[PATCH 4.4 65/97] tcm_fileio: Prevent information leak for short reads

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>


[ Upstream commit f11b55d13563e9428c88c873f4f03a6bef11ec0a ]

If we failed to read data from backing file (probably because some one
truncate file under us), we must zerofill cmd's data, otherwise it will
be returned as is. Most likely cmd's data are unitialized pages from
page cache. This result in information leak.

(Change BUG_ON into -EINVAL se_cmd failure - nab)

testcase: https://github.com/dmonakhov/xfstests/commit/e11a1b7b907ca67b1be51a1594025600767366d5
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/target/target_core_file.c |   23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -276,12 +276,11 @@ static int fd_do_rw(struct se_cmd *cmd,
 	else
 		ret = vfs_iter_read(fd, &iter, &pos);
 
-	kfree(bvec);
-
 	if (is_write) {
 		if (ret < 0 || ret != data_length) {
 			pr_err("%s() write returned %d\n", __func__, ret);
-			return (ret < 0 ? ret : -EINVAL);
+			if (ret >= 0)
+				ret = -EINVAL;
 		}
 	} else {
 		/*
@@ -294,17 +293,29 @@ static int fd_do_rw(struct se_cmd *cmd,
 				pr_err("%s() returned %d, expecting %u for "
 						"S_ISBLK\n", __func__, ret,
 						data_length);
-				return (ret < 0 ? ret : -EINVAL);
+				if (ret >= 0)
+					ret = -EINVAL;
 			}
 		} else {
 			if (ret < 0) {
 				pr_err("%s() returned %d for non S_ISBLK\n",
 						__func__, ret);
-				return ret;
+			} else if (ret != data_length) {
+				/*
+				 * Short read case:
+				 * Probably some one truncate file under us.
+				 * We must explicitly zero sg-pages to prevent
+				 * expose uninizialized pages to userspace.
+				 */
+				if (ret < data_length)
+					ret += iov_iter_zero(data_length - ret, &iter);
+				else
+					ret = -EINVAL;
 			}
 		}
 	}
-	return 1;
+	kfree(bvec);
+	return ret;
 }
 
 static sense_reason_t