[PATCH AUTOSEL for 4.9 156/281] ovl: filter trusted xattr for non-admin

[Sasha Levin]

From: Miklos Szeredi <mszeredi@xxxxxxxxxx>

[ Upstream commit a082c6f680da298cf075886ff032f32ccb7c5e1a ]

Filesystems filter out extended attributes in the "trusted." domain for
unprivlieged callers.

Overlay calls underlying filesystem's method with elevated privs, so need
to do the filtering in overlayfs too.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 fs/overlayfs/inode.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 7fb53d055537..16f6db88c8e5 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -227,6 +227,16 @@ int ovl_xattr_get(struct dentry *dentry, const char *name,
 	return res;
 }
 
+static bool ovl_can_list(const char *s)
+{
+	/* List all non-trusted xatts */
+	if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
+		return true;
+
+	/* Never list trusted.overlay, list other trusted for superuser only */
+	return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
+}
+
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 {
 	struct dentry *realdentry = ovl_dentry_real(dentry);
@@ -250,7 +260,7 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 			return -EIO;
 
 		len -= slen;
-		if (ovl_is_private_xattr(s)) {
+		if (!ovl_can_list(s)) {
 			res -= slen;
 			memmove(s, s + slen, len);
 		} else {
-- 
2.14.1