[PATCH v2 20/28] open: handle fsid mappings

Christian Brauner
2020-02-14T18:41:51Z

Let chown_common() lookup fsids in the fsid mappings. If no fsid mappings are
setup the behavior is unchanged, i.e. fsids are looked up in the id mappings.
do_faccessat() just needs to translate from real ids into fsids.

Filesystems that share a superblock in all user namespaces they are mounted in
will retain their old semantics even with the introduction of fsidmappings.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
- Christian Brauner <christian.brauner@ubuntu.com>:
- handle faccessat() too
---
fs/open.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 0788b3715731..4e092845728f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -32,6 +32,7 @@
#include <linux/ima.h>
#include <linux/dnotify.h>
#include <linux/compat.h>
+#include <linux/fsuidgid.h>

#include "internal.h"

@@ -361,8 +362,10 @@ long do_faccessat(int dfd, const char __user *filename, int mode)
if (!override_cred)
return -ENOMEM;

- override_cred->fsuid = override_cred->uid;
- override_cred->fsgid = override_cred->gid;
+ override_cred->kfsuid = override_cred->uid;
+ override_cred->kfsgid = override_cred->gid;
+ override_cred->fsuid = kuid_to_kfsuid(override_cred->user_ns, override_cred->uid);
+ override_cred->fsgid = kgid_to_kfsgid(override_cred->user_ns, override_cred->gid);

if (!issecure(SECURE_NO_SETUID_FIXUP)) {
/* Clear the capabilities if we switch to a non-root user */
@@ -626,8 +629,13 @@ static int chown_common(const struct path *path, uid_t user, gid_t group)
kuid_t uid;
kgid_t gid;

- uid = make_kuid(current_user_ns(), user);
- gid = make_kgid(current_user_ns(), group);
+ if (is_userns_visible(inode->i_sb->s_iflags)) {
+ uid = make_kuid(current_user_ns(), user);
+ gid = make_kgid(current_user_ns(), group);
+ } else {
+ uid = make_kfsuid(current_user_ns(), user);
+ gid = make_kfsgid(current_user_ns(), group);
+ }

retry_deleg:
newattrs.ia_valid = ATTR_CTIME;
--
2.25.0