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

Commit Message

Xiaohui Zhang Dec. 8, 2020, 12:45 p.m. UTC

From: Zhang Xiaohui <[e-mail]>

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().

Signed-off-by: Zhang Xiaohui <[e-mail]>
---
 drivers/net/wireless/marvell/mwifiex/scan.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Kalle Valo Dec. 8, 2020, 2:29 p.m. UTC | #1

Xiaohui Zhang <[e-mail]> writes:

> From: Zhang Xiaohui <[e-mail]>
>
> 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().
>
> Signed-off-by: Zhang Xiaohui <[e-mail]>
> ---
>  drivers/net/wireless/marvell/mwifiex/scan.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index c2a685f63..b1d90678f 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -930,6 +930,8 @@ mwifiex_config_scan(struct mwifiex_private *priv,
>  				    "DIRECT-", 7))
>  				wildcard_ssid_tlv->max_ssid_length = 0xfe;
>  
> +			if (ssid_len > 1)
> +				ssid_len = 1;
>  			memcpy(wildcard_ssid_tlv->ssid,
>  			       user_scan_in->ssid_list[i].ssid, ssid_len);

min_t()?

Julian Calaby Dec. 9, 2020, 12:36 a.m. UTC | #2

Hi Xiaohui,

On Wed, Dec 9, 2020 at 12:07 AM Xiaohui Zhang <[e-mail]> wrote:
>
> From: Zhang Xiaohui <[e-mail]>
>
> 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().
>
> Signed-off-by: Zhang Xiaohui <[e-mail]>
> ---
>  drivers/net/wireless/marvell/mwifiex/scan.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index c2a685f63..b1d90678f 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -930,6 +930,8 @@ mwifiex_config_scan(struct mwifiex_private *priv,
>                                     "DIRECT-", 7))
>                                 wildcard_ssid_tlv->max_ssid_length = 0xfe;
>
> +                       if (ssid_len > 1)
> +                               ssid_len = 1;
>                         memcpy(wildcard_ssid_tlv->ssid,
>                                user_scan_in->ssid_list[i].ssid, ssid_len);

Can ssid_len ever be 0 here?

If it can't, should we just set ssid_len to 1 unconditionally?

If it can, should we just skip the memcpy as it won't do anything?

Thanks,

Peter Seiderer Jan. 9, 2021, 3:08 p.m. UTC | #3

Hello Zhang,

On Tue,  8 Dec 2020 20:45:23 +0800, Xiaohui Zhang <[e-mail]> wrote:

> From: Zhang Xiaohui <[e-mail]>
>
> 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().
>
> Signed-off-by: Zhang Xiaohui <[e-mail]>
> ---
>  drivers/net/wireless/marvell/mwifiex/scan.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> index c2a685f63..b1d90678f 100644
> --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> @@ -930,6 +930,8 @@ mwifiex_config_scan(struct mwifiex_private *priv,
>  				    "DIRECT-", 7))
>  				wildcard_ssid_tlv->max_ssid_length = 0xfe;
>
> +			if (ssid_len > 1)
> +				ssid_len = 1;

Why do your believe the available size is only '1'? A SSID is expected
to be of size IEEE80211_MAX_SSID_LE/32 and the wildcard_ssid_tlv pointer
is casted from tlv_pos (some lines above) which is a pointer/index into
scan_cfg_out->tlv_buf...

And the define (line 44) indicates there should be enough space for a SSID:

  42 /* Memory needed to store a max number/size WildCard SSID TLV for a firmware
  43         scan */
  44 #define WILDCARD_SSID_TLV_MAX_SIZE  \
  45         (MWIFIEX_MAX_SSID_LIST_LENGTH *                                 \
  46                 (sizeof(struct mwifiex_ie_types_wildcard_ssid_params)   \
  47                         + IEEE80211_MAX_SSID_LEN))

For sure something to improve here instead of using a confusing 'u8 ssid[1]'
in struct mwifiex_ie_types_wildcard_ssid_params...

Regards,
Peter

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

Brian Norris Jan. 11, 2021, 6:51 p.m. UTC | #4

(Note: this is version 1; there's a later version posted, which does
not have a v2 tag...)

https://lore.kernel.org/linux-wireless/[e-mail]/

On Sat, Jan 9, 2021 at 7:11 AM Peter Seiderer <[e-mail]> wrote:
> On Tue,  8 Dec 2020 20:45:23 +0800, Xiaohui Zhang <[e-mail]> wrote:
> > From: Zhang Xiaohui <[e-mail]>
> > 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().
> >
> > Signed-off-by: Zhang Xiaohui <[e-mail]>
> > ---
> >  drivers/net/wireless/marvell/mwifiex/scan.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
> > index c2a685f63..b1d90678f 100644
> > --- a/drivers/net/wireless/marvell/mwifiex/scan.c
> > +++ b/drivers/net/wireless/marvell/mwifiex/scan.c
> > @@ -930,6 +930,8 @@ mwifiex_config_scan(struct mwifiex_private *priv,
> >                                   "DIRECT-", 7))
> >                               wildcard_ssid_tlv->max_ssid_length = 0xfe;
> >
> > +                     if (ssid_len > 1)
> > +                             ssid_len = 1;
>
> Why do your believe the available size is only '1'? A SSID is expected
> to be of size IEEE80211_MAX_SSID_LE/32 and the wildcard_ssid_tlv pointer
> is casted from tlv_pos (some lines above) which is a pointer/index into
> scan_cfg_out->tlv_buf...

I pointed out this discrepancy already, taking a slightly different approach:

https://lore.kernel.org/linux-wireless/[e-mail]/

> And the define (line 44) indicates there should be enough space for a SSID:
>
>   42 /* Memory needed to store a max number/size WildCard SSID TLV for a firmware
>   43         scan */
>   44 #define WILDCARD_SSID_TLV_MAX_SIZE  \
>   45         (MWIFIEX_MAX_SSID_LIST_LENGTH *                                 \
>   46                 (sizeof(struct mwifiex_ie_types_wildcard_ssid_params)   \
>   47                         + IEEE80211_MAX_SSID_LEN))

Ah, good catch. So this may not be a true overflow issue at all, even
if it's confusing and bad code. The "problem" is that this piece of
the struct is variable-length, and unless we're going to dynamically
resize/reallocate the whole buffer, we have to assume the initial
allocation was large enough (and per your note, it is).

> For sure something to improve here instead of using a confusing 'u8 ssid[1]'
> in struct mwifiex_ie_types_wildcard_ssid_params...

Yep.

Brian

Patch

diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
index c2a685f63..b1d90678f 100644
--- a/drivers/net/wireless/marvell/mwifiex/scan.c
+++ b/drivers/net/wireless/marvell/mwifiex/scan.c
@@ -930,6 +930,8 @@  mwifiex_config_scan(struct mwifiex_private *priv,
 				    "DIRECT-", 7))
 				wildcard_ssid_tlv->max_ssid_length = 0xfe;
 
+			if (ssid_len > 1)
+				ssid_len = 1;
 			memcpy(wildcard_ssid_tlv->ssid,
 			       user_scan_in->ssid_list[i].ssid, ssid_len);