Messages in this thread | | | From | (Eric W. Biederman) | Date | Tue, 28 Jul 2015 13:17:40 -0500 | Subject | Re: [PATCH] user_ns: use correct check for single-threadedness |
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Kees Cook <keescook@chromium.org> writes:
> From: Ricky Zhou <rickyz@chromium.org> > > Checking mm_users > 1 does not mean a process is multithreaded. For > example, reading /proc/PID/maps temporarily increments mm_users, allowing > other processes to (accidentally) interfere with unshare() calls. > > This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly > returning EINVAL if another processes happened to be simultaneously > reading the maps file. > > Signed-off-by: Ricky Zhou <rickyz@chromium.org> > Signed-off-by: Kees Cook <keescook@chromium.org> > Cc: stable@vger.kernel.org
This looks like a good fix. Any chance you can drudge up the commit where this hack came in so that Greg & Company know how far to back port this?
> --- > kernel/fork.c | 4 ++-- > kernel/user_namespace.c | 3 ++- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index dbd9b8d7b7cc..7d138f152dcd 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -75,6 +75,7 @@ > #include <linux/aio.h> > #include <linux/compiler.h> > #include <linux/sysctl.h> > +#include <linux/sched.h> > > #include <asm/pgtable.h> > #include <asm/pgalloc.h> > @@ -1876,8 +1877,7 @@ static int check_unshare_flags(unsigned long unshare_flags) > * needs to unshare vm. > */ > if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) { > - /* FIXME: get_task_mm() increments ->mm_users */ > - if (atomic_read(¤t->mm->mm_users) > 1) > + if (!current_is_single_threaded()) > return -EINVAL; > } > > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c > index 4109f8320684..7e0e021e4304 100644 > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -22,6 +22,7 @@ > #include <linux/ctype.h> > #include <linux/projid.h> > #include <linux/fs_struct.h> > +#include <linux/sched.h> > > static struct kmem_cache *user_ns_cachep __read_mostly; > static DEFINE_MUTEX(userns_state_mutex); > @@ -977,7 +978,7 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns) > return -EINVAL; > > /* Threaded processes may not enter a different user namespace */ > - if (atomic_read(¤t->mm->mm_users) > 1) > + if (!current_is_single_threaded()) > return -EINVAL; > > if (current->fs->users != 1) > -- > 1.9.1
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