From aeaa4a79ff6a5ed912b7362f206cf8576fca538b Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sat, 23 Jul 2016 11:20:44 -0500 Subject: [PATCH] fs: Call d_automount with the filesystems creds Seth Forshee reported a mount regression in nfs autmounts with "fs: Add user namespace member to struct super_block". It turns out that the assumption that current->cred is something reasonable during mount while necessary to improve support of unprivileged mounts is wrong in the automount path. To fix the existing filesystems override current->cred with the init_cred before calling d_automount and restore current->cred after d_automount completes. To support unprivileged mounts would require a more nuanced cred selection, so fail on unprivileged mounts for the time being. As none of the filesystems that currently set FS_USERNS_MOUNT implement d_automount this check is only good for preventing future problems. Fixes: 6e4eab577a0c ("fs: Add user namespace member to struct super_block") Tested-by: Seth Forshee Signed-off-by: "Eric W. Biederman" --- fs/namei.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/namei.c b/fs/namei.c index 629823f19a6a..ef573df3297f 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include "internal.h" @@ -1099,6 +1100,7 @@ static int follow_automount(struct path *path, struct nameidata *nd, bool *need_mntput) { struct vfsmount *mnt; + const struct cred *old_cred; int err; if (!path->dentry->d_op || !path->dentry->d_op->d_automount) @@ -1120,11 +1122,16 @@ static int follow_automount(struct path *path, struct nameidata *nd, path->dentry->d_inode) return -EISDIR; + if (path->dentry->d_sb->s_user_ns != &init_user_ns) + return -EACCES; + nd->total_link_count++; if (nd->total_link_count >= 40) return -ELOOP; + old_cred = override_creds(&init_cred); mnt = path->dentry->d_op->d_automount(path); + revert_creds(old_cred); if (IS_ERR(mnt)) { /* * The filesystem is allowed to return -EISDIR here to indicate -- 2.20.1