fs: Call d_automount with the filesystems creds
BugLink: http://bugs.launchpad.net/bugs/1612135 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: 6e4eab57 ("fs: Add user namespace member to struct super_block") Tested-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> (backported from commit aeaa4a79) Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: Stefan Bader <stefan.bader@canonical.com> Acked-by: Colin King <colin.king@canonical.com> Acked-by: Brad Figg <brad.figg@canonical.com> Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
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