[ 029/180] tty_audit: fix tty_audit_add_data live lock on audit disabled

[Willy Tarreau]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

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

From: Xiaotian Feng <dfeng@xxxxxxxxxx>

commit 00bff392c81e4fb1901e5160fdd5afdb2546a6ab upstream.

The current tty_audit_add_data code:

        do {
                size_t run;

                run = N_TTY_BUF_SIZE - buf->valid;
                if (run > size)
                        run = size;
                memcpy(buf->data + buf->valid, data, run);
                buf->valid += run;
                data += run;
                size -= run;
                if (buf->valid == N_TTY_BUF_SIZE)
                        tty_audit_buf_push_current(buf);
        } while (size != 0);

If the current buffer is full, kernel will then call tty_audit_buf_push_current
to empty the buffer. But if we disabled audit at the same time, tty_audit_buf_push()
returns immediately if audit_enabled is zero.  Without emptying the buffer.
With obvious effect on tty_audit_add_data() that ends up spinning in that loop,
copying 0 bytes at each iteration and attempting to push each time without any effect.
Holding the lock all along.

Suggested-by: Alexander Viro <aviro@xxxxxxxxxx>
Signed-off-by: Xiaotian Feng <dfeng@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 drivers/char/tty_audit.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/char/tty_audit.c b/drivers/char/tty_audit.c
index ac16fbe..dd4691a 100644
--- a/drivers/char/tty_audit.c
+++ b/drivers/char/tty_audit.c
@@ -94,8 +94,10 @@ static void tty_audit_buf_push(struct task_struct *tsk, uid_t loginuid,
 {
 	if (buf->valid == 0)
 		return;
-	if (audit_enabled == 0)
+	if (audit_enabled == 0) {
+		buf->valid = 0;
 		return;
+	}
 	tty_audit_log("tty", tsk, loginuid, sessionid, buf->major, buf->minor,
 		      buf->data, buf->valid);
 	buf->valid = 0;
-- 
1.7.2.1.45.g54fbc



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