[PATCH] LSM: add missing hook to do_compat_readv_writev()

This patch addresses a flaw in LSM, where there is no mediation of readv()
and writev() in for 32-bit compatible apps using a 64-bit kernel.

This bug was discovered and fixed initially in the native readv/writev
code [1], but was not fixed in the compat code. Thanks to Al for spotting
this one.

[1] http://lwn.net/Articles/154282/

Signed-off-by: James Morris <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/compat.c

···
 	if (ret < 0)
 		goto out;
 
+	ret = security_file_permission(file, type == READ ? MAY_READ:MAY_WRITE);
+	if (ret)
+		goto out;
+
 	fnv = NULL;
 	if (type == READ) {
 		fn = file->f_op->read;