[PATCH container] fix #7667: prevent stale errno from breaking device passthrough

[PATCH container] fix #7667: prevent stale errno from breaking device passthrough

[Filip Schauer]

Since a successful stat() call does not reset $!, unconditionally
checking it afterward can cause a false error when $! was set earlier.

This causes device passthrough to always fail with "Device $path does
not exist" for privileged containers with an ostype that doesn't have a
matching config in /usr/share/lxc/config/<ostype>.common.conf.

Fix this by checking $! only when stat() actually fails. Also switch to
the $!{ENOENT} syntax, allowing the POSIX ENOENT import to be dropped.

Signed-off-by: Filip Schauer <f.schauer@proxmox.com>
---
 src/PVE/LXC/Tools.pm | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/PVE/LXC/Tools.pm b/src/PVE/LXC/Tools.pm
index 40dd270..ce2467e 100644
--- a/src/PVE/LXC/Tools.pm
+++ b/src/PVE/LXC/Tools.pm
@@ -4,7 +4,7 @@ package PVE::LXC::Tools;
 use strict;
 use warnings;
 
-use POSIX qw(ENOENT S_ISBLK S_ISCHR);
+use POSIX qw(S_ISBLK S_ISCHR);
 
 use PVE::SafeSyslog;
 
@@ -159,9 +159,8 @@ sub get_device_mode_and_rdev($) {
 
     die "Path is not defined\n" if !defined($path);
 
-    my ($mode, $rdev) = (stat($path))[2, 6];
-    die "Device $path does not exist\n" if $! == ENOENT;
-    die "Error accessing device $path\n" if !defined($mode) || !defined($rdev);
+    my ($mode, $rdev) = (stat($path))[2, 6]
+        or die($!{ENOENT} ? "Device $path does not exist\n" : "Error accessing device $path: $!\n");
     die "$path is not a device\n" if !S_ISBLK($mode) && !S_ISCHR($mode);
 
     return ($mode, $rdev);
-- 
2.47.3