007f4f63d0b780(0000) GS:ffff8880d337d000(0000)

knlGS:0000000000000000

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

CR2: 000000001ae0b038 CR3: 00000000536aa000 CR4: 00000000000006f0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

<TASK>

truncate_inode_partial_folio+0x3dd/0x620

truncate_inode_pages_range+0x226/0x720

? bdev_getblk+0x52/0x3e0

? ext4_get_group_desc+0x78/0x150

? crc32c_arch+0xfd/0x180

? __ext4_get_inode_loc+0x18c/0x840

? ext4_inode_csum+0x117/0x160

? jbd2_journal_dirty_metadata+0x61/0x390

? __ext4_handle_dirty_metadata+0xa0/0x2b0

? kmem_cache_free+0x90/0x5a0

? jbd2_journal_stop+0x1d5/0x550

? __ext4_journal_stop+0x49/0x100

truncate_pagecache_range+0x50/0x80

ext4_truncate_page_cache_block_range+0x57/0x3a0

ext4_punch_hole+0x1fe/0x670

ext4_fallocate+0x792/0x17d0

? __count_memcg_events+0x175/0x2a0

vfs_fallocate+0x121/0x560

ksys_fallocate+0x51/0xc0

__x64_sys_fallocate+0x24/0x40

x64_sys_call+0x18d2/0x4170

do_syscall_64+0xa7/0x220

entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fix this by filtering out cases where the punching start offset exceeds

max_end.