[kernel-hardening] [PATCH] shm: fix a race between shm_exit() and shm_init()

Vasiliy Kulikov
2011-08-02T12:45:30Z

Hi,

Manuel, Richard, Marc - can you test this patch, please?

From: Vasiliy Kulikov <segoon@openwall.com>
Subject: [PATCH] shm: fix a race between shm_exit() and shm_init()

On thread exit shm_exit() is called, it uses shm_ids(ns).rw_mutex.
It is initialized in shm_init(), but it is not called yet at the moment
of kernel threads exit. Some kernel threads are created in
do_pre_smp_initcalls(), and shm_init() is called in do_initcalls().

Static initialization of shm_ids(init_ipc_ns).rw_mutex fixes the race.

It fixes a kernel oops:

Unable to handle kernel NULL pointer dereference at virtual address 00000000
...
[<c0320090>] (__down_write_nested+0x88/0xe0) from [<c015da08>] (exit_shm+0x28/0x48)
[<c015da08>] (exit_shm+0x28/0x48) from [<c002e550>] (do_exit+0x59c/0x750)
[<c002e550>] (do_exit+0x59c/0x750) from [<c003eaac>] (____call_usermodehelper+0x13c/0x154)
[<c003eaac>] (____call_usermodehelper+0x13c/0x154) from [<c000f630>] (kernel_thread_exit+0x0/0x8)
Code: 1afffffa e597c00c e58d0000 e587d00c (e58cd000)

Reported-by: Manuel Lauss <manuel.lauss@googlemail.com>
Reported-by: Richard Weinberger <richard@nod.at>
Reported-by: Marc Zyngier <maz@misterjones.org>
Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
---
ipc/msgutil.c | 6 ++++++
ipc/shm.c | 11 ++++++++++-
ipc/util.c | 30 +++++++++++++++++-------------
ipc/util.h | 1 +
4 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/ipc/msgutil.c b/ipc/msgutil.c
index 8b5ce5d..6da67b6 100644
--- a/ipc/msgutil.c
+++ b/ipc/msgutil.c
@@ -20,6 +20,9 @@

DEFINE_SPINLOCK(mq_lock);

+#define INIT_IPC_SHM_IDS(name) \
+ { .rw_mutex = __RWSEM_INITIALIZER(name.rw_mutex), }
+
/*
* The next 2 defines are here bc this is the only file
* compiled when either CONFIG_SYSVIPC and CONFIG_POSIX_MQUEUE
@@ -27,6 +30,9 @@ DEFINE_SPINLOCK(mq_lock);
*/
struct ipc_namespace init_ipc_ns = {
.count = ATOMIC_INIT(1),
+ .ids = {
+ [IPC_SHM_IDS] = INIT_IPC_SHM_IDS(init_ipc_ns.ids[IPC_SHM_IDS]),
+ },
#ifdef CONFIG_POSIX_MQUEUE
.mq_queues_max = DFLT_QUEUESMAX,
.mq_msg_max = DFLT_MSGMAX,
diff --git a/ipc/shm.c b/ipc/shm.c
index 9fb044f..7d084a0 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -76,7 +76,16 @@ void shm_init_ns(struct ipc_namespace *ns)
ns->shm_ctlmni = SHMMNI;
ns->shm_rmid_forced = 0;
ns->shm_tot = 0;
- ipc_init_ids(&shm_ids(ns));
+
+ /*
+ * For init_ipc_ns shm_ids().rw_mutex is statically initialized
+ * as kernel threads should be able to use it in do_exit() before
+ * shm_init(), which is called on do_initcall()
+ */
+ if (ns == &init_ipc_ns)
+ __ipc_init_ids(&shm_ids(ns));
+ else
+ ipc_init_ids(&shm_ids(ns));
}

/*
diff --git a/ipc/util.c b/ipc/util.c
index 75261a3..673dde5 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -108,31 +108,35 @@ static int __init ipc_init(void)
}
__initcall(ipc_init);

-/**
- * ipc_init_ids - initialise IPC identifiers
- * @ids: Identifier set
- *
- * Set up the sequence range to use for the ipc identifier range (limited
- * below IPCMNI) then initialise the ids idr.
- */
-
-void ipc_init_ids(struct ipc_ids *ids)
+void __ipc_init_ids(struct ipc_ids *ids)
{
- init_rwsem(&ids->rw_mutex);
-
ids->in_use = 0;
ids->seq = 0;
{
int seq_limit = INT_MAX/SEQ_MULTIPLIER;
if (seq_limit > USHRT_MAX)
ids->seq_max = USHRT_MAX;
- else
- ids->seq_max = seq_limit;
+ else
+ ids->seq_max = seq_limit;
}

idr_init(&ids->ipcs_idr);
}

+/**
+ * ipc_init_ids - initialise IPC identifiers
+ * @ids: Identifier set
+ *
+ * Set up the sequence range to use for the ipc identifier range (limited
+ * below IPCMNI) then initialise the ids idr.
+ */
+
+void ipc_init_ids(struct ipc_ids *ids)
+{
+ init_rwsem(&ids->rw_mutex);
+ __ipc_init_ids(ids);
+}
+
#ifdef CONFIG_PROC_FS
static const struct file_operations sysvipc_proc_fops;
/**
diff --git a/ipc/util.h b/ipc/util.h
index 6f5c20b..8bbcd9c 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -80,6 +80,7 @@ struct seq_file;
struct ipc_ids;

void ipc_init_ids(struct ipc_ids *);
+void __ipc_init_ids(struct ipc_ids *ids);
#ifdef CONFIG_PROC_FS
void __init ipc_init_proc_interface(const char *path, const char *header,
int ids, int (*show)(struct seq_file *, void *));
--
1.7.0.4