Re: [PATCH 1/1] mwifiex: Fix possible buffer overflows in mwifiex_config_scan

Brian Norris [off-list ref] writes:

On Tue, Dec 8, 2020 at 7:14 AM Xiaohui Zhang [off-list ref] wrote:

quoted

From: Zhang Xiaohui <redacted>

mwifiex_config_scan() calls memcpy() without checking
the destination size may trigger a buffer overflower,
which a local user could use to cause denial of service
or the execution of arbitrary code.
Fix it by putting the length check before calling memcpy().

^^ That's not really what you're doing any more, for the record. But
then, describing "what" is not really the point of a commit message
(that's what the code is for), so maybe that's not that important.

quoted

Signed-off-by: Zhang Xiaohui <redacted>
---
 drivers/net/wireless/marvell/mwifiex/scan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
index c2a685f63..34293fd80 100644
--- a/drivers/net/wireless/marvell/mwifiex/scan.c
+++ b/drivers/net/wireless/marvell/mwifiex/scan.c

@@ -931,7 +931,7 @@ mwifiex_config_scan(struct mwifiex_private *priv,
                                wildcard_ssid_tlv->max_ssid_length = 0xfe;

                        memcpy(wildcard_ssid_tlv->ssid,
-                              user_scan_in->ssid_list[i].ssid, ssid_len);
+                              user_scan_in->ssid_list[i].ssid, min_t(u32, ssid_len, 1));

This *looks* like it should be wrong, because SSIDs are clearly longer
than 1 byte in many cases, but you *are* right that this is what the
struct is defined as:

struct mwifiex_ie_types_wildcard_ssid_params {
...
    u8 ssid[1];
};

This feels like something that could use some confirmation from
NXP/ex-Marvell folks if possible, but if not that, at least some
creative testing. Did you actually test this patch, to make sure
non-wildcard scans still work?

Also, even if this is correct, it seems like it would be more correct
to use 'sizeof(wildcard_ssid_tlv->ssid)' instead of a magic number 1.

Xiaohui, please respond to Brian's comments. If you ignore review
comments I have a hard time trusting your patches.

Also when you submit a new version you should mark it as v2. See more in
the wiki link below.

-- 
https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches