Various forms of ipc use the ipcctl_pre_down() function to
retrieve an ipc object and check permissions, mostly for IPC_RMID
and IPC_SET commands.
Introduce ipcctl_pre_down_nolock(), a lockless version of this function.
The locking version is maintained, yet modified to call the nolock version,
without affecting its semantics, thus transparent to all ipc callers.
Signed-off-by: Davidlohr Bueso <davidlohr.bu...@hp.com>
Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
---
ipc/util.c | 31 ++++++++++++++++++++++++++-----
ipc/util.h | 3 +++
2 files changed, 29 insertions(+), 5 deletions(-)
diff --git a/ipc/util.c b/ipc/util.c
index 65c3d6c..6a98e62 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -825,11 +825,28 @@ struct kern_ipc_perm *ipcctl_pre_down(struct
ipc_namespace *ns,
struct ipc64_perm *perm, int extra_perm)
{
struct kern_ipc_perm *ipcp;
+
+ ipcp = ipcctl_pre_down_nolock(ns, ids, id, cmd, perm, extra_perm);
+ if (IS_ERR(ipcp))
+ goto out;
+
+ spin_lock(&ipcp->lock);
+out:
+ return ipcp;
+}
+
+struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
+ struct ipc_ids *ids, int id, int
cmd,
+ struct ipc64_perm *perm, int
extra_perm)
+{
kuid_t euid;
- int err;
+ int err = -EPERM;
+ struct kern_ipc_perm *ipcp;
down_write(&ids->rw_mutex);
- ipcp = ipc_lock_check(ids, id);
+ rcu_read_lock();
+
+ ipcp = ipc_obtain_object_check(ids, id);
if (IS_ERR(ipcp)) {
err = PTR_ERR(ipcp);
goto out_up;
@@ -838,17 +855,21 @@ struct kern_ipc_perm *ipcctl_pre_down(struct
ipc_namespace *ns,
audit_ipc_obj(ipcp);
if (cmd == IPC_SET)
audit_ipc_set_perm(extra_perm, perm->uid,
- perm->gid, perm->mode);
+ perm->gid, perm->mode);
euid = current_euid();
if (uid_eq(euid, ipcp->cuid) || uid_eq(euid, ipcp->uid) ||
ns_capable(ns->user_ns, CAP_SYS_ADMIN))
return ipcp;
- err = -EPERM;
- ipc_unlock(ipcp);
out_up:
+ /*
+ * Unsuccessful lookup, unlock and return
+ * the corresponding error.
+ */
+ rcu_read_unlock();
up_write(&ids->rw_mutex);
+
return ERR_PTR(err);
}
diff --git a/ipc/util.h b/ipc/util.h
index bfc8d4e..13d92fe 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -128,6 +128,9 @@ struct kern_ipc_perm *ipc_obtain_object(struct ipc_ids
*ids, int id);
void kernel_to_ipc64_perm(struct kern_ipc_perm *in, struct ipc64_perm *out);
void ipc64_perm_to_ipc_perm(struct ipc64_perm *in, struct ipc_perm *out);
int ipc_update_perm(struct ipc64_perm *in, struct kern_ipc_perm *out);
+struct kern_ipc_perm *ipcctl_pre_down_nolock(struct ipc_namespace *ns,
+ struct ipc_ids *ids, int id, int
cmd,
+ struct ipc64_perm *perm, int
extra_perm);
struct kern_ipc_perm *ipcctl_pre_down(struct ipc_namespace *ns,
struct ipc_ids *ids, int id, int cmd,
struct ipc64_perm *perm, int extra_perm);
--
1.7.11.7
--
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