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From 852a0a22d674b0594aecf0912a0885d197f34978 Mon Sep 17 00:00:00 2001
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From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Date: Tue, 5 May 2020 16:35:57 +0100
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Subject: [PATCH 6/9] virtiofsd: jail lo->proc_self_fd
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RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
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Message-id: <20200505163600.22956-5-dgilbert@redhat.com>
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Patchwork-id: 96275
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O-Subject: [RHEL-AV-8.2.1 qemu-kvm PATCH 4/7] virtiofsd: jail lo->proc_self_fd
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Bugzilla: 1817445
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>
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From: Miklos Szeredi <mszeredi@redhat.com>
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While it's not possible to escape the proc filesystem through
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lo->proc_self_fd, it is possible to escape to the root of the proc
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filesystem itself through "../..".
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Use a temporary mount for opening lo->proc_self_fd, that has it's root at
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/proc/self/fd/, preventing access to the ancestor directories.
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Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
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Message-Id: <20200429124733.22488-1-mszeredi@redhat.com>
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Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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(cherry picked from commit 397ae982f4df46e7d4b2625c431062c9146f3b83)
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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tools/virtiofsd/passthrough_ll.c | 27 +++++++++++++++++++++++++--
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1 file changed, 25 insertions(+), 2 deletions(-)
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diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
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index 184ad0f..73d8405 100644
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--- a/tools/virtiofsd/passthrough_ll.c
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+++ b/tools/virtiofsd/passthrough_ll.c
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@@ -2540,6 +2540,8 @@ static void print_capabilities(void)
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static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
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{
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pid_t child;
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+ char template[] = "virtiofsd-XXXXXX";
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+ char *tmpdir;
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/*
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* Create a new pid namespace for *child* processes. We'll have to
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@@ -2601,12 +2603,33 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
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exit(1);
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}
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+ tmpdir = mkdtemp(template);
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+ if (!tmpdir) {
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+ fuse_log(FUSE_LOG_ERR, "tmpdir(%s): %m\n", template);
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+ exit(1);
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+ }
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+
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+ if (mount("/proc/self/fd", tmpdir, NULL, MS_BIND, NULL) < 0) {
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+ fuse_log(FUSE_LOG_ERR, "mount(/proc/self/fd, %s, MS_BIND): %m\n",
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+ tmpdir);
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+ exit(1);
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+ }
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+
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/* Now we can get our /proc/self/fd directory file descriptor */
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- lo->proc_self_fd = open("/proc/self/fd", O_PATH);
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+ lo->proc_self_fd = open(tmpdir, O_PATH);
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if (lo->proc_self_fd == -1) {
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- fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
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+ fuse_log(FUSE_LOG_ERR, "open(%s, O_PATH): %m\n", tmpdir);
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exit(1);
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}
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+
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+ if (umount2(tmpdir, MNT_DETACH) < 0) {
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+ fuse_log(FUSE_LOG_ERR, "umount2(%s, MNT_DETACH): %m\n", tmpdir);
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+ exit(1);
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+ }
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+
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+ if (rmdir(tmpdir) < 0) {
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+ fuse_log(FUSE_LOG_ERR, "rmdir(%s): %m\n", tmpdir);
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+ }
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}
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/*
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--
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1.8.3.1
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