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


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