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- Add --bind-fd and --ro-bind-fd to let you bind a O_PATH fd.

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eabdullin 2024-09-05 08:05:53 +03:00
parent 1a72f13f01
commit 1722c3e51c
2 changed files with 128 additions and 2 deletions
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119
SOURCES/0001-Add-bind-fd-and-ro-bind-fd-to-let-you-bind-a-O_PATH-.patch Normal file
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@ -0,0 +1,119 @@
From 52d5f7c3ba5c8e10b3a992304fd28cd4d18caeeb Mon Sep 17 00:00:00 2001
From: Alexander Larsson <alexl@redhat.com>
Date: Tue, 18 Jun 2024 10:20:36 +0200
Subject: [PATCH] Add --bind-fd and --ro-bind-fd to let you bind a O_PATH fd.
This is useful for example if you for some reason don't have the real
path. It is also a way to make bind-mounts race-free (i.e. to have the
mount actually be the thing you wanted to be mounted, avoiding issues
where some other process replaces the target in parallel with the bwrap
launch.
Unfortunately due to some technical details we can't actually directly
mount the dirfd, as they come from different user namespace which is not
permitted, but at least we can delay resolving the fd to a path as much as
possible, and then validate after mount that we actually mounted the right
thing.
Signed-off-by: Alexander Larsson <alexl@redhat.com>
(cherry picked from commit a253257cd298892da43e15201d83f9a02c9b58b5)
[kalev: Backport to 0.4.x]
Signed-off-by: Kalev Lember <klember@redhat.com>
---
bubblewrap.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++
tests/test-run.sh | 7 ++++++-
2 files changed, 56 insertions(+), 1 deletion(-)
diff --git a/bubblewrap.c b/bubblewrap.c
index b3d52bc..38b3646 100644
--- a/bubblewrap.c
+++ b/bubblewrap.c
@@ -250,6 +250,8 @@ usage (int ecode, FILE *out)
" --dev-bind-try SRC DEST Equal to --dev-bind but ignores non-existent SRC\n"
" --ro-bind SRC DEST Bind mount the host path SRC readonly on DEST\n"
" --ro-bind-try SRC DEST Equal to --ro-bind but ignores non-existent SRC\n"
+ " --bind-fd FD DEST Bind open directory or path fd on DEST\n"
+ " --ro-bind-fd FD DEST Bind open directory or path fd read-only on DEST\n"
" --remount-ro DEST Remount DEST as readonly; does not recursively remount\n"
" --exec-label LABEL Exec label for the sandbox\n"
" --file-label LABEL File label for temporary sandbox content\n"
@@ -1106,6 +1108,30 @@ setup_newroot (bool unshare_pid,
(op->type == SETUP_RO_BIND_MOUNT ? BIND_READONLY : 0) |
(op->type == SETUP_DEV_BIND_MOUNT ? BIND_DEVICES : 0),
source, dest);
+
+ if (op->fd >= 0)
+ {
+ struct stat fd_st, mount_st;
+
+ /* When using bind-fd, there is a race condition between resolving the fd as a magic symlink
+ * and mounting it, where someone could replace what is at the symlink target. Ideally
+ * we would not even resolve the symlink and directly bind-mount from the fd, but unfortunately
+ * we can't do that, because its not permitted to bind mount a fd from another user namespace.
+ * So, we resolve, mount and then compare fstat+stat to detect the race. */
+
+ if (fstat(op->fd, &fd_st) != 0)
+ die_with_error("Can't stat fd %d", op->fd);
+ if (lstat(dest, &mount_st) != 0)
+ die_with_error("Can't stat mount at %s", dest);
+
+ if (fd_st.st_ino != mount_st.st_ino ||
+ fd_st.st_dev != mount_st.st_dev)
+ die_with_error("Race condition binding dirfd");
+
+ close(op->fd);
+ op->fd = -1;
+ }
+
break;
case SETUP_REMOUNT_RO_NO_RECURSIVE:
@@ -1643,6 +1669,30 @@ parse_args_recurse (int *argcp,
if (strcmp(arg, "--dev-bind-try") == 0)
op->flags = ALLOW_NOTEXIST;
+ argv += 2;
+ argc -= 2;
+ }
+ else if (strcmp (arg, "--bind-fd") == 0 ||
+ strcmp (arg, "--ro-bind-fd") == 0)
+ {
+ int src_fd;
+ char *endptr;
+
+ if (argc < 3)
+ die ("--bind-fd takes two arguments");
+
+ src_fd = strtol (argv[1], &endptr, 10);
+ if (argv[1][0] == 0 || endptr[0] != 0 || src_fd < 0)
+ die ("Invalid fd: %s", argv[1]);
+
+ if (strcmp(arg, "--ro-bind-fd") == 0)
+ op = setup_op_new (SETUP_RO_BIND_MOUNT);
+ else
+ op = setup_op_new (SETUP_BIND_MOUNT);
+ op->source = xasprintf ("/proc/self/fd/%d", src_fd);
+ op->fd = src_fd;
+ op->dest = argv[2];
+
argv += 2;
argc -= 2;
}
diff --git a/tests/test-run.sh b/tests/test-run.sh
index 702c480..ce1eaf6 100755
--- a/tests/test-run.sh
+++ b/tests/test-run.sh
@@ -375,5 +375,10 @@ else
echo "ok - Test --pidns"
fi
+echo "foobar" > file-data
+$RUN --proc /proc --dev /dev --bind / / --bind-fd 100 /tmp cat /tmp/file-data 100< . > stdout
+assert_file_has_content stdout foobar
+
+echo "ok - bind-fd"
echo "ok - End of test"
--
2.46.0

11
SPECS/bubblewrap.spec
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@ -1,6 +1,6 @@
Name: bubblewrap
Version: 0.4.1
Release: 6%{?dist}
Release: 7%{?dist}.alma.1
Summary: Core execution tool for unprivileged containers
License: LGPLv2+
@ -9,6 +9,10 @@ URL: https://github.com/projectatomic/bubblewrap
Source0: https://github.com/projectatomic/bubblewrap/releases/download/v%{version}/bubblewrap-%{version}.tar.xz
Patch0: 0001-Avoid-memory-leak-if-args-is-specified-multiple-time.patch
# Patches were taken from:
# https://gitlab.com/redhat/centos-stream/rpms/bubblewrap/-/commit/60adf0819cf8199b62484f08e4e9f9d55e35fa03
Patch1: 0001-Add-bind-fd-and-ro-bind-fd-to-let-you-bind-a-O_PATH-.patch
BuildRequires: autoconf automake libtool
BuildRequires: gcc
BuildRequires: libcap-devel
@ -23,7 +27,7 @@ containers that works as a setuid binary on kernels without
user namespaces.
%prep
%autosetup
%autosetup -p1
%build
if ! test -x configure; then NOCONFIGURE=1 ./autogen.sh; fi
@ -47,6 +51,9 @@ find %{buildroot} -name '*.la' -delete -print
%{_mandir}/man1/*
%changelog
* Thu Sep 05 2024 Eduard Abdullin <eabdullin@almalinux.org> - 0.4.1-7.alma.1
- Add --bind-fd and --ro-bind-fd to let you bind a O_PATH fd.
* Mon Aug 09 2021 Mohan Boddu <mboddu@redhat.com> - 0.4.1-6
- Rebuilt for IMA sigs, glibc 2.34, aarch64 flags
Related: rhbz#1991688