[PATCH] selinux: convert struct sidtab count to refcount_t

NitinGote
2019-07-22T11:35:40Z

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: NitinGote <nitin.r.gote@intel.com>
---
security/selinux/ss/sidtab.c | 16 ++++++++--------
security/selinux/ss/sidtab.h | 2 +-
2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/security/selinux/ss/sidtab.c b/security/selinux/ss/sidtab.c
index e63a90ff2728..20fe235c6c71 100644
--- a/security/selinux/ss/sidtab.c
+++ b/security/selinux/ss/sidtab.c
@@ -29,7 +29,7 @@ int sidtab_init(struct sidtab *s)
for (i = 0; i < SECINITSID_NUM; i++)
s->isids[i].set = 0;

- atomic_set(&s->count, 0);
+ refcount_set(&s->count, 0);

s->convert = NULL;

@@ -130,7 +130,7 @@ static struct context *sidtab_do_lookup(struct sidtab *s, u32 index, int alloc)

static struct context *sidtab_lookup(struct sidtab *s, u32 index)
{
- u32 count = (u32)atomic_read(&s->count);
+ u32 count = refcount_read(&s->count);

if (index >= count)
return NULL;
@@ -245,7 +245,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
u32 *index)
{
unsigned long flags;
- u32 count = (u32)atomic_read(&s->count);
+ u32 count = (u32)refcount_read(&s->count);
u32 count_locked, level, pos;
struct sidtab_convert_params *convert;
struct context *dst, *dst_convert;
@@ -272,7 +272,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
spin_lock_irqsave(&s->lock, flags);

convert = s->convert;
- count_locked = (u32)atomic_read(&s->count);
+ count_locked = (u32)refcount_read(&s->count);
level = sidtab_level_from_count(count_locked);

/* if count has changed before we acquired the lock, then catch up */
@@ -315,7 +315,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
}

/* at this point we know the insert won't fail */
- atomic_set(&convert->target->count, count + 1);
+ refcount_set(&convert->target->count, count + 1);
}

if (context->len)
@@ -328,7 +328,7 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
/* write entries before writing new count */
smp_wmb();

- atomic_set(&s->count, count + 1);
+ refcount_set(&s->count, count + 1);

rc = 0;
out_unlock:
@@ -418,7 +418,7 @@ int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params)
return -EBUSY;
}

- count = (u32)atomic_read(&s->count);
+ count = (u32)refcount_read(&s->count);
level = sidtab_level_from_count(count);

/* allocate last leaf in the new sidtab (to avoid race with
@@ -431,7 +431,7 @@ int sidtab_convert(struct sidtab *s, struct sidtab_convert_params *params)
}

/* set count in case no new entries are added during conversion */
- atomic_set(&params->target->count, count);
+ refcount_set(&params->target->count, count);

/* enable live convert of new entries */
s->convert = params;
diff --git a/security/selinux/ss/sidtab.h b/security/selinux/ss/sidtab.h
index bbd5c0d1f3bd..68dd96a5beba 100644
--- a/security/selinux/ss/sidtab.h
+++ b/security/selinux/ss/sidtab.h
@@ -70,7 +70,7 @@ struct sidtab_convert_params {

struct sidtab {
union sidtab_entry_inner roots[SIDTAB_MAX_LEVEL + 1];
- atomic_t count;
+ refcount_t count;
struct sidtab_convert_params *convert;
spinlock_t lock;

--
2.17.1