[PATCH proxmox-backup v3] fix #5247: relative paths in exclude patterns.

[Manuel Federanko <m.federanko@proxmox.com>]

Patterns which start with ./ or for that matter contain /../ or similar
constructs will never match, since they get compared to sanitized paths
from directory traversal, sanitize those patterns too. Implement this
for both .pxarexclude files and the --exclude command line option. Log
a warning if a path was sanitized.

Signed-off-by: Manuel Federanko <m.federanko@proxmox.com>
Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=5247
---
changed since v2:
  - log a warning for the cli option and the exclude files
  - simplify trailing slash detection
changed since v1:
  - inline normalize_lexically helper
  - bump log level from info to warn

 pbs-client/src/pxar/create.rs     | 14 +++++++++++++-
 pbs-client/src/pxar/tools.rs      | 29 +++++++++++++++++++++++++++++
 proxmox-backup-client/src/main.rs | 16 ++++++++++++++--
 3 files changed, 56 insertions(+), 3 deletions(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index 70b858092..b8fc94ab6 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -589,7 +589,19 @@ impl Archiver {
                 (line, MatchType::Exclude, false)
             };
 
-            match MatchEntry::parse_pattern(line, PatternFlag::PATH_NAME, mode) {
+            let line = OsStr::from_bytes(line);
+            let line_normalized = crate::pxar::tools::normalize_lexically(line);
+            if line_normalized.as_os_str() != line {
+                warn!(
+                    "Sanitized exclude pattern. Exclude patterns are relative to the current backup root, \
+                    not the current working directory and should not contain '.' or '..' as path segments"
+                );
+            }
+            match MatchEntry::parse_pattern(
+                line_normalized.as_path().as_os_str().as_bytes(),
+                PatternFlag::PATH_NAME,
+                mode,
+            ) {
                 Ok(pattern) => {
                     if anchored {
                         self.patterns.push(pattern.add_flags(MatchFlag::ANCHORED));
diff --git a/pbs-client/src/pxar/tools.rs b/pbs-client/src/pxar/tools.rs
index 475c08ad3..28f66801b 100644
--- a/pbs-client/src/pxar/tools.rs
+++ b/pbs-client/src/pxar/tools.rs
@@ -76,6 +76,35 @@ fn assert_single_path_component_do(path: &Path) -> Result<(), Error> {
     Ok(())
 }
 
+pub fn normalize_lexically<S: AsRef<OsStr> + ?Sized>(path: &S) -> PathBuf {
+    // FIXME: Once std::path::normalize_lexically is stabilized we can
+    // switch to that
+    use std::path::Component;
+
+    let path = Path::new(path);
+    let has_trailing_slash = path
+        .as_os_str()
+        .as_encoded_bytes()
+        .ends_with(std::path::MAIN_SEPARATOR_STR.as_bytes());
+    let mut new = PathBuf::new();
+    let iter = path.components();
+    for component in iter {
+        match component {
+            Component::RootDir => new.push(Component::RootDir),
+            Component::Prefix(p) => new.push(Component::Prefix(p)),
+            Component::CurDir => continue,
+            Component::ParentDir => {
+                new.pop();
+            }
+            Component::Normal(n) => new.push(n),
+        };
+    }
+    if has_trailing_slash {
+        new.push("");
+    }
+    new
+}
+
 #[rustfmt::skip]
 fn symbolic_mode(c: u64, special: bool, special_x: u8, special_no_x: u8) -> [u8; 3] {
     [
diff --git a/proxmox-backup-client/src/main.rs b/proxmox-backup-client/src/main.rs
index a1533b79b..fd8d6a61a 100644
--- a/proxmox-backup-client/src/main.rs
+++ b/proxmox-backup-client/src/main.rs
@@ -842,9 +842,21 @@ async fn create_backup(
         let entry = entry
             .as_str()
             .ok_or_else(|| format_err!("Invalid pattern string slice"))?;
+        let entry_normalized = pbs_client::pxar::tools::normalize_lexically(entry);
+        if entry_normalized.as_os_str() != entry {
+            log::warn!(
+                "Sanitized exclude pattern. Exclude patterns are relative to backup root, \
+                not the current working directory and should not contain '.' or '..' as path \
+                segments"
+            );
+        }
         pattern_list.push(
-            MatchEntry::parse_pattern(entry, PatternFlag::PATH_NAME, MatchType::Exclude)
-                .map_err(|err| format_err!("invalid exclude pattern entry: {}", err))?,
+            MatchEntry::parse_pattern(
+                entry_normalized.as_os_str().as_encoded_bytes(),
+                PatternFlag::PATH_NAME,
+                MatchType::Exclude,
+            )
+            .map_err(|err| format_err!("invalid exclude pattern entry: {}", err))?,
         );
     }
 
-- 
2.47.3