[PATCH 4.19 77/92] nfs: Fix getxattr kernel panic and memory overflow

[Greg Kroah-Hartman]

From: Jeffrey Mitchell <jeffrey.mitch...@starlab.io>

[ Upstream commit b4487b93545214a9db8cbf32e86411677b0cca21 ]

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.mitch...@starlab.io>
[Trond: clean up duplicate test of label->len != 0]
Signed-off-by: Trond Myklebust <trond.mykleb...@hammerspace.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 fs/nfs/nfs4proc.c | 2 --
 fs/nfs/nfs4xdr.c  | 6 +++++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 05cb68ca1ba1a..1ef75b1deffa3 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5603,8 +5603,6 @@ 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 c4cf0192d7bb8..0a5cae8f8aff9 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -4280,7 +4280,11 @@ static int decode_attr_security_label(struct xdr_stream 
*xdr, uint32_t *bitmap,
                        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;
-- 
2.25.1