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From: Wolfgang Bumiller <w.bumiller@proxmox.com>
To: Filip Schauer <f.schauer@proxmox.com>
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Subject: Re: [pbs-devel] [PATCH backup] fix #5946: disks: wipe: ensure GPT
header backup is wiped
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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@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,
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