linux-kernel - [PATCH 1/2] staging: comedi: ni_routes: fix null dereference in ni_find_route

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Message-Id: <20200114182532.132058-2-abbotti@mev.co.uk>
Date:   Tue, 14 Jan 2020 18:25:31 +0000
From:   Ian Abbott <abbotti@....co.uk>
To:     devel@...verdev.osuosl.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ian Abbott <abbotti@....co.uk>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "Spencer E . Olson" <olsonse@...ch.edu>
Subject: [PATCH 1/2] staging: comedi: ni_routes: fix null dereference in ni_find_route_source()

In `ni_find_route_source()`, `tables->route_values` gets dereferenced.
However it is possible that `tables->route_values` is `NULL`, leading to
a null pointer dereference.  `tables->route_values` will be `NULL` if
the call to `ni_assign_device_routes()` during board initialization
returned an error due to missing device family routing information or
missing board-specific routing information.  For example, there is
currently no board-specific routing information provided for the
PCIe-6251 board and several other boards, so those are affected by this
bug.

The bug is triggered when `ni_find_route_source()` is called via
`ni_check_trigger_arg()` or `ni_check_trigger_arg_roffs()` when checking
the arguments for setting up asynchronous commands.  Fix it by returning
`-EINVAL` if `tables->route_values` is `NULL`.

Even with this fix, setting up asynchronous commands to use external
trigger sources for boards with missing routing information will still
fail gracefully.  Since `ni_find_route_source()` only depends on the
device family routing information, it would be better if that was made
available even if the board-specific routing information is missing.
That will be addressed by another patch.

Fixes: 4bb90c87abbe ("staging: comedi: add interface to ni routing table information")
Cc: <stable@...r.kernel.org> # 4.20+
Cc: Spencer E. Olson <olsonse@...ch.edu>
Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
 drivers/staging/comedi/drivers/ni_routes.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/staging/comedi/drivers/ni_routes.c b/drivers/staging/comedi/drivers/ni_routes.c
index 673d732dcb8f..9627bd1d2a78 100644
--- a/drivers/staging/comedi/drivers/ni_routes.c
+++ b/drivers/staging/comedi/drivers/ni_routes.c
@@ -487,6 +487,9 @@ int ni_find_route_source(const u8 src_sel_reg_value, int dest,
 {
 	int src;

+	if (!tables->route_values)
+		return -EINVAL;
+
 	dest = B(dest); /* subtract NI names offset */
 	/* ensure we are not going to under/over run the route value table */
 	if (dest < 0 || dest >= NI_NUM_NAMES)
-- 
2.24.1