[PATCH 5.13 260/351] nfsd: fix NULL dereference in nfs3svc_encode_getaclres

From: Greg Kroah-Hartman
Date: Mon Jul 19 2021 - 13:43:43 EST

From: J. Bruce Fields <bfields@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Reviewed-by: Chuck Lever III <chuck.lever@xxxxxxxxxx>
Fixes: 20798dfe249a ("NFSD: Update the NFSv3 GETACL result encoder...")
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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)