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

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

[Xiaohui Zhang]

From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>

mwifiex_uap_bss_param_prepare() 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 <ruc_zhangxiaohui@163.com>
---
 drivers/net/wireless/marvell/mwifiex/uap_cmd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
index b48a85d79..fb937c7ee 100644
--- a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
+++ b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
@@ -496,13 +496,16 @@ mwifiex_uap_bss_param_prepare(u8 *tlv, void *cmd_buf, u16 *param_size)
 	struct mwifiex_ie_types_wmmcap *wmm_cap;
 	struct mwifiex_uap_bss_param *bss_cfg = cmd_buf;
 	int i;
+	int ssid_size;
 	u16 cmd_size = *param_size;
 
 	if (bss_cfg->ssid.ssid_len) {
 		ssid = (struct host_cmd_tlv_ssid *)tlv;
 		ssid->header.type = cpu_to_le16(TLV_TYPE_UAP_SSID);
 		ssid->header.len = cpu_to_le16((u16)bss_cfg->ssid.ssid_len);
-		memcpy(ssid->ssid, bss_cfg->ssid.ssid, bss_cfg->ssid.ssid_len);
+		ssid_size = bss_cfg->ssid.ssid_len > strlen(ssid->ssid) ?
+				strlen(ssid->ssid) : bss_cfg->ssid.ssid_len;
+		memcpy(ssid->ssid, bss_cfg->ssid.ssid, ssid_size);
 		cmd_size += sizeof(struct mwifiex_ie_types_header) +
 			    bss_cfg->ssid.ssid_len;
 		tlv += sizeof(struct mwifiex_ie_types_header) +
-- 
2.17.1

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

[Kalle Valo]

Xiaohui Zhang <ruc_zhangxiaohui@163.com> writes:

> From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
>
> mwifiex_uap_bss_param_prepare() 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 <ruc_zhangxiaohui@163.com>
> ---
>  drivers/net/wireless/marvell/mwifiex/uap_cmd.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> index b48a85d79..fb937c7ee 100644
> --- a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> +++ b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> @@ -496,13 +496,16 @@ mwifiex_uap_bss_param_prepare(u8 *tlv, void *cmd_buf, u16 *param_size)
>  	struct mwifiex_ie_types_wmmcap *wmm_cap;
>  	struct mwifiex_uap_bss_param *bss_cfg = cmd_buf;
>  	int i;
> +	int ssid_size;
>  	u16 cmd_size = *param_size;
>  
>  	if (bss_cfg->ssid.ssid_len) {
>  		ssid = (struct host_cmd_tlv_ssid *)tlv;
>  		ssid->header.type = cpu_to_le16(TLV_TYPE_UAP_SSID);
>  		ssid->header.len = cpu_to_le16((u16)bss_cfg->ssid.ssid_len);
> -		memcpy(ssid->ssid, bss_cfg->ssid.ssid, bss_cfg->ssid.ssid_len);
> +		ssid_size = bss_cfg->ssid.ssid_len > strlen(ssid->ssid) ?
> +				strlen(ssid->ssid) : bss_cfg->ssid.ssid_len;
> +		memcpy(ssid->ssid, bss_cfg->ssid.ssid, ssid_size);

I think using min_t() is cleaner. Then you would not need to add a
temporary variable.

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

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

[Brian Norris]

(FWIW, this author's mail has been routed to my spam mailbox. That's
partly my fault and/or my "choice" of mail provider, but that's why I
only see these once Kalle replies to them.)

On Tue, Dec 8, 2020 at 8:03 AM Xiaohui Zhang <ruc_zhangxiaohui@163.com> wrote:
>
> From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
>
> mwifiex_uap_bss_param_prepare() 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 <ruc_zhangxiaohui@163.com>
> ---
>  drivers/net/wireless/marvell/mwifiex/uap_cmd.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> index b48a85d79..937c75e89 100644
> --- a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> +++ b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
> @@ -502,7 +502,8 @@ mwifiex_uap_bss_param_prepare(u8 *tlv, void *cmd_buf, u16 *param_size)
>                 ssid = (struct host_cmd_tlv_ssid *)tlv;
>                 ssid->header.type = cpu_to_le16(TLV_TYPE_UAP_SSID);
>                 ssid->header.len = cpu_to_le16((u16)bss_cfg->ssid.ssid_len);
> -               memcpy(ssid->ssid, bss_cfg->ssid.ssid, bss_cfg->ssid.ssid_len);
> +               memcpy(ssid->ssid, bss_cfg->ssid.ssid,
> +                      min_t(u32, bss_cfg->ssid.ssid_len, strlen(ssid->ssid)));

This strlen() check makes no sense to me. We are *writing* to
ssid->ssid, so its initial contents are either zero or garbage --
strlen() will either give a zero or unpredictable value. I'm pretty
sure that's not what you intend.

On the other hand, it's hard to determine what the proper bound here
*should* be. This 'ssid' struct is really just a pointer into
mwifiex_cmd_uap_sys_config()'s uap_sys_config (struct
host_cmd_ds_sys_config), which doesn't have any defined length -- its
length is only given by way of its surrounding buffers/structs.
Altogether, the code is hard to reason about.

Anyway, this patch is wrong, so NAK.

Brian

>                 cmd_size += sizeof(struct mwifiex_ie_types_header) +
>                             bss_cfg->ssid.ssid_len;
>                 tlv += sizeof(struct mwifiex_ie_types_header) +
> --
> 2.17.1
>

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

[Kalle Valo]

Xiaohui Zhang <ruc_zhangxiaohui@163.com> writes:

> From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>
>
> mwifiex_uap_bss_param_prepare() 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 <ruc_zhangxiaohui@163.com>

When you submit a new version mark it as v2:

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

But this is just for the future, no need to resend because of this.

-- 
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[PATCH 1/1] mwifiex: Fix possible buffer overflows in mwifiex_uap_bss_param_prepare

[Xiaohui Zhang]

From: Zhang Xiaohui <ruc_zhangxiaohui@163.com>

mwifiex_uap_bss_param_prepare() 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 <ruc_zhangxiaohui@163.com>
---
 drivers/net/wireless/marvell/mwifiex/uap_cmd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
index b48a85d79..937c75e89 100644
--- a/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
+++ b/drivers/net/wireless/marvell/mwifiex/uap_cmd.c
@@ -502,7 +502,8 @@ mwifiex_uap_bss_param_prepare(u8 *tlv, void *cmd_buf, u16 *param_size)
 		ssid = (struct host_cmd_tlv_ssid *)tlv;
 		ssid->header.type = cpu_to_le16(TLV_TYPE_UAP_SSID);
 		ssid->header.len = cpu_to_le16((u16)bss_cfg->ssid.ssid_len);
-		memcpy(ssid->ssid, bss_cfg->ssid.ssid, bss_cfg->ssid.ssid_len);
+		memcpy(ssid->ssid, bss_cfg->ssid.ssid,
+		       min_t(u32, bss_cfg->ssid.ssid_len, strlen(ssid->ssid)));
 		cmd_size += sizeof(struct mwifiex_ie_types_header) +
 			    bss_cfg->ssid.ssid_len;
 		tlv += sizeof(struct mwifiex_ie_types_header) +
-- 
2.17.1