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tty: audit: Remove tty_audit_buf reference counting 

When tty_audit_exit() is called from do_exit(), the process is
single-threaded. Since the tty_audit_buf is only shared by threads
of a process, no other thread can be concurrently accessing the
tty_audit_buf during or after tty_audit_exit().

Thus, no other thread can be holding an extra tty_audit_buf reference
which would prevent tty_audit_exit() from freeing the tty_audit_buf.
As that is the only purpose of the ref counting, remove the reference
counting and free the tty_audit_buf directly.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2016-01-09 22:55:35 -08:00 committed by Greg Kroah-Hartman
parent 5c8b3185c4
commit 5493090fc2
1 changed files with 7 additions and 40 deletions
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47
drivers/tty/tty_audit.c
View File

@ -14,7 +14,6 @@
#include <linux/tty.h> #include <linux/tty.h>
struct tty_audit_buf { struct tty_audit_buf {
atomic_t count;
struct mutex mutex; /* Protects all data below */ struct mutex mutex; /* Protects all data below */
dev_t dev; /* The TTY which the data is from */ dev_t dev; /* The TTY which the data is from */
unsigned icanon:1; unsigned icanon:1;
@ -32,7 +31,6 @@ static struct tty_audit_buf *tty_audit_buf_alloc(void)
buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL); buf->data = kmalloc(N_TTY_BUF_SIZE, GFP_KERNEL);
if (!buf->data) if (!buf->data)
goto err_buf; goto err_buf;
atomic_set(&buf->count, 1);
mutex_init(&buf->mutex); mutex_init(&buf->mutex);
buf->dev = MKDEV(0, 0); buf->dev = MKDEV(0, 0);
buf->icanon = 0; buf->icanon = 0;
@ -52,12 +50,6 @@ static void tty_audit_buf_free(struct tty_audit_buf *buf)
kfree(buf); kfree(buf);
} }
static void tty_audit_buf_put(struct tty_audit_buf *buf)
{
if (atomic_dec_and_test(&buf->count))
tty_audit_buf_free(buf);
}
static void tty_audit_log(const char *description, dev_t dev, static void tty_audit_log(const char *description, dev_t dev,
unsigned char *data, size_t size) unsigned char *data, size_t size)
{ {
@ -106,6 +98,9 @@ static void tty_audit_buf_push(struct tty_audit_buf *buf)
* *
* Make sure all buffered data is written out and deallocate the buffer. * Make sure all buffered data is written out and deallocate the buffer.
* Only needs to be called if current->signal->tty_audit_buf != %NULL. * Only needs to be called if current->signal->tty_audit_buf != %NULL.
*
* The process is single-threaded at this point; no other threads share
* current->signal.
*/ */
void tty_audit_exit(void) void tty_audit_exit(void)
{ {
@ -116,11 +111,8 @@ void tty_audit_exit(void)
if (!buf) if (!buf)
return; return;
mutex_lock(&buf->mutex);
tty_audit_buf_push(buf); tty_audit_buf_push(buf);
mutex_unlock(&buf->mutex); tty_audit_buf_free(buf);
tty_audit_buf_put(buf);
} }
/** /**
@ -140,21 +132,14 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch)
{ {
struct tty_audit_buf *buf; struct tty_audit_buf *buf;
dev_t dev; dev_t dev;
unsigned long flags;
spin_lock_irqsave(&current->sighand->siglock, flags);
buf = current->signal->tty_audit_buf;
if (buf)
atomic_inc(&buf->count);
spin_unlock_irqrestore(&current->sighand->siglock, flags);
dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index; dev = MKDEV(tty->driver->major, tty->driver->minor_start) + tty->index;
buf = current->signal->tty_audit_buf;
if (buf) { if (buf) {
mutex_lock(&buf->mutex); mutex_lock(&buf->mutex);
if (buf->dev == dev) if (buf->dev == dev)
tty_audit_buf_push(buf); tty_audit_buf_push(buf);
mutex_unlock(&buf->mutex); mutex_unlock(&buf->mutex);
tty_audit_buf_put(buf);
} }
if (audit_enabled && (current->signal->audit_tty & AUDIT_TTY_ENABLE)) { if (audit_enabled && (current->signal->audit_tty & AUDIT_TTY_ENABLE)) {
@ -175,23 +160,15 @@ void tty_audit_tiocsti(struct tty_struct *tty, char ch)
int tty_audit_push(void) int tty_audit_push(void)
{ {
struct tty_audit_buf *buf; struct tty_audit_buf *buf;
unsigned long flags;
if (~current->signal->audit_tty & AUDIT_TTY_ENABLE) if (~current->signal->audit_tty & AUDIT_TTY_ENABLE)
return -EPERM; return -EPERM;
spin_lock_irqsave(&current->sighand->siglock, flags);
buf = current->signal->tty_audit_buf; buf = current->signal->tty_audit_buf;
if (buf)
atomic_inc(&buf->count);
spin_unlock_irqrestore(&current->sighand->siglock, flags);
if (buf) { if (buf) {
mutex_lock(&buf->mutex); mutex_lock(&buf->mutex);
tty_audit_buf_push(buf); tty_audit_buf_push(buf);
mutex_unlock(&buf->mutex); mutex_unlock(&buf->mutex);
tty_audit_buf_put(buf);
} }
return 0; return 0;
} }
@ -207,15 +184,9 @@ static struct tty_audit_buf *tty_audit_buf_get(void)
struct tty_audit_buf *buf, *buf2; struct tty_audit_buf *buf, *buf2;
unsigned long flags; unsigned long flags;
buf = NULL;
buf2 = NULL;
spin_lock_irqsave(&current->sighand->siglock, flags);
buf = current->signal->tty_audit_buf; buf = current->signal->tty_audit_buf;
if (buf) { if (buf)
atomic_inc(&buf->count); return buf;
goto out;
}
spin_unlock_irqrestore(&current->sighand->siglock, flags);
buf2 = tty_audit_buf_alloc(); buf2 = tty_audit_buf_alloc();
if (buf2 == NULL) { if (buf2 == NULL) {
@ -230,9 +201,6 @@ static struct tty_audit_buf *tty_audit_buf_get(void)
buf = buf2; buf = buf2;
buf2 = NULL; buf2 = NULL;
} }
atomic_inc(&buf->count);
/* Fall through */
out:
spin_unlock_irqrestore(&current->sighand->siglock, flags); spin_unlock_irqrestore(&current->sighand->siglock, flags);
if (buf2) if (buf2)
tty_audit_buf_free(buf2); tty_audit_buf_free(buf2);
@ -289,5 +257,4 @@ void tty_audit_add_data(struct tty_struct *tty, const void *data, size_t size)
tty_audit_buf_push(buf); tty_audit_buf_push(buf);
} while (size != 0); } while (size != 0);
mutex_unlock(&buf->mutex); mutex_unlock(&buf->mutex);
tty_audit_buf_put(buf);
} }