(apologies for the dup, forgot to reply all) userns_install in user_namespace.c (affects setns of a user namespace): cde1975bc242f3e1072bde623ef378e547b73f91.
The check in check_unshare_flags is a little more complex. The incorrect check was added in cf2e340f4249b781b3d2beb41e891d08581f0e10 but I don't think it would have triggered under any supported combination of flags at that point. >From 50804fe3737ca6a5942fdc2057a18a8141d00141 until 6e556ce209b09528dbf1931cbfd5d323e1345926, the bug affected unshare(CLONE_NEWPID). >From b2e0d98705e60e45bbb3c0032c48824ad7ae0704 onward, unshare(CLONE_NEWUSER) is affected. Thanks, Ricky On Tue, Jul 28, 2015 at 11:17 AM, Eric W. Biederman <ebied...@xmission.com> wrote: > Kees Cook <keesc...@chromium.org> writes: > >> From: Ricky Zhou <ric...@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 <ric...@chromium.org> >> Signed-off-by: Kees Cook <keesc...@chromium.org> >> Cc: sta...@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/