Messages in this thread | | | From | (Eric W. Biederman) | Date | Wed, 11 Sep 2019 12:32:17 -0500 | Subject | Re: [PATCH v2] fork: check exit_signal passed in clone3() call |
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Eugene Syromiatnikov <esyr@redhat.com> writes:
> Previously, higher 32 bits of exit_signal fields were lost when > copied to the kernel args structure (that uses int as a type for the > respective field). Moreover, as Oleg has noted[1], exit_signal is used > unchecked, so it has to be checked for sanity before use; for the legacy > syscalls, applying CSIGNAL mask guarantees that it is at least non-negative; > however, there's no such thing is done in clone3() code path, and that can > break at least thread_group_leader. > > Checking user-passed exit_signal against ~CSIGNAL mask solves both > of these problems. > > [1] https://lkml.org/lkml/2019/9/10/467 > > * kernel/fork.c (copy_clone_args_from_user): Fail with -EINVAL if > args.exit_signal has bits set outside CSIGNAL mask. > (_do_fork): Note that exit_signal is expected to be checked for the > sanity by the caller. > > Fixes: 7f192e3cd316 ("fork: add clone3") > Reported-by: Oleg Nesterov <oleg@redhat.com> > Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
> --- > kernel/fork.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 2852d0e..9dee2ab 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -2338,6 +2338,8 @@ struct mm_struct *copy_init_mm(void) > * > * It copies the process, and if successful kick-starts > * it and waits for it to finish using the VM if required. > + * > + * args->exit_signal is expected to be checked for sanity by the caller. > */ > long _do_fork(struct kernel_clone_args *args) > { > @@ -2562,6 +2564,16 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs, > if (copy_from_user(&args, uargs, size)) > return -EFAULT; > > + /* > + * exit_signal is confined to CSIGNAL mask in legacy syscalls, > + * so it is used unchecked deeper in syscall handling routines; > + * moreover, copying to struct kernel_clone_args.exit_signals > + * trims higher 32 bits, so it is has to be checked that they > + * are zero. > + */ > + if (unlikely(args.exit_signal & ~((u64)CSIGNAL))) > + return -EINVAL; > + > *kargs = (struct kernel_clone_args){ > .flags = args.flags, > .pidfd = u64_to_user_ptr(args.pidfd),
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