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authorEric W. Biederman <ebiederm@xmission.com>2017-01-31 20:06:16 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-03-15 05:02:44 +0300
commitd3381fab77cbca6f9664cf49b3f5dd3171f1f6d3 (patch)
tree1b50cb1e44acabab069caf9c03b90dcf2b621877 /fs/autofs4
parent48e2181b0b8d1a1e226b2932a11d6f94aef28fb8 (diff)
downloadlinux-d3381fab77cbca6f9664cf49b3f5dd3171f1f6d3.tar.xz
fs: Better permission checking for submounts
commit 93faccbbfa958a9668d3ab4e30f38dd205cee8d8 upstream. To support unprivileged users mounting filesystems two permission checks have to be performed: a test to see if the user allowed to create a mount in the mount namespace, and a test to see if the user is allowed to access the specified filesystem. The automount case is special in that mounting the original filesystem grants permission to mount the sub-filesystems, to any user who happens to stumble across the their mountpoint and satisfies the ordinary filesystem permission checks. Attempting to handle the automount case by using override_creds almost works. It preserves the idea that permission to mount the original filesystem is permission to mount the sub-filesystem. Unfortunately using override_creds messes up the filesystems ordinary permission checks. Solve this by being explicit that a mount is a submount by introducing vfs_submount, and using it where appropriate. vfs_submount uses a new mount internal mount flags MS_SUBMOUNT, to let sget and friends know that a mount is a submount so they can take appropriate action. sget and sget_userns are modified to not perform any permission checks on submounts. follow_automount is modified to stop using override_creds as that has proven problemantic. do_mount is modified to always remove the new MS_SUBMOUNT flag so that we know userspace will never by able to specify it. autofs4 is modified to stop using current_real_cred that was put in there to handle the previous version of submount permission checking. cifs is modified to pass the mountpoint all of the way down to vfs_submount. debugfs is modified to pass the mountpoint all of the way down to trace_automount by adding a new parameter. To make this change easier a new typedef debugfs_automount_t is introduced to capture the type of the debugfs automount function. Fixes: 069d5ac9ae0d ("autofs: Fix automounts by using current_real_cred()->uid") Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds") Reviewed-by: Trond Myklebust <trond.myklebust@primarydata.com> Reviewed-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/autofs4')
-rw-r--r--fs/autofs4/waitq.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index e44271dfceb6..5db6c8d745ea 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -431,8 +431,8 @@ int autofs4_wait(struct autofs_sb_info *sbi,
memcpy(&wq->name, &qstr, sizeof(struct qstr));
wq->dev = autofs4_get_dev(sbi);
wq->ino = autofs4_get_ino(sbi);
- wq->uid = current_real_cred()->uid;
- wq->gid = current_real_cred()->gid;
+ wq->uid = current_cred()->uid;
+ wq->gid = current_cred()->gid;
wq->pid = pid;
wq->tgid = tgid;
wq->status = -EINTR; /* Status return if interrupted */