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Subject[PATCH 01/15] kernel: convert sighand_struct.count from atomic_t to refcount_t
Date
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@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
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
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