[PATCH 2/6] powerpc/spufs: don't leak kernel stack via spu_run

[Junrui Luo via B4 Relay <devnull+moonafterrain.outlook.com@kernel.org>]

From: Junrui Luo <moonafterrain@outlook.com>

do_spu_run() hands the address of an uninitialized local to
spufs_run_spu() and then copies it out unconditionally:

	u32 npc, status;
	...
	ret = spufs_run_spu(i->i_ctx, &npc, &status);
	...
	if (ustatus && put_user(status, ustatus))
		ret = -EFAULT;

spufs_run_spu() writes through that pointer at exactly one place, the
"out:" label, and two of its exits never reach it: the interruptible
acquisition of ctx->run_mutex returns -ERESTARTSYS directly, and a
failed spu_acquire() jumps to "out_unlock", which sits just after the
assignment.

Initialize status to 0, which is what userspace would have observed had
the assignment been reached anyway: spufs_run_spu() resets
ctx->event_return to 0 on entry, and 0 is the "no events pending" value
for this word.

Fixes: 67207b9664a8 ("[PATCH] spufs: The SPU file system, base")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
---
 arch/powerpc/platforms/cell/spufs/syscalls.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/cell/spufs/syscalls.c b/arch/powerpc/platforms/cell/spufs/syscalls.c
index ea4ba1b6ce6a..549fcfbbc140 100644
--- a/arch/powerpc/platforms/cell/spufs/syscalls.c
+++ b/arch/powerpc/platforms/cell/spufs/syscalls.c
@@ -37,7 +37,7 @@ static long do_spu_run(struct file *filp,
 {
 	long ret;
 	struct spufs_inode_info *i;
-	u32 npc, status;
+	u32 npc, status = 0;
 
 	ret = -EFAULT;
 	if (get_user(npc, unpc))

-- 
2.51.2