[PATCH 05/24] devtmpfs: open code ksys_chdir and ksys_chroot
From: Christoph Hellwig <hch@lst.de>
Date: 2020-07-21 16:28:32
Also in:
linux-fsdevel, linux-raid, lkml
Subsystem:
driver core, kobjects, debugfs and sysfs, the rest · Maintainers:
Greg Kroah-Hartman, "Rafael J. Wysocki", Danilo Krummrich, Linus Torvalds
devtmpfs is the only non-early init caller of ksys_chdir and ksys_chroot with kernel pointers. Just open code the two operations which only really need a single path lookup anyway in devtmpfs_setup instead. The open coded verson doesn't need any of the stale dentry revalidation logic from the full blown version as those can't happen on tmpfs and ramfs. Signed-off-by: Christoph Hellwig <hch@lst.de> --- drivers/base/devtmpfs.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 5e8d677ee783bc..f798d3976b4052 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c@@ -25,6 +25,7 @@ #include <linux/sched.h> #include <linux/slab.h> #include <linux/kthread.h> +#include <linux/fs_struct.h> #include <uapi/linux/mount.h> #include "base.h"
@@ -393,6 +394,7 @@ static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid, static int devtmpfs_setup(void *p) { + struct path path; int err; err = ksys_unshare(CLONE_NEWNS);
@@ -401,8 +403,16 @@ static int devtmpfs_setup(void *p) err = devtmpfs_do_mount("/"); if (err) goto out; - ksys_chdir("/.."); /* will traverse into overmounted root */ - ksys_chroot("."); + + /* traverse into overmounted root and then chroot to it */ + if (!kern_path("/..", LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path) && + !inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR) && + ns_capable(current_user_ns(), CAP_SYS_CHROOT) && + !security_path_chroot(&path)) { + set_fs_pwd(current->fs, &path); + set_fs_root(current->fs, &path); + } + path_put(&path); out: *(int *)p = err; complete(&setup_done);
--
2.27.0