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

[Wolfgang Bumiller]

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,