tomoyo: fix UAF write bug in tomoyo_write_control()

Since tomoyo_write_control() updates head->write_buf when write()
of long lines is requested, we need to fetch head->write_buf after
head->io_sem is held.  Otherwise, concurrent write() requests can
cause use-after-free-write and double-free problems.

Reported-by: Sam Sun <samsun1006219@gmail.com>
Closes: https://lkml.kernel.org/r/CAEkJfYNDspuGxYx5kym8Lvp--D36CMDUErg4rxfWFJuPbbji8g@mail.gmail.com
Fixes: bd03a3e4c9a9 ("TOMOYO: Add policy namespace support.")
Cc:  <stable@vger.kernel.org> # Linux 3.1+
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/security/tomoyo/common.c b/security/tomoyo/common.c
index 57ee70a..ea3140d 100644 (file)
--- a/security/tomoyo/common.c
+++ b/security/tomoyo/common.c
@@ -2649,13 +2649,14 @@ ssize_t tomoyo_write_control(struct tomoyo_io_buffer *head,
 {
        int error = buffer_len;
        size_t avail_len = buffer_len;
-       char *cp0 = head->write_buf;
+       char *cp0;
        int idx;
 
        if (!head->write)
                return -EINVAL;
        if (mutex_lock_interruptible(&head->io_sem))
                return -EINTR;
+       cp0 = head->write_buf;
        head->read_user_buf_avail = 0;
        idx = tomoyo_read_lock();
        /* Read a line and dispatch it to the policy handler. */