On 09/16/2013 05:04 AM, Davidlohr Bueso wrote:
Currently, we check shm security only under RCU. Since selinux
can free the security structure, through selinux_sem_free_security(),
we can run into a use-after-free condition. This bug affects both
shmctl and shmat syscalls.
The fix is obvious, make sure we hold the kern_ipc_perm.lock while
performing these security checks.
Actually: either kern_ipc_perm or down_xx(&shm_ids(ns).rwsem) is sufficient.
Reported-by: Manfred Spraul <manf...@colorfullife.com>
Signed-off-by: Davidlohr Bueso <davidl...@hp.com>
---
ipc/shm.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/ipc/shm.c b/ipc/shm.c
index 2821cdf..bc3e897 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -781,18 +781,17 @@ static int shmctl_down(struct ipc_namespace *ns, int
shmid, int cmd,
shp = container_of(ipcp, struct shmid_kernel, shm_perm);
+ ipc_lock_object(&shp->shm_perm);
err = security_shm_shmctl(shp, cmd);
if (err)
- goto out_unlock1;
+ goto out_unlock0;
This change is not necessary: down_write(shm_ids(ns).rwsem) already
synchronizes against another IPC_RMID.
But it doesn't hurt.
@@ -960,11 +962,12 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct
shmid_ds __user *, buf)
}
audit_ipc_obj(&(shp->shm_perm));
+
+ ipc_lock_object(&shp->shm_perm);
err = security_shm_shmctl(shp, cmd);
What about audit_ipc_obj()?
calls __audit_ipc_obj
calls security_ipc_getsecid
calls security_ops->ipc_getsecid, which can be selinux_ipc_getsecid
selinux_ipc_getsecid dereferences ipcp->security
Please: Restart from 3.0.9 (i.e. before the scalability improvement
project was started)
Every function that is moved from "synchronization with ipc_lock()" to
"only rcu_read_lock() held" must be checked.
--
Manfred
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