[pbs-devel] [PATCH proxmox-backup] tape/drive/linux_tape: fix and refactor usage of sg-tape-cmd

[Dominik Csapak]

when executing this code as non-root, we use sg-tape-cmd (a setuid binary)
to execute various ioctls on the tape device

we give the command the open tape device fd as stdin, but did not
dup it, so the std::process:Stdio handle closed it on drop,
which let subsequent operation on that file fail (since it was closed)

fix it by dup'ing it before giving it to the command, and also refactor
the calling code, so that we do not forget to do this

Signed-off-by: Dominik Csapak <d.csapak at proxmox.com>
---
 src/tape/drive/linux_tape.rs | 52 ++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 29 deletions(-)

diff --git a/src/tape/drive/linux_tape.rs b/src/tape/drive/linux_tape.rs
index a41b3183..e3c4918c 100644
--- a/src/tape/drive/linux_tape.rs
+++ b/src/tape/drive/linux_tape.rs
@@ -2,7 +2,7 @@
 
 use std::fs::{OpenOptions, File};
 use std::os::unix::fs::OpenOptionsExt;
-use std::os::unix::io::{AsRawFd, FromRawFd};
+use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::convert::TryFrom;
 
 use anyhow::{bail, format_err, Error};
@@ -51,6 +51,17 @@ use crate::{
     }
 };
 
+fn run_sg_tape_cmd(subcmd: &str, args: &[&str], fd: RawFd) -> Result<String, Error> {
+    let mut command = std::process::Command::new(
+        "/usr/lib/x86_64-linux-gnu/proxmox-backup/sg-tape-cmd");
+    command.args(&[subcmd]);
+    command.args(&["--stdin"]);
+    command.args(args);
+    let device_fd = nix::unistd::dup(fd)?;
+    command.stdin(unsafe { std::process::Stdio::from_raw_fd(device_fd)});
+    run_command(command, None)
+}
+
 /// Linux tape drive status
 #[derive(Debug)]
 pub struct LinuxDriveStatus {
@@ -351,12 +362,7 @@ impl LinuxTapeHandle {
             return read_mam_attributes(&mut self.file);
         }
 
-        let mut command = std::process::Command::new(
-            "/usr/lib/x86_64-linux-gnu/proxmox-backup/sg-tape-cmd");
-        command.args(&["cartridge-memory"]);
-        command.args(&["--stdin"]);
-        command.stdin(unsafe { std::process::Stdio::from_raw_fd(self.file.as_raw_fd())});
-        let output = run_command(command, None)?;
+        let output = run_sg_tape_cmd("cartridge-memory", &[], self.file.as_raw_fd())?;
         let result: Result<Vec<MamAttribute>, String> = serde_json::from_str(&output)?;
         result.map_err(|err| format_err!("{}", err))
     }
@@ -371,12 +377,7 @@ impl LinuxTapeHandle {
             return read_volume_statistics(&mut self.file);
         }
 
-        let mut command = std::process::Command::new(
-            "/usr/lib/x86_64-linux-gnu/proxmox-backup/sg-tape-cmd");
-        command.args(&["volume-statistics"]);
-        command.args(&["--stdin"]);
-        command.stdin(unsafe { std::process::Stdio::from_raw_fd(self.file.as_raw_fd())});
-        let output = run_command(command, None)?;
+        let output = run_sg_tape_cmd("volume-statistics", &[], self.file.as_raw_fd())?;
         let result: Result<Lp17VolumeStatistics, String> = serde_json::from_str(&output)?;
         result.map_err(|err| format_err!("{}", err))
     }
@@ -533,12 +534,7 @@ impl TapeDriver for LinuxTapeHandle {
             return read_tape_alert_flags(&mut self.file);
         }
 
-        let mut command = std::process::Command::new(
-            "/usr/lib/x86_64-linux-gnu/proxmox-backup/sg-tape-cmd");
-        command.args(&["tape-alert-flags"]);
-        command.args(&["--stdin"]);
-        command.stdin(unsafe { std::process::Stdio::from_raw_fd(self.file.as_raw_fd())});
-        let output = run_command(command, None)?;
+        let output = run_sg_tape_cmd("tape-alert-flags", &[], self.file.as_raw_fd())?;
         let result: Result<u64, String> = serde_json::from_str(&output)?;
         result
             .map_err(|err| format_err!("{}", err))
@@ -585,17 +581,15 @@ impl TapeDriver for LinuxTapeHandle {
             }
         }
 
-        let mut command = std::process::Command::new(
-            "/usr/lib/x86_64-linux-gnu/proxmox-backup/sg-tape-cmd");
-        command.args(&["encryption"]);
-        if let Some((fingerprint, uuid)) = key_fingerprint {
+        let output = if let Some((fingerprint, uuid)) = key_fingerprint {
             let fingerprint = crate::tools::format::as_fingerprint(fingerprint.bytes());
-            command.args(&["--fingerprint", &fingerprint]);
-            command.args(&["--uuid", &uuid.to_string()]);
-        }
-        command.args(&["--stdin"]);
-        command.stdin(unsafe { std::process::Stdio::from_raw_fd(self.file.as_raw_fd())});
-        let output = run_command(command, None)?;
+            run_sg_tape_cmd("encryption", &[
+                "--fingerprint", &fingerprint,
+                "--uuid", &uuid.to_string(),
+            ], self.file.as_raw_fd())?
+        } else {
+            run_sg_tape_cmd("encryption", &[], self.file.as_raw_fd())?
+        };
         let result: Result<(), String> = serde_json::from_str(&output)?;
         result.map_err(|err| format_err!("{}", err))
     }
-- 
2.20.1