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From:   Lv Yunlong <lyl2019@mail.ustc.edu.cn>
To:     ogabbay@kernel.org, arnd@arndb.de, obitton@habana.ai
Cc:     linux-kernel@vger.kernel.org, Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Subject: [PATCH] habanalabs/gaudi: Fix a potential use after free in gaudi_memset_device_memory
Date:   Mon, 26 Apr 2021 06:43:46 -0700
Message-Id: <20210426134346.6126-1-lyl2019@mail.ustc.edu.cn>
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Our code analyzer reported a uaf.

In gaudi_memset_device_memory, cb is get via hl_cb_kernel_create()
with 2 refcount.
If hl_cs_allocate_job() failed, the execution runs into release_cb
branch. One ref of cb is dropped by hl_cb_put(cb) and could be freed
if other thread also drops one ref. Then cb is used by cb->id later,
which is a potential uaf.

My patch add a variable 'id' to accept the value of cb->id before the
hl_cb_put(cb) is called, to avoid the potential uaf.

Fixes: 423815bf02e25 ("habanalabs/gaudi: remove PCI access to SM block")
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
---
 drivers/misc/habanalabs/gaudi/gaudi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/habanalabs/gaudi/gaudi.c b/drivers/misc/habanalabs/gaudi/gaudi.c
index 9152242778f5..ecdedd87f8cc 100644
--- a/drivers/misc/habanalabs/gaudi/gaudi.c
+++ b/drivers/misc/habanalabs/gaudi/gaudi.c
@@ -5546,6 +5546,7 @@ static int gaudi_memset_device_memory(struct hl_device *hdev, u64 addr,
 	struct hl_cs_job *job;
 	u32 cb_size, ctl, err_cause;
 	struct hl_cb *cb;
+	u64 id;
 	int rc;
 
 	cb = hl_cb_kernel_create(hdev, PAGE_SIZE, false);
@@ -5612,8 +5613,9 @@ static int gaudi_memset_device_memory(struct hl_device *hdev, u64 addr,
 	}
 
 release_cb:
+	id = cb->id;
 	hl_cb_put(cb);
-	hl_cb_destroy(hdev, &hdev->kernel_cb_mgr, cb->id << PAGE_SHIFT);
+	hl_cb_destroy(hdev, &hdev->kernel_cb_mgr, id << PAGE_SHIFT);
 
 	return rc;
 }
-- 
2.25.1