NFSv4: Fix a use-after-free problem in open()

If we interrupt the nfs4_wait_for_completion_rpc_task() call in
nfs4_run_open_task(), then we don't prevent the RPC call from
completing. So freeing up the opendata->f_attr.mdsthreshold
in the error path in _nfs4_do_open() leads to a use-after-free
when the XDR decoder tries to decode the mdsthreshold information
from the server.

Fixes: 82be417aa37c0 (NFSv4.1 cache mdsthreshold values on OPEN)
Tested-by: Steve Dickson <SteveD@redhat.com>
Cc: stable@vger.kernel.org # 3.5+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index c866e325577f..397be39c6dc8 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -1068,6 +1068,7 @@ static void nfs4_opendata_free(struct kref *kref)
         dput(p->dentry);
         nfs_sb_deactive(sb);
         nfs_fattr_free_names(&p->f_attr);
+        kfree(p->f_attr.mdsthreshold);
         kfree(p);
 }
 
@@ -2304,10 +2305,12 @@ static int _nfs4_do_open(struct inode *dir,
                 }
         }
 
-        if (ctx_th && server->attr_bitmask[2] & FATTR4_WORD2_MDSTHRESHOLD) {
-                opendata->f_attr.mdsthreshold = pnfs_mdsthreshold_alloc();
-                if (!opendata->f_attr.mdsthreshold)
-                        goto err_free_label;
+        if (server->attr_bitmask[2] & FATTR4_WORD2_MDSTHRESHOLD) {
+                if (!opendata->f_attr.mdsthreshold) {
+                        opendata->f_attr.mdsthreshold = pnfs_mdsthreshold_alloc();
+                        if (!opendata->f_attr.mdsthreshold)
+                                goto err_free_label;
+                }
                 opendata->o_arg.open_bitmap = &nfs4_pnfs_open_bitmap[0];
         }
         if (dentry->d_inode != NULL)
@@ -2335,11 +2338,10 @@ static int _nfs4_do_open(struct inode *dir,
         if (opendata->file_created)
                 *opened |= FILE_CREATED;
 
-        if (pnfs_use_threshold(ctx_th, opendata->f_attr.mdsthreshold, server))
+        if (pnfs_use_threshold(ctx_th, opendata->f_attr.mdsthreshold, server)) {
                 *ctx_th = opendata->f_attr.mdsthreshold;
-        else
-                kfree(opendata->f_attr.mdsthreshold);
-        opendata->f_attr.mdsthreshold = NULL;
+                opendata->f_attr.mdsthreshold = NULL;
+        }
 
         nfs4_label_free(olabel);
 
@@ -2349,7 +2351,6 @@ static int _nfs4_do_open(struct inode *dir,
 err_free_label:
         nfs4_label_free(olabel);
 err_opendata_put:
-        kfree(opendata->f_attr.mdsthreshold);
         nfs4_opendata_put(opendata);
 err_put_state_owner:
         nfs4_put_state_owner(sp);