linux-kernel - [PATCH] nfs: Fix getxattr kernel panic and memory overflow

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Message-Id: <20200805172319.12633-2-jeffrey.mitchell@starlab.io>
Date:   Wed,  5 Aug 2020 12:23:19 -0500
From:   Jeffrey Mitchell <jeffrey.mitchell@...rlab.io>
To:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>
Cc:     linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jeffrey Mitchell <jeffrey.mitchell@...rlab.io>
Subject: [PATCH] nfs: Fix getxattr kernel panic and memory overflow

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

Signed-off-by: Jeffrey Mitchell <jeffrey.mitchell@...rlab.io>
---
 fs/nfs/nfs4proc.c | 2 --
 fs/nfs/nfs4xdr.c  | 5 ++++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 2e2dac29a9e9..45e0585e0667 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5845,8 +5845,6 @@ static int _nfs4_get_security_label(struct inode *inode, void *buf,
 		return ret;
 	if (!(fattr.valid & NFS_ATTR_FATTR_V4_SECURITY_LABEL))
 		return -ENOENT;
-	if (buflen < label.len)
-		return -ERANGE;
 	return 0;
 }
 
diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 47817ef0aadb..50162e0a959c 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -4166,7 +4166,10 @@ static int decode_attr_security_label(struct xdr_stream *xdr, uint32_t *bitmap,
 			return -EIO;
 		if (len < NFS4_MAXLABELLEN) {
 			if (label) {
-				memcpy(label->label, p, len);
+				if (label->len && label->len < len)
+					return -ERANGE;
+				if (label->len)
+					memcpy(label->label, p, len);
 				label->len = len;
 				label->pi = pi;
 				label->lfs = lfs;
-- 
2.25.1