From: Christian Brauner <christian.brauner@ubuntu.com>
Date: Thu, 29 Jul 2021 12:32:21 +0000 (+0200)
Subject: conf: add and use mount_beneath_fd()
X-Git-Tag: lxc-5.0.0~130^2~2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c146c54eee43525a1bb92ec40d5a5a2009410d50;p=thirdparty%2Flxc.git

conf: add and use mount_beneath_fd()

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---

diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 65c7be762..f8402b561 100644
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -1784,7 +1784,7 @@ static int lxc_finalize_devpts_child(struct lxc_handler *handler)
 
 		for (ret = -1, opts = mntopt_sets; opts && *opts; opts++) {
 			/* mount new devpts instance */
-			ret = mount("devpts", "/dev/pts", "devpts", MS_NOSUID | MS_NOEXEC, *opts);
+			ret = mount_beneath_fd(rootfs->dfd_dev, "", "pts", "devpts", MS_NOSUID | MS_NOEXEC, *opts);
 			if (ret == 0)
 				break;
 		}
@@ -1817,7 +1817,7 @@ static int lxc_finalize_devpts_child(struct lxc_handler *handler)
 	DEBUG("Created \"/dev/ptmx\" file as bind mount target");
 
 	/* Main option: use a bind-mount to please AppArmor  */
-	ret = mount("/dev/pts/ptmx", "/dev/ptmx", NULL, MS_BIND, NULL);
+	ret = mount_beneath_fd(rootfs->dfd_dev, "pts/ptmx", "ptmx", NULL, MS_BIND, NULL);
 	if (!ret)
 		return log_debug(0, "Bind mounted \"/dev/pts/ptmx\" to \"/dev/ptmx\"");
 	else
diff --git a/src/lxc/mount_utils.c b/src/lxc/mount_utils.c
index b8aadaea6..1cf71dadd 100644
--- a/src/lxc/mount_utils.c
+++ b/src/lxc/mount_utils.c
@@ -11,6 +11,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 
+#include "conf.h"
 #include "file_utils.h"
 #include "log.h"
 #include "macro.h"
@@ -604,3 +605,33 @@ bool can_use_bind_mounts(void)
 
 	return supported == 1;
 }
+
+int mount_beneath_fd(int fd, const char *source, const char *target,
+		     const char *fs_name, unsigned int flags, const void *data)
+{
+	int ret;
+	char buf_source[PATH_MAX], buf_target[PATH_MAX];
+
+	if (abspath(source) || abspath(target))
+		return ret_errno(EINVAL);
+
+	ret = strnprintf(buf_target, sizeof(buf_target), "/proc/self/fd/%d/%s", fd, target);
+	if (ret < 0)
+		return syserror("Failed to create path");
+
+	if (is_empty_string(source)) {
+		ret = mount(fs_name ?: "", buf_target, fs_name, flags, data);
+	} else {
+		ret = strnprintf(buf_source, sizeof(buf_source), "/proc/self/fd/%d/%s", fd, source);
+		if (ret < 0)
+			return syserror("Failed to create path");
+
+		source = buf_source;
+		ret = mount(source, buf_target, fs_name, flags, data);
+	}
+	if (ret < 0)
+		return syserror("Failed to mount \"%s\" to \"%s\"", source, buf_target);
+
+	TRACE("Mounted \"%s\" to \"%s\"", source, buf_target);
+	return 0;
+}
diff --git a/src/lxc/mount_utils.h b/src/lxc/mount_utils.h
index dcc786f28..17ff4698f 100644
--- a/src/lxc/mount_utils.h
+++ b/src/lxc/mount_utils.h
@@ -12,6 +12,8 @@
 #include "memory_utils.h"
 #include "syscall_wrappers.h"
 
+struct lxc_rootfs;
+
 /* open_tree() flags */
 
 #ifndef AT_RECURSIVE
@@ -189,7 +191,6 @@ __hidden extern int fd_bind_mount(int dfd_from, const char *path_from,
 				  int dfd_to, const char *path_to,
 				  __u64 o_flags_to, __u64 resolve_flags_to,
 				  unsigned int attr_flags, bool recursive);
-
 __hidden extern int fd_mount_idmapped(int dfd_from, const char *path_from,
 				      __u64 o_flags_from, __u64 resolve_flags_from,
 				      int dfd_to, const char *path_to,
@@ -220,5 +221,8 @@ __hidden extern unsigned long add_required_remount_flags(const char *s,
 
 __hidden extern bool can_use_mount_api(void);
 __hidden extern bool can_use_bind_mounts(void);
+__hidden extern int mount_beneath_fd(int fd, const char *source,
+				     const char *target, const char *fs_name,
+				     unsigned int flags, const void *data);
 
 #endif /* __LXC_MOUNT_UTILS_H */