linux-kernel - [PATCH 5.13 260/351] nfsd: fix NULL dereference in nfs3svc_encode

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Message-Id: <20210719144953.550712506@linuxfoundation.org>
Date:   Mon, 19 Jul 2021 16:53:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, JianHong Yin <jiyin@...hat.com>,
        Chuck Lever III <chuck.lever@...cle.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.13 260/351] nfsd: fix NULL dereference in nfs3svc_encode_getaclres

From: J. Bruce Fields <bfields@...hat.com>

[ Upstream commit ab1016d39cc052064e32f25ad18ef8767a0ee3b8 ]

In error cases the dentry may be NULL.

Before 20798dfe249a, the encoder also checked dentry and
d_really_is_positive(dentry), but that looks like overkill to me--zero
status should be enough to guarantee a positive dentry.

This isn't the first time we've seen an error-case NULL dereference
hidden in the initialization of a local variable in an xdr encoder.  But
I went back through the other recent rewrites and didn't spot any
similar bugs.

Reported-by: JianHong Yin <jiyin@...hat.com>
Reviewed-by: Chuck Lever III <chuck.lever@...cle.com>
Fixes: 20798dfe249a ("NFSD: Update the NFSv3 GETACL result encoder...")
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfsd/nfs3acl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs3acl.c b/fs/nfsd/nfs3acl.c
index a1591feeea22..5dfe7644a517 100644
--- a/fs/nfsd/nfs3acl.c
+++ b/fs/nfsd/nfs3acl.c
@@ -172,7 +172,7 @@ static int nfs3svc_encode_getaclres(struct svc_rqst *rqstp, __be32 *p)
 	struct nfsd3_getaclres *resp = rqstp->rq_resp;
 	struct dentry *dentry = resp->fh.fh_dentry;
 	struct kvec *head = rqstp->rq_res.head;
-	struct inode *inode = d_inode(dentry);
+	struct inode *inode;
 	unsigned int base;
 	int n;
 	int w;
@@ -181,6 +181,7 @@ static int nfs3svc_encode_getaclres(struct svc_rqst *rqstp, __be32 *p)
 		return 0;
 	switch (resp->status) {
 	case nfs_ok:
+		inode = d_inode(dentry);
 		if (!svcxdr_encode_post_op_attr(rqstp, xdr, &resp->fh))
 			return 0;
 		if (xdr_stream_encode_u32(xdr, resp->mask) < 0)
-- 
2.30.2