TOMOYO: Fix incomplete read after seek.

Commit f23571e8 "TOMOYO: Copy directly to userspace buffer." introduced
tomoyo_flush() that flushes data to be read as soon as possible.
tomoyo_select_domain() (which is called by write()) enqueues data which meant
to be read by next read(), but previous read()'s read buffer's size was not
cleared. As a result, since 2.6.36, sequence like

   char *cp = "select global-pid=1\n";
   read(fd, buf1, sizeof(buf1));
   write(fd, cp, strlen(cp));
   read(fd, buf2, sizeof(buf2));

causes enqueued data to be flushed to buf1 rather than buf2.
Fix this bug by clearing read buffer's size upon write() request.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index 96b7233a0df6..d41900de8a69 100644
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -2591,6 +2591,7 @@ ssize_t tomoyo_write_control(struct tomoyo_io_buffer *head,
                 return -EFAULT;
         if (mutex_lock_interruptible(&head->io_sem))
                 return -EINTR;
+        head->read_user_buf_avail = 0;
         idx = tomoyo_read_lock();
         /* Read a line and dispatch it to the policy handler. */
         while (avail_len > 0) {