Re: [PATCH v2 1/4] ext4: fix out of bounds punch offset

[Baokun Li <libaokun1@huawei.com>]

On 2025/5/6 9:20, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
>
> 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.
>
> Fixes: 982bf37da09d ("ext4: refactor ext4_punch_hole()")
> Reported-by: Liebes Wang <wanghaichi0403@gmail.com>
> Closes: https://lore.kernel.org/linux-ext4/ac3a58f6-e686-488b-a9ee-fc041024e43d@huawei.com/
> Tested-by: Liebes Wang <wanghaichi0403@gmail.com>
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
Looks good to me.

Reviewed-by: Baokun Li <libaokun1@huawei.com>
> ---
>   fs/ext4/inode.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 94c7d2d828a6..4ec4a80b6879 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4016,7 +4016,7 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>   	WARN_ON_ONCE(!inode_is_locked(inode));
>   
>   	/* No need to punch hole beyond i_size */
> -	if (offset >= inode->i_size)
> +	if (offset >= inode->i_size || offset >= max_end)
>   		return 0;
>   
>   	/*