From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Tue, 18 Oct 2022 18:21:14 -0400
Subject: [PATCH] NFSv4.2: Fix a memory stomp in decode_attr_security_label
Git-commit: 43c1031f7110967c240cb6e922adcfc4b8899183
Patch-mainline: v6.2
References: git-fixes

We must not change the value of label->len if it is zero, since that
indicates we stored a label.

Fixes: b4487b935452 ("nfs: Fix getxattr kernel panic and memory overflow")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/nfs4xdr.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -4167,12 +4167,10 @@ static int decode_attr_security_label(st
 			goto out_overflow;
 		bitmap[2] &= ~FATTR4_WORD2_SECURITY_LABEL;
 		if (len < NFS4_MAXLABELLEN) {
-			if (label) {
-				if (label->len) {
-					if (label->len < len)
-						return -ERANGE;
-					memcpy(label->label, p, len);
-				}
+			if (label && label->len) {
+				if (label->len < len)
+					return -ERANGE;
+				memcpy(label->label, p, len);
 				label->len = len;
 				label->pi = pi;
 				label->lfs = lfs;