[patch 037/100] dm io: make sync_io uninterruptible

Chris Wright
2009-04-23T07:39:43Z

[-- Attachment #1: dm-io-make-sync_io-uninterruptible.patch --]
[-- Type: text/plain, Size: 1545 bytes --]

-stable review patch. If anyone has any objections, please let us know.
---------------------

From: Mikulas Patocka <mpatocka@redhat.com>

upstream commit: b64b6bf4fd8b678a9f8477c11773c38a0a246a6d

If someone sends signal to a process performing synchronous dm-io call,
the kernel may crash.

The function sync_io attempts to exit with -EINTR if it has pending signal,
however the structure "io" is allocated on stack, so already submitted io
requests end up touching unallocated stack space and corrupting kernel memory.

sync_io sets its state to TASK_UNINTERRUPTIBLE, so the signal can't break out
of io_schedule() --- however, if the signal was pending before sync_io entered
while (1) loop, the corruption of kernel memory will happen.

There is no way to cancel in-progress IOs, so the best solution is to ignore
signals at this point.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
drivers/md/dm-io.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -370,16 +370,13 @@ static int sync_io(struct dm_io_client *
while (1) {
set_current_state(TASK_UNINTERRUPTIBLE);

- if (!atomic_read(&io.count) || signal_pending(current))
+ if (!atomic_read(&io.count))
break;

io_schedule();
}
set_current_state(TASK_RUNNING);

- if (atomic_read(&io.count))
- return -EINTR;
-
if (error_bits)
*error_bits = io.error_bits;