[PATCH] Fix read buffer overflow in delta-ipc

From: Andi Kleen <andi@firstfloor.org>
To: linux-kernel@vger.kernel.org
Cc: akpm@linux-foundation.org, Andi Kleen <ak@linux.intel.com>,
	hugues.fruchet@st.com, mchehab@s-opensource.com
Subject: [PATCH] Fix read buffer overflow in delta-ipc
Date: Thu, 21 Dec 2017 16:12:12 -0800	[thread overview]
Message-ID: <20171222001212.1850-1-andi@firstfloor.org> (raw)

From: Andi Kleen <ak@linux.intel.com>

The single caller passes a string to delta_ipc_open, which copies with a
fixed size larger than the string. So it copies some random data after
the original string the ro segment.

If the string was at the end of a page it may fault.

Just copy the string with a normal strcpy after clearing the field.

Found by a LTO build (which errors out)
because the compiler inlines the functions and can resolve
the string sizes and triggers the compile time checks in memcpy.

In function ‘memcpy’,
    inlined from ‘delta_ipc_open.constprop’ at linux/drivers/media/platform/sti/delta/delta-ipc.c:178:0,
    inlined from ‘delta_mjpeg_ipc_open’ at linux/drivers/media/platform/sti/delta/delta-mjpeg-dec.c:227:0,
    inlined from ‘delta_mjpeg_decode’ at linux/drivers/media/platform/sti/delta/delta-mjpeg-dec.c:403:0:
/home/andi/lsrc/linux/include/linux/string.h:337:0: error: call to ‘__read_overflow2’ declared with attribute error: detected read beyond size of object passed as 2nd parameter
    __read_overflow2();

Cc: hugues.fruchet@st.com
Cc: mchehab@s-opensource.com
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 drivers/media/platform/sti/delta/delta-ipc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/platform/sti/delta/delta-ipc.c b/drivers/media/platform/sti/delta/delta-ipc.c
index 41e4a4c259b3..b6c256e3ceb6 100644
--- a/drivers/media/platform/sti/delta/delta-ipc.c
+++ b/drivers/media/platform/sti/delta/delta-ipc.c
@@ -175,8 +175,8 @@ int delta_ipc_open(struct delta_ctx *pctx, const char *name,
 	msg.ipc_buf_size = ipc_buf_size;
 	msg.ipc_buf_paddr = ctx->ipc_buf->paddr;
 
-	memcpy(msg.name, name, sizeof(msg.name));
-	msg.name[sizeof(msg.name) - 1] = 0;
+	memset(msg.name, 0, sizeof(msg.name));
+	strcpy(msg.name, name);
 
 	msg.param_size = param->size;
 	memcpy(ctx->ipc_buf->vaddr, param->data, msg.param_size);
-- 
2.15.0
