From: Jeffrey Mitchell <jeffrey.mitchell@starlab.io>
Date: Wed, 5 Aug 2020 12:23:19 -0500
Subject: [PATCH] nfs: Fix getxattr kernel panic and memory overflow
Git-commit: b4487b93545214a9db8cbf32e86411677b0cca21
Patch-mainline: v5.9
References: bsc#1176381 CVE-2020-25212

Move the buffer size check to decode_attr_security_label() before memcpy()
Only call memcpy() if the buffer is large enough

Fixes: aa9c2669626c ("NFS: Client implementation of Labeled-NFS")
Signed-off-by: Jeffrey Mitchell <jeffrey.mitchell@starlab.io>
[trond: clean up duplicate test of label->len != 0]
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/nfs4proc.c |    2 --
 fs/nfs/nfs4xdr.c  |    6 +++++-
 2 files changed, 5 insertions(+), 3 deletions(-)

--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5337,8 +5337,6 @@ static int _nfs4_get_security_label(stru
 		return ret;
 	if (!(fattr.valid & NFS_ATTR_FATTR_V4_SECURITY_LABEL))
 		return -ENOENT;
-	if (buflen < label.len)
-		return -ERANGE;
 	return 0;
 }
 
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -4166,7 +4166,11 @@ static int decode_attr_security_label(st
 			goto out_overflow;
 		if (len < NFS4_MAXLABELLEN) {
 			if (label) {
-				memcpy(label->label, p, len);
+				if (label->len) {
+					if (label->len < len)
+						return -ERANGE;
+					memcpy(label->label, p, len);
+				}
 				label->len = len;
 				label->pi = pi;
 				label->lfs = lfs;