[PATCH v2 3/4] NFSv4.2: Fix a memory stomp in decode_attr_security_label

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From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

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

diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 9103e022376a..deec76cf5afe 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -4236,12 +4236,10 @@ static int decode_attr_security_label(struct xdr_stream *xdr, uint32_t *bitmap,
 			return -EIO;
 		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;
-- 
2.37.3




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