[PATCH 01/15] kernel: convert sighand_struct.count from atomic_t to refcount_t

refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This allows to avoid accidental refcounter overflows that might lead to use-after-free situations. Suggested-by: Kees Cook <keescook(a)chromium.org&gt; Reviewed-by: David Windsor <dwindsor(a)gmail.com&gt; Reviewed-by: Hans Liljestrand <ishkamiel(a)gmail.com&gt; Signed-off-by: Elena Reshetova <elena.reshetova(a)intel.com&gt; --- fs/exec.c | 4 ++-- fs/proc/task_nommu.c | 2 +- include/linux/init_task.h | 2 +- include/linux/sched/signal.h | 3 ++- kernel/fork.c | 8 ++++---- 5 files changed, 10 insertions(+), 9 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 62175cb..75e2800 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1200,7 +1200,7 @@ static int de_thread(struct task_struct *tsk) flush_itimer_signals(); #endif - if (atomic_read(&oldsighand->count) != 1) { + if (refcount_read(&oldsighand->count) != 1) { struct sighand_struct *newsighand; /* * This ->sighand is shared with the CLONE_SIGHAND @@ -1210,7 +1210,7 @@ static int de_thread(struct task_struct *tsk) if (!newsighand) return -ENOMEM; - atomic_set(&newsighand->count, 1); + refcount_set(&newsighand->count, 1); memcpy(newsighand->action, oldsighand->action, sizeof(newsighand->action)); diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c index 38ca416..eea6b91 100644 --- a/fs/proc/task_nommu.c +++ b/fs/proc/task_nommu.c @@ -63,7 +63,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) else bytes += kobjsize(current->files); - if (current->sighand && atomic_read(&current->sighand->count) > 1) + if (current->sighand && refcount_read(&current->sighand->count) > 1) sbytes += kobjsize(current->sighand); else bytes += kobjsize(current->sighand); diff --git a/include/linux/init_task.h b/include/linux/init_task.h index a2f6707..61777d6 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -85,7 +85,7 @@ extern struct fs_struct init_fs; extern struct nsproxy init_nsproxy; #define INIT_SIGHAND(sighand) { \ - .count = ATOMIC_INIT(1), \ + .count = REFCOUNT_INIT(1), \ .action = { { { .sa_handler = SIG_DFL, } }, }, \ .siglock = __SPIN_LOCK_UNLOCKED(sighand.siglock), \ .signalfd_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(sighand.signalfd_wqh), \ diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 2a0dd40..4d5cdf1 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -7,13 +7,14 @@ #include <linux/sched/jobctl.h> #include <linux/sched/task.h> #include <linux/cred.h> +#include <linux/refcount.h> /* * Types defining task->signal and task->sighand and APIs using them: */ struct sighand_struct { - atomic_t count; + refcount_t count; struct k_sigaction action[_NSIG]; spinlock_t siglock; wait_queue_head_t signalfd_wqh; diff --git a/kernel/fork.c b/kernel/fork.c index 080688f..60bd7bf 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1317,7 +1317,7 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) struct sighand_struct *sig; if (clone_flags & CLONE_SIGHAND) { - atomic_inc(&current->sighand->count); + refcount_inc(&current->sighand->count); return 0; } sig = kmem_cache_alloc(sighand_cachep, GFP_KERNEL); @@ -1325,14 +1325,14 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) if (!sig) return -ENOMEM; - atomic_set(&sig->count, 1); + refcount_set(&sig->count, 1); memcpy(sig->action, current->sighand->action, sizeof(sig->action)); return 0; } void __cleanup_sighand(struct sighand_struct *sighand) { - if (atomic_dec_and_test(&sighand->count)) { + if (refcount_dec_and_test(&sighand->count)) { signalfd_cleanup(sighand); /* * sighand_cachep is SLAB_TYPESAFE_BY_RCU so we can free it @@ -2236,7 +2236,7 @@ static int check_unshare_flags(unsigned long unshare_flags) return -EINVAL; } if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) { - if (atomic_read(&current->sighand->count) > 1) + if (refcount_read(&current->sighand->count) > 1) return -EINVAL; } if (unshare_flags & CLONE_VM) { -- 2.7.4