From 638570b54346f140bc09b986d93e76025d35180f Mon Sep 17 00:00:00 2001 From: Stefan Richter Date: Sun, 26 Oct 2008 12:03:37 +0100 Subject: [PATCH] ieee1394: raw1394: fix possible deadlock in multithreaded clients Regression in 2.6.28-rc1: When I added the new state_mutex which prevents corruption of raw1394's internal state when accessed by multithreaded client applications, the following possible though highly unlikely deadlock slipped in: Thread A: Thread B: - acquire mmap_sem - raw1394_write() or raw1394_ioctl() - raw1394_mmap() - acquire state_mutex - acquire state_mutex - copy_to/from_user(), possible page fault: acquire mmap_sem The simplest fix is to use mutex_trylock() instead of mutex_lock() in raw1394_mmap(). This changes the behavior under contention in a way which is visible to userspace clients. However, since multithreaded access was entirely buggy before state_mutex was added and libraw1394's documentation advised application programmers to use a handle only in a single thread, this change in behaviour should not be an issue in practice at all. Since we have to use mutex_trylock() in raw1394_mmap() regardless whether /dev/raw1394 was opened with O_NONBLOCK or not, we now use mutex_trylock() unconditionally everywhere for state_mutex, just to have consistent behavior. Reported-by: Johannes Weiner Signed-off-by: Stefan Richter --- drivers/ieee1394/raw1394.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/ieee1394/raw1394.c b/drivers/ieee1394/raw1394.c index 2cf4ae75bec..4bdfff0a919 100644 --- a/drivers/ieee1394/raw1394.c +++ b/drivers/ieee1394/raw1394.c @@ -2268,7 +2268,8 @@ static ssize_t raw1394_write(struct file *file, const char __user * buffer, return -EFAULT; } - mutex_lock(&fi->state_mutex); + if (!mutex_trylock(&fi->state_mutex)) + return -EAGAIN; switch (fi->state) { case opened: @@ -2548,7 +2549,8 @@ static int raw1394_mmap(struct file *file, struct vm_area_struct *vma) struct file_info *fi = file->private_data; int ret; - mutex_lock(&fi->state_mutex); + if (!mutex_trylock(&fi->state_mutex)) + return -EAGAIN; if (fi->iso_state == RAW1394_ISO_INACTIVE) ret = -EINVAL; @@ -2669,7 +2671,8 @@ static long raw1394_ioctl(struct file *file, unsigned int cmd, break; } - mutex_lock(&fi->state_mutex); + if (!mutex_trylock(&fi->state_mutex)) + return -EAGAIN; switch (fi->iso_state) { case RAW1394_ISO_INACTIVE: -- 2.41.1