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authorNeilBrown <neilb@suse.de>2010-11-16 08:55:19 +0300
committerJ. Bruce Fields <bfields@redhat.com>2010-12-08 04:39:55 +0300
commited2849d3ecfa339435818eeff28f6c3424300cec (patch)
tree2fbef743779156c2c96afecd8311ff8488a90121 /net/sunrpc/svc_xprt.c
parentcf7d7e5a1980d1116ee152d25dac382b112b9c17 (diff)
downloadlinux-ed2849d3ecfa339435818eeff28f6c3424300cec.tar.xz
sunrpc: prevent use-after-free on clearing XPT_BUSY
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 <neilb@suse.de> Cc: stable@kernel.org Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net/sunrpc/svc_xprt.c')
-rw-r--r--net/sunrpc/svc_xprt.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index ea2ff78dcf7b..3f2c5559ca1a 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -212,6 +212,7 @@ int svc_create_xprt(struct svc_serv *serv, const char *xprt_name,
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;
@@ -230,8 +231,9 @@ int svc_create_xprt(struct svc_serv *serv, const char *xprt_name,
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);
@@ -425,8 +427,13 @@ void svc_xprt_received(struct svc_xprt *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);