commit: dccfafea4e8b4622a7527a764d581ac0123b107e
Author: Felix Bier <Felix.Bier <AT> rohde-schwarz <DOT> com>
AuthorDate: Mon Nov 9 19:36:33 2020 +0000
Commit: Matt Turner <mattst88 <AT> gentoo <DOT> org>
CommitDate: Sat Nov 14 16:34:57 2020 +0000
URL: https://gitweb.gentoo.org/proj/catalyst.git/commit/?id=dccfafea
catalyst: Restore root and cwd after exiting mount namespace
This commit saves the file descriptor of /proc/self/{root,cwd}
before entering into the new mount namespace. When restoring the
previous mount namespace, it restores /proc/self/{root,cwd}
based on the saved file descriptors.
Without this change, catalyst cannot be run in a chroot when
using the recent changes regarding mount namespaces: After the
mount namespace has been exited, /proc/self/root points to the "/"
of the host system, not the "/" of the chroot. Therefore, the
cleanup phase of catalyst runs outside of the chroot.
The code is similar to how nsenter(1) sets root and cwd:
https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/tree/sys-utils/nsenter.c#n452
Tested in a Gentoo chroot and in Gentoo VM (non-chroot).
Signed-off-by: Felix Bier <felix.bier <AT> rohde-schwarz.com>
Signed-off-by: Matt Turner <mattst88 <AT> gentoo.org>
catalyst/context.py | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/catalyst/context.py b/catalyst/context.py
index 8a58f33d..01a6d930 100644
--- a/catalyst/context.py
+++ b/catalyst/context.py
@@ -16,11 +16,21 @@ def namespace(mount=False, uts=False, ipc=False, net=False,
pid=False,
(user, "user"): None,
}
+ dirs = {
+ "root": None,
+ "cwd": None,
+ }
+
# Save fds of current namespaces
for ns in [ns for ns in namespaces if ns[0]]:
fp = open(f"/proc/self/ns/{ns[1]}")
namespaces[ns] = fp
+ # Save fds of current directories
+ if mount:
+ for d in dirs:
+ dirs[d] = os.open(f"/proc/self/{d}", os.O_RDONLY)
+
simple_unshare(mount=mount, uts=uts, ipc=ipc, net=net, pid=pid, user=user,
hostname=hostname)
try:
@@ -30,3 +40,15 @@ def namespace(mount=False, uts=False, ipc=False, net=False,
pid=False,
fp = namespaces[ns]
setns(fp.fileno(), 0)
fp.close()
+
+ if mount:
+ # Restore original root and cwd. Since we cannot directly chroot to
+ # a fd, first change the current directory to the fd of the
+ # original root, then chroot to "."
+
+ os.fchdir(dirs["root"])
+ os.chroot(".")
+ os.fchdir(dirs["cwd"])
+
+ for fd in dirs.values():
+ os.close(fd)
