[pbs-devel] [PATCH backup] fix #5946: disks: wipe: ensure GPT header backup is wiped

[Filip Schauer]

Superseded by:
https://lore.proxmox.com/pbs-devel/20250211162639.141541-1-f.schauer@proxmox.com/

On 06/02/2025 16:01, Wolfgang Bumiller wrote:
> On Wed, Dec 04, 2024 at 11:33:31AM +0100, Filip Schauer wrote:
>> When wiping a block device with a GUID partition table, the header
>> backup might get left behind at the end of the disk. This commit also
>> wipes the last 4096 bytes of the disk, making sure that a GPT header
>> backup is erased, even from disks with 4k sector sizes.
>>
>> Signed-off-by: Filip Schauer <f.schauer at proxmox.com>
>> ---
>>   src/tools/disks/mod.rs | 47 +++++++++++++++++++++++++-----------------
>>   1 file changed, 28 insertions(+), 19 deletions(-)
>>
>> diff --git a/src/tools/disks/mod.rs b/src/tools/disks/mod.rs
>> index 61aceccd..26e14603 100644
>> --- a/src/tools/disks/mod.rs
>> +++ b/src/tools/disks/mod.rs
>> @@ -1176,29 +1176,38 @@ pub fn wipe_blockdev(disk: &Disk) -> Result<(), Error> {
>>       let wipefs_output = proxmox_sys::command::run_command(wipefs_command, None)?;
>>       info!("wipefs output: {wipefs_output}");
>>   
>> -    let size = disk.size().map(|size| size / 1024 / 1024)?;
>> -    let count = size.min(200);
>> -
>> -    let mut dd_command = std::process::Command::new("dd");
>> -    let mut of_path = OsString::from("of=");
>> -    of_path.push(disk_path);
>> -    let mut count_str = OsString::from("count=");
>> -    count_str.push(count.to_string());
>> -    let args = [
>> -        "if=/dev/zero".into(),
>> -        of_path,
>> -        "bs=1M".into(),
>> -        "conv=fdatasync".into(),
>> -        count_str,
>> -    ];
>> -    dd_command.args(args);
>> -
>> -    let dd_output = proxmox_sys::command::run_command(dd_command, None)?;
>> -    info!("dd output: {dd_output}");
>> +    let dd_zero = |seek: Option<&str>, bs: &str, count: &str| -> Result<(), Error> {
>> +        let mut dd_command = std::process::Command::new("dd");
>> +        let mut of_path = OsString::from("of=");
>> +        of_path.push(disk_path);
>> +        dd_command
>> +            .arg("if=/dev/zero")
>> +            .arg(of_path)
>> +            .arg(format!("bs={bs}"))
>> +            .arg("conv=fdatasync")
>> +            .arg(format!("count={count}"));
>> +
>> +        if let Some(seek) = seek {
>> +            dd_command.arg(format!("seek={seek}"));
>> +        }
>> +
>> +        let dd_output = proxmox_sys::command::run_command(dd_command, None)?;
>> +        info!("dd output: {dd_output}");
>> +
>> +        Ok(())
>> +    };
>> +
>> +    let size = disk.size()?;
>> +    let count = (size / 1024 / 1024).min(200).to_string();
>> +    dd_zero(None, "1M", &count)?;
>>   
>>       if is_partition {
>>           // set the partition type to 0x83 'Linux filesystem'
>>           change_parttype(disk, "8300")?;
>> +    } else {
>> +        // Wipe the end of the disk to remove a potential GPT header backup
>> +        let seek = (size / 512 - 8).to_string();
>> +        dd_zero(Some(&seek), "512", "8")?;
>>       }
>>   
>>       Ok(())
>> -- 
>> 2.39.5
> I don't know why we call out to dd for simple writes.
> I'd suggest just using `write_all_at` like so:
>
> ---8<---
> diff --git a/src/tools/disks/mod.rs b/src/tools/disks/mod.rs
> index 571446db..e22691b7 100644
> --- a/src/tools/disks/mod.rs
> +++ b/src/tools/disks/mod.rs
> @@ -4,11 +4,11 @@ use std::collections::{HashMap, HashSet};
>   use std::ffi::{OsStr, OsString};
>   use std::io;
>   use std::os::unix::ffi::{OsStrExt, OsStringExt};
> -use std::os::unix::fs::MetadataExt;
> +use std::os::unix::fs::{FileExt, MetadataExt, OpenOptionsExt};
>   use std::path::{Path, PathBuf};
>   use std::sync::{Arc, LazyLock};
>   
> -use anyhow::{bail, format_err, Error};
> +use anyhow::{bail, format_err, Context as _, Error};
>   use libc::dev_t;
>   use once_cell::sync::OnceCell;
>   
> @@ -1176,25 +1176,7 @@ pub fn wipe_blockdev(disk: &Disk) -> Result<(), Error> {
>       let wipefs_output = proxmox_sys::command::run_command(wipefs_command, None)?;
>       info!("wipefs output: {wipefs_output}");
>   
> -    let size = disk.size().map(|size| size / 1024 / 1024)?;
> -    let count = size.min(200);
> -
> -    let mut dd_command = std::process::Command::new("dd");
> -    let mut of_path = OsString::from("of=");
> -    of_path.push(disk_path);
> -    let mut count_str = OsString::from("count=");
> -    count_str.push(count.to_string());
> -    let args = [
> -        "if=/dev/zero".into(),
> -        of_path,
> -        "bs=1M".into(),
> -        "conv=fdatasync".into(),
> -        count_str,
> -    ];
> -    dd_command.args(args);
> -
> -    let dd_output = proxmox_sys::command::run_command(dd_command, None)?;
> -    info!("dd output: {dd_output}");
> +    zero_start_and_end(disk)?;
>   
>       if is_partition {
>           // set the partition type to 0x83 'Linux filesystem'
> @@ -1204,6 +1186,29 @@ pub fn wipe_blockdev(disk: &Disk) -> Result<(), Error> {
>       Ok(())
>   }
>   
> +pub fn zero_start_and_end(disk: &Disk) -> Result<(), Error> {
> +    let disk_path = match disk.device_path() {
> +        Some(path) => path,
> +        None => bail!("disk {:?} has no node in /dev", disk.syspath()),
> +    };
> +
> +    let disk_size = disk.size()?;
> +    let file = std::fs::OpenOptions::new()
> +        .write(true)
> +        .custom_flags(libc::O_CLOEXEC | libc::O_DSYNC)
> +        .open(disk_path)
> +        .with_context(|| "failed to open device {disk_path:?} for writing")?;
> +    let write_size = disk_size.min(1024 * 1024);
> +    let zeroes = proxmox_io::boxed::zeroed(write_size as usize);
> +    file.write_all_at(&zeroes, 0)
> +        .with_context(|| "failed to wipe start of device {disk_path:?}")?;
> +    if disk_size > 4096 {
> +        file.write_all_at(&zeroes[0..4096], disk_size - 4096)
> +            .with_context(|| "failed to wipe end of device {disk_path:?}")?;
> +    }
> +    Ok(())
> +}
> +
>   pub fn change_parttype(part_disk: &Disk, part_type: &str) -> Result<(), Error> {
>       let part_path = match part_disk.device_path() {
>           Some(path) => path,