diff mbox series

wifi: mwifiex: Fix memcpy() field-spanning write warning in mwifiex_config_scan()

Message ID 20240917150938.843879-1-alpernebiyasak@gmail.com
State New
Headers show
Series wifi: mwifiex: Fix memcpy() field-spanning write warning in mwifiex_config_scan() | expand

Commit Message

Alper Nebi Yasak Sept. 17, 2024, 3:08 p.m. UTC 
Replace one-element array with a flexible-array member in `struct
mwifiex_ie_types_wildcard_ssid_params` to fix the following warning
on a MT8173 Chromebook (mt8173-elm-hana):

[  356.775250] ------------[ cut here ]------------
[  356.784543] memcpy: detected field-spanning write (size 6) of single field "wildcard_ssid_tlv->ssid" at drivers/net/wireless/marvell/mwifiex/scan.c:904 (size 1)
[  356.813403] WARNING: CPU: 3 PID: 742 at drivers/net/wireless/marvell/mwifiex/scan.c:904 mwifiex_scan_networks+0x4fc/0xf28 [mwifiex]

The "(size 6)" above is exactly the length of the SSID of the network
this device was connected to. The source of the warning looks like:

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

Also adjust a #define that uses sizeof() on this struct to keep the
value same as before.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
---
I found these relevant patches that modify other such arrays, where the
second one removes a -1 from some sizeof() calculation:

https://lore.kernel.org/lkml/Y9xkECG3uTZ6T1dN@work/T/#u
https://lore.kernel.org/lkml/ZsZa5xRcsLq9D+RX@elsanto/T/#u

So I think we need the +1 to keep things same. But it appears to work
fine without it, so I'm not sure. Maybe it should've had a -1 before
that I would remove with this?

 drivers/net/wireless/marvell/mwifiex/fw.h   | 2 +-
 drivers/net/wireless/marvell/mwifiex/scan.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)


base-commit: 4f3e012d4cfd1d9bf837870c961f462ca9f23ebe

Comments

Brian Norris Oct. 4, 2024, 11:24 p.m. UTC | #1 
On Tue, Sep 17, 2024 at 06:08:41PM +0300, Alper Nebi Yasak wrote:
> Replace one-element array with a flexible-array member in `struct
> mwifiex_ie_types_wildcard_ssid_params` to fix the following warning
> on a MT8173 Chromebook (mt8173-elm-hana):
> 
> [  356.775250] ------------[ cut here ]------------
> [  356.784543] memcpy: detected field-spanning write (size 6) of single field "wildcard_ssid_tlv->ssid" at drivers/net/wireless/marvell/mwifiex/scan.c:904 (size 1)
> [  356.813403] WARNING: CPU: 3 PID: 742 at drivers/net/wireless/marvell/mwifiex/scan.c:904 mwifiex_scan_networks+0x4fc/0xf28 [mwifiex]
> 
> The "(size 6)" above is exactly the length of the SSID of the network
> this device was connected to. The source of the warning looks like:
> 
>     ssid_len = user_scan_in->ssid_list[i].ssid_len;
>     [...]
>     memcpy(wildcard_ssid_tlv->ssid,
>            user_scan_in->ssid_list[i].ssid, ssid_len);
> 
> Also adjust a #define that uses sizeof() on this struct to keep the
> value same as before.
> 
> Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
> ---
> I found these relevant patches that modify other such arrays, where the
> second one removes a -1 from some sizeof() calculation:
> 
> https://lore.kernel.org/lkml/Y9xkECG3uTZ6T1dN@work/T/#u
> https://lore.kernel.org/lkml/ZsZa5xRcsLq9D+RX@elsanto/T/#u
> 
> So I think we need the +1 to keep things same. But it appears to work
> fine without it, so I'm not sure. Maybe it should've had a -1 before
> that I would remove with this?

Thanks for the investigation and patch! I believe I agree with the other
comments, that then "+ 1" isn't necessary. It's just a wasteful extra
byte of allocation. Can you send a v2? (Bonus: with the suggested Fixes
tag. Double bonus if you test KASAN with __counted_by, for a second
patch.)

Thanks,
Brian
diff mbox series

Patch

diff --git a/drivers/net/wireless/marvell/mwifiex/fw.h b/drivers/net/wireless/marvell/mwifiex/fw.h
index d03129d5d24e..4a96281792cc 100644
--- a/drivers/net/wireless/marvell/mwifiex/fw.h
+++ b/drivers/net/wireless/marvell/mwifiex/fw.h
@@ -875,7 +875,7 @@  struct mwifiex_ietypes_chanstats {
 struct mwifiex_ie_types_wildcard_ssid_params {
 	struct mwifiex_ie_types_header header;
 	u8 max_ssid_length;
-	u8 ssid[1];
+	u8 ssid[];
 } __packed;
 
 #define TSF_DATA_SIZE            8
diff --git a/drivers/net/wireless/marvell/mwifiex/scan.c b/drivers/net/wireless/marvell/mwifiex/scan.c
index cab889af4c4a..50af78ee935b 100644
--- a/drivers/net/wireless/marvell/mwifiex/scan.c
+++ b/drivers/net/wireless/marvell/mwifiex/scan.c
@@ -32,7 +32,7 @@ 
 #define WILDCARD_SSID_TLV_MAX_SIZE  \
 	(MWIFIEX_MAX_SSID_LIST_LENGTH *					\
 		(sizeof(struct mwifiex_ie_types_wildcard_ssid_params)	\
-			+ IEEE80211_MAX_SSID_LEN))
+			+ IEEE80211_MAX_SSID_LEN + 1))
 
 /* Maximum memory needed for a mwifiex_scan_cmd_config with all TLVs at max */
 #define MAX_SCAN_CFG_ALLOC (sizeof(struct mwifiex_scan_cmd_config)        \