[3.11.y.z extended stable] Patch "NFSv4: Fix a use-after-free problem in open()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 237eafffcf4f5bf7988aea135b1e746c7a0d4a77 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust at primarydata.com>
Date: Wed, 26 Mar 2014 13:24:37 -0700
Subject: NFSv4: Fix a use-after-free problem in open()

commit e911b8158ee1def8153849b1641b736026b036e0 upstream.

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 at redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust at primarydata.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 fs/nfs/nfs4proc.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 7690917..9317b38 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -976,6 +976,7 @@ 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);
 }

@@ -2126,10 +2127,12 @@ 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)
@@ -2155,11 +2158,10 @@ static int _nfs4_do_open(struct inode *dir,
 		}
 	}

-	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);

@@ -2169,7 +2171,6 @@ 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);
--
1.9.1