[PATCH 11/15] kernel: convert group_info.usage 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; --- include/linux/cred.h | 7 ++++--- kernel/cred.c | 2 +- kernel/groups.c | 2 +- 3 files changed, 6 insertions(+), 5 deletions(-) diff --git a/include/linux/cred.h b/include/linux/cred.h index 099058e..00948dd 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -17,6 +17,7 @@ #include <linux/key.h> #include <linux/selinux.h> #include <linux/atomic.h> +#include <linux/refcount.h> #include <linux/uidgid.h> #include <linux/sched.h> #include <linux/sched/user.h> @@ -28,7 +29,7 @@ struct inode; * COW Supplementary groups list */ struct group_info { - atomic_t usage; + refcount_t usage; int ngroups; kgid_t gid[0]; } __randomize_layout; @@ -44,7 +45,7 @@ struct group_info { */ static inline struct group_info *get_group_info(struct group_info *gi) { - atomic_inc(&gi->usage); + refcount_inc(&gi->usage); return gi; } @@ -54,7 +55,7 @@ static inline struct group_info *get_group_info(struct group_info *gi) */ #define put_group_info(group_info) \ do { \ - if (atomic_dec_and_test(&(group_info)->usage)) \ + if (refcount_dec_and_test(&(group_info)->usage)) \ groups_free(group_info); \ } while (0) diff --git a/kernel/cred.c b/kernel/cred.c index ecf0365..8122d7c 100644 --- a/kernel/cred.c +++ b/kernel/cred.c @@ -36,7 +36,7 @@ do { \ static struct kmem_cache *cred_jar; /* init to 2 - one for init_task, one to ensure it is never freed */ -struct group_info init_groups = { .usage = ATOMIC_INIT(2) }; +struct group_info init_groups = { .usage = REFCOUNT_INIT(2) }; /* * The initial credentials for the initial task diff --git a/kernel/groups.c b/kernel/groups.c index 434f666..5fc6e21 100644 --- a/kernel/groups.c +++ b/kernel/groups.c @@ -23,7 +23,7 @@ struct group_info *groups_alloc(int gidsetsize) if (!gi) return NULL; - atomic_set(&gi->usage, 1); + refcount_set(&gi->usage, 1); gi->ngroups = gidsetsize; return gi; } -- 2.7.4