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

[Filip Schauer]

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