Commit d9226ec9 authored by Elena Reshetova's avatar Elena Reshetova Committed by J. Bruce Fields

lockd: convert nlm_rqst.a_count from atomic_t 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 nlm_rqst.a_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 lib/refcount.c
have different memory ordering guarantees than their atomic
counterparts.
The full comparison can be seen in
https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
in state to be merged to the documentation tree.
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 nlm_rqst.a_count it might make a difference
in following places:
 - nlmclnt_release_call() and nlmsvc_release_call(): decrement
   in refcount_dec_and_test() only
   provides RELEASE ordering and control dependency on success
   vs. fully ordered atomic counterpart
Suggested-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarDavid Windsor <dwindsor@gmail.com>
Reviewed-by: default avatarHans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: default avatarElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent 8bb3ea77
...@@ -204,7 +204,7 @@ struct nlm_rqst *nlm_alloc_call(struct nlm_host *host) ...@@ -204,7 +204,7 @@ struct nlm_rqst *nlm_alloc_call(struct nlm_host *host)
for(;;) { for(;;) {
call = kzalloc(sizeof(*call), GFP_KERNEL); call = kzalloc(sizeof(*call), GFP_KERNEL);
if (call != NULL) { if (call != NULL) {
atomic_set(&call->a_count, 1); refcount_set(&call->a_count, 1);
locks_init_lock(&call->a_args.lock.fl); locks_init_lock(&call->a_args.lock.fl);
locks_init_lock(&call->a_res.lock.fl); locks_init_lock(&call->a_res.lock.fl);
call->a_host = nlm_get_host(host); call->a_host = nlm_get_host(host);
...@@ -222,7 +222,7 @@ void nlmclnt_release_call(struct nlm_rqst *call) ...@@ -222,7 +222,7 @@ void nlmclnt_release_call(struct nlm_rqst *call)
{ {
const struct nlmclnt_operations *nlmclnt_ops = call->a_host->h_nlmclnt_ops; const struct nlmclnt_operations *nlmclnt_ops = call->a_host->h_nlmclnt_ops;
if (!atomic_dec_and_test(&call->a_count)) if (!refcount_dec_and_test(&call->a_count))
return; return;
if (nlmclnt_ops && nlmclnt_ops->nlmclnt_release_call) if (nlmclnt_ops && nlmclnt_ops->nlmclnt_release_call)
nlmclnt_ops->nlmclnt_release_call(call->a_callback_data); nlmclnt_ops->nlmclnt_release_call(call->a_callback_data);
...@@ -678,7 +678,7 @@ nlmclnt_unlock(struct nlm_rqst *req, struct file_lock *fl) ...@@ -678,7 +678,7 @@ nlmclnt_unlock(struct nlm_rqst *req, struct file_lock *fl)
goto out; goto out;
} }
atomic_inc(&req->a_count); refcount_inc(&req->a_count);
status = nlmclnt_async_call(nfs_file_cred(fl->fl_file), req, status = nlmclnt_async_call(nfs_file_cred(fl->fl_file), req,
NLMPROC_UNLOCK, &nlmclnt_unlock_ops); NLMPROC_UNLOCK, &nlmclnt_unlock_ops);
if (status < 0) if (status < 0)
...@@ -769,7 +769,7 @@ static int nlmclnt_cancel(struct nlm_host *host, int block, struct file_lock *fl ...@@ -769,7 +769,7 @@ static int nlmclnt_cancel(struct nlm_host *host, int block, struct file_lock *fl
nlmclnt_setlockargs(req, fl); nlmclnt_setlockargs(req, fl);
req->a_args.block = block; req->a_args.block = block;
atomic_inc(&req->a_count); refcount_inc(&req->a_count);
status = nlmclnt_async_call(nfs_file_cred(fl->fl_file), req, status = nlmclnt_async_call(nfs_file_cred(fl->fl_file), req,
NLMPROC_CANCEL, &nlmclnt_cancel_ops); NLMPROC_CANCEL, &nlmclnt_cancel_ops);
if (status == 0 && req->a_res.status == nlm_lck_denied) if (status == 0 && req->a_res.status == nlm_lck_denied)
......
...@@ -295,7 +295,7 @@ static void nlmsvc_callback_exit(struct rpc_task *task, void *data) ...@@ -295,7 +295,7 @@ static void nlmsvc_callback_exit(struct rpc_task *task, void *data)
void nlmsvc_release_call(struct nlm_rqst *call) void nlmsvc_release_call(struct nlm_rqst *call)
{ {
if (!atomic_dec_and_test(&call->a_count)) if (!refcount_dec_and_test(&call->a_count))
return; return;
nlmsvc_release_host(call->a_host); nlmsvc_release_host(call->a_host);
kfree(call); kfree(call);
......
...@@ -136,7 +136,7 @@ struct nlm_wait; ...@@ -136,7 +136,7 @@ struct nlm_wait;
*/ */
#define NLMCLNT_OHSIZE ((__NEW_UTS_LEN) + 10u) #define NLMCLNT_OHSIZE ((__NEW_UTS_LEN) + 10u)
struct nlm_rqst { struct nlm_rqst {
atomic_t a_count; refcount_t a_count;
unsigned int a_flags; /* initial RPC task flags */ unsigned int a_flags; /* initial RPC task flags */
struct nlm_host * a_host; /* host handle */ struct nlm_host * a_host; /* host handle */
struct nlm_args a_args; /* arguments */ struct nlm_args a_args; /* arguments */
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment