[Devel] [PATCH RHEL7 COMMIT] ms/nfs: Fix getxattr kernel panic and memory overflow

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1127.18.2.vz7.163.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.18.2.vz7.163.20
------>
commit d1d2397a805ae7adb0bb8d2f025a958b7bf8402f
Author: Vasily Averin <vvs at virtuozzo.com>
Date:   Fri Sep 11 12:42:34 2020 +0300

    ms/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
    
    Fixes: aa9c2669626c ("NFS: Client implementation of Labeled-NFS")
    Signed-off-by: Jeffrey Mitchell <jeffrey.mitchell at starlab.io>
    [Trond: clean up duplicate test of label->len != 0]
    Signed-off-by: Trond Myklebust <trond.myklebust at hammerspace.com>
    
    (cherry-picked mainline b4487b935452)
    Fixes CVE-2020-25212
    https://jira.sw.ru/browse/PSBM-107824
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 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 b8d39c6..66b1ec8 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -5337,8 +5337,6 @@ 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 fb91d6c..2145f1d 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -4198,7 +4198,11 @@ 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;