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agent: do not follow link when mounting container proc and sysfs

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Attackers might use it to explore other containers in the same pod.
While it is still safe to allow it, we can just close the race window
like runc does.

Fixes: #885
Signed-off-by: Peng Tao <bergwolf@hyper.sh>
This commit is contained in:
Peng Tao 2020-10-09 12:04:48 +08:00
parent 367e436ff8
commit b7147edadb
1 changed files with 15 additions and 0 deletions
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15
src/agent/rustjail/src/mount.rs
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@ -205,6 +205,21 @@ pub fn init_rootfs(
check_proc_mount(m)?;
}
// If the destination already exists and is not a directory, we bail
// out This is to avoid mounting through a symlink or similar -- which
// has been a "fun" attack scenario in the past.
if m.r#type == "proc" || m.r#type == "sysfs" {
if let Ok(meta) = fs::symlink_metadata(&m.destination) {
if !meta.is_dir() {
return Err(anyhow!(
"Mount point {} must be ordinary directory: got {:?}",
m.destination,
meta.file_type()
));
}
}
}
mount_from(cfd_log, &m, &rootfs, flags, &data, "")?;
// bind mount won't change mount options, we need remount to make mount options
// effective.