[PATCH 01/19] 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. Signed-off-by: Elena Reshetova <elena.reshetova(a)intel.com&gt; Signed-off-by: Hans Liljestrand <ishkamiel(a)gmail.com&gt; Signed-off-by: Kees Cook <keescook(a)chromium.org&gt; Signed-off-by: David Windsor <dwindsor(a)gmail.com&gt; --- fs/exec.c | 4 ++-- include/linux/init_task.h | 2 +- include/linux/sched.h | 3 ++- kernel/fork.c | 8 ++++---- 4 files changed, 9 insertions(+), 8 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 698a860..3f78ff2 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1174,7 +1174,7 @@ 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 @@ -1184,7 +1184,7 @@ 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/include/linux/init_task.h b/include/linux/init_task.h index 3a85d61..1f160b2 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -82,7 +82,7 @@ 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.h b/include/linux/sched.h index 0f0d497..a0430aa 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -42,6 +42,7 @@ struct sched_param { #include <linux/seccomp.h> #include <linux/rcupdate.h> #include <linux/rculist.h> +#include <linux/refcount.h> #include <linux/rtmutex.h> #include <linux/time.h> @@ -527,7 +528,7 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK) 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 e96e256..9488f01 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1285,7 +1285,7 @@ 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); @@ -1293,14 +1293,14 @@ 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_DESTROY_BY_RCU so we can free it @@ -2170,7 +2170,7 @@ 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