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authorElena Reshetova2023-08-17 21:13:32 -0700
committerKees Cook2023-08-21 11:29:12 -0700
commit2ddd3cac1fa988323684cee567356e970e6750bd (patch)
treeaa7fd48cda8f587fdc4308c14ae49ab2199289a4 /kernel
parenta4b35d4d05b9f2e84c1dd6301d3dca65719334ef (diff)
nsproxy: Convert nsproxy.count to refcount_t
atomic_t variables are currently used to implement reference counters with the following properties: - counter is initialized to 1 using atomic_set() - a resource is freed upon counter reaching zero - once counter reaches zero, its further increments aren't allowed - counter schema uses basic atomic operations (set, inc, inc_not_zero, dec_and_test, etc.) Such atomic variables should be converted to a newly provided refcount_t type and API that prevents accidental counter overflows and underflows. This is important since overflows and underflows can lead to use-after-free situation and be exploitable. The variable nsproxy.count is used as pure reference counter. Convert it to refcount_t and fix up the operations. **Important note for maintainers: Some functions from refcount_t API defined in refcount.h have different memory ordering guarantees than their atomic counterparts. Please check Documentation/core-api/refcount-vs-atomic.rst for more information. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the nsproxy.count it might make a difference in following places: - put_nsproxy() and switch_task_namespaces(): decrement in refcount_dec_and_test() only provides RELEASE ordering and ACQUIRE ordering on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook <keescook@chromium.org> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> Reviewed-by: David Windsor <dwindsor@gmail.com> Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com> Reviewed-by: Christian Brauner <brauner@kernel.org> Link: https://lore.kernel.org/r/20230818041327.gonna.210-kees@kernel.org Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/nsproxy.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 80d9c6d77a45..15781acaac1c 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -30,7 +30,7 @@
static struct kmem_cache *nsproxy_cachep;
struct nsproxy init_nsproxy = {
- .count = ATOMIC_INIT(1),
+ .count = REFCOUNT_INIT(1),
.uts_ns = &init_uts_ns,
#if defined(CONFIG_POSIX_MQUEUE) || defined(CONFIG_SYSVIPC)
.ipc_ns = &init_ipc_ns,
@@ -55,7 +55,7 @@ static inline struct nsproxy *create_nsproxy(void)
nsproxy = kmem_cache_alloc(nsproxy_cachep, GFP_KERNEL);
if (nsproxy)
- atomic_set(&nsproxy->count, 1);
+ refcount_set(&nsproxy->count, 1);
return nsproxy;
}