linux-kernel - [PATCH] crypto: qat: fix double free in qat_uclo_create_batch_init

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Message-Id: <20200713140634.14730-1-trix@redhat.com>
Date:   Mon, 13 Jul 2020 07:06:34 -0700
From:   trix@...hat.com
To:     giovanni.cabiddu@...el.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, wojciech.ziemba@...el.com,
        karen.xiang@...el.com, bruce.w.allan@...el.com, bo.cui@...el.com,
        pingchaox.yang@...el.com
Cc:     qat-linux@...el.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Tom Rix <trix@...hat.com>
Subject: [PATCH] crypto: qat: fix double free in qat_uclo_create_batch_init_list

From: Tom Rix <trix@...hat.com>

clang static analysis flags this error

qat_uclo.c:297:3: warning: Attempt to free released memory
  [unix.Malloc]
                kfree(*init_tab_base);
                ^~~~~~~~~~~~~~~~~~~~~

When input *init_tab_base is null, the function allocates memory for
the head of the list.  When there is problem allocating other list
elements the list is unwound and freed.  Then a check is made if the
list head was allocated and is also freed.

Keeping track of the what may need to be freed is the variable 'tail_old'.
The unwinding/freeing block is

	while (tail_old) {
		mem_init = tail_old->next;
		kfree(tail_old);
		tail_old = mem_init;
	}

The problem is that the first element of tail_old is also what was
allocated for the list head

		init_header = kzalloc(sizeof(*init_header), GFP_KERNEL);
		...
		*init_tab_base = init_header;
		flag = 1;
	}
	tail_old = init_header;

So *init_tab_base/init_header are freed twice.

There is another problem.
When the input *init_tab_base is non null the tail_old is calculated by
traveling down the list to first non null entry.

	tail_old = init_header;
	while (tail_old->next)
		tail_old = tail_old->next;

When the unwinding free happens, the last entry of the input list will
be freed.

So the freeing needs a general changed.
If locally allocated the first element of tail_old is freed, else it
is skipped.  As a bit of cleanup, reset *init_tab_base if it came in
as null.

Fixes: b4b7e67c917f ("crypto: qat - Intel(R) QAT ucode part of fw loader")

Signed-off-by: Tom Rix <trix@...hat.com>
---
 drivers/crypto/qat/qat_common/qat_uclo.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/qat/qat_common/qat_uclo.c b/drivers/crypto/qat/qat_common/qat_uclo.c
index 4cc1f436b075..bff759e2f811 100644
--- a/drivers/crypto/qat/qat_common/qat_uclo.c
+++ b/drivers/crypto/qat/qat_common/qat_uclo.c
@@ -288,13 +288,18 @@ static int qat_uclo_create_batch_init_list(struct icp_qat_fw_loader_handle
 	}
 	return 0;
 out_err:
+	/* Do not free the list head unless we allocated it. */
+	tail_old = tail_old->next;
+	if (flag) {
+		kfree(*init_tab_base);
+		*init_tab_base = NULL;
+	}
+
 	while (tail_old) {
 		mem_init = tail_old->next;
 		kfree(tail_old);
 		tail_old = mem_init;
 	}
-	if (flag)
-		kfree(*init_tab_base);
 	return -ENOMEM;
 }
 
-- 
2.18.1