This is a note to let you know that I've just added the patch titled
sunrpc: prevent use-after-free on clearing XPT_BUSY
to the 2.6.32-longterm tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/longterm/longterm-queue-2.6.32.git;a=summary
The filename of the patch is:
sunrpc-prevent-use-after-free-on-clearing-xpt_busy.patch
and it can be found in the queue-2.6.32 subdirectory.
If you, or anyone else, feels it should not be added to the 2.6.32 longterm
tree,
please let <[email protected]> know about it.
>From ed2849d3ecfa339435818eeff28f6c3424300cec Mon Sep 17 00:00:00 2001
From: NeilBrown <[email protected]>
Date: Tue, 16 Nov 2010 16:55:19 +1100
Subject: sunrpc: prevent use-after-free on clearing XPT_BUSY
From: NeilBrown <[email protected]>
commit ed2849d3ecfa339435818eeff28f6c3424300cec upstream.
When an xprt is created, it has a refcount of 1, and XPT_BUSY is set.
The refcount is *not* owned by the thread that created the xprt
(as is clear from the fact that creators never put the reference).
Rather, it is owned by the absence of XPT_DEAD. Once XPT_DEAD is set,
(And XPT_BUSY is clear) that initial reference is dropped and the xprt
can be freed.
So when a creator clears XPT_BUSY it is dropping its only reference and
so must not touch the xprt again.
However svc_recv, after calling ->xpo_accept (and so getting an XPT_BUSY
reference on a new xprt), calls svc_xprt_recieved. This clears
XPT_BUSY and then svc_xprt_enqueue - this last without owning a reference.
This is dangerous and has been seen to leave svc_xprt_enqueue working
with an xprt containing garbage.
So we need to hold an extra counted reference over that call to
svc_xprt_received.
For safety, any time we clear XPT_BUSY and then use the xprt again, we
first get a reference, and the put it again afterwards.
Note that svc_close_all does not need this extra protection as there are
no threads running, and the final free can only be called asynchronously
from such a thread.
Signed-off-by: NeilBrown <[email protected]>
Signed-off-by: J. Bruce Fields <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
net/sunrpc/svc_xprt.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -209,6 +209,7 @@ int svc_create_xprt(struct svc_serv *ser
spin_lock(&svc_xprt_class_lock);
list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
struct svc_xprt *newxprt;
+ unsigned short newport;
if (strcmp(xprt_name, xcl->xcl_name))
continue;
@@ -227,8 +228,9 @@ int svc_create_xprt(struct svc_serv *ser
spin_lock_bh(&serv->sv_lock);
list_add(&newxprt->xpt_list, &serv->sv_permsocks);
spin_unlock_bh(&serv->sv_lock);
+ newport = svc_xprt_local_port(newxprt);
clear_bit(XPT_BUSY, &newxprt->xpt_flags);
- return svc_xprt_local_port(newxprt);
+ return newport;
}
err:
spin_unlock(&svc_xprt_class_lock);
@@ -430,8 +432,13 @@ void svc_xprt_received(struct svc_xprt *
{
BUG_ON(!test_bit(XPT_BUSY, &xprt->xpt_flags));
xprt->xpt_pool = NULL;
+ /* As soon as we clear busy, the xprt could be closed and
+ * 'put', so we need a reference to call svc_xprt_enqueue with:
+ */
+ svc_xprt_get(xprt);
clear_bit(XPT_BUSY, &xprt->xpt_flags);
svc_xprt_enqueue(xprt);
+ svc_xprt_put(xprt);
}
EXPORT_SYMBOL_GPL(svc_xprt_received);
Patches currently in longterm-queue-2.6.32 which might be from [email protected] are
_______________________________________________
stable mailing list
[email protected]
http://linux.kernel.org/mailman/listinfo/stable
