[Patch 09/12] GRU - fix potential use-after-free when purging GRU tlbs

[steiner@sgi.com]

[-- Attachment #1: uv_gru_flush_tlb_fix --]
[-- Type: text/plain, Size: 1354 bytes --]

From: Jack Steiner <steiner@sgi.com>

Fix potential SGI GRU bug that could cause a use-after-free. If one
thread in a task is flushing the GRU and another thread destroys the GRU context,
there is the potential to access a table after it has been freed.

Copy the gms pointer to a local variable before unlocking the gts table.
Note that no refcnt is needed for the gms - the reference is held indirectly
by the task's mm_struct.

Signed-off-by: Jack Steiner <steiner@sgi.com>

---
 drivers/misc/sgi-gru/grufault.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux/drivers/misc/sgi-gru/grufault.c
===================================================================
--- linux.orig/drivers/misc/sgi-gru/grufault.c	2009-06-05 15:33:05.000000000 -0500
+++ linux/drivers/misc/sgi-gru/grufault.c	2009-06-05 15:33:05.000000000 -0500
@@ -706,6 +706,7 @@ int gru_user_flush_tlb(unsigned long arg
 {
 	struct gru_thread_state *gts;
 	struct gru_flush_tlb_req req;
+	struct gru_mm_struct *gms;
 
 	STAT(user_flush_tlb);
 	if (copy_from_user(&req, (void __user *)arg, sizeof(req)))
@@ -718,8 +719,9 @@ int gru_user_flush_tlb(unsigned long arg
 	if (!gts)
 		return -EINVAL;
 
-	gru_flush_tlb_range(gts->ts_gms, req.vaddr, req.len);
+	gms = gts->ts_gms;
 	gru_unlock_gts(gts);
+	gru_flush_tlb_range(gms, req.vaddr, req.len);
 
 	return 0;
 }