[PATCH v2 1/3] wifi: mwifiex: Fix tlv_buf_left calculation
From: Gustavo A. R. Silva
Date: Thu Aug 24 2023 - 23:06:33 EST
In a TLV encoding scheme, the Length part represents the length after
the header containing the values for type and length. In this case,
`tlv_len` should be:
tlv_len == (sizeof(*tlv_rxba) - 1) - sizeof(tlv_rxba->header) + tlv_bitmap_len
Notice that the `- 1` accounts for the one-element array `bitmap`, which
1-byte size is already included in `sizeof(*tlv_rxba)`.
So, if the above is correct, there is a double-counting of some members
in `struct mwifiex_ie_types_rxba_sync`, when `tlv_buf_left` and `tmp`
are calculated:
968 tlv_buf_left -= (sizeof(*tlv_rxba) + tlv_len);
969 tmp = (u8 *)tlv_rxba + tlv_len + sizeof(*tlv_rxba);
in specific, members:
drivers/net/wireless/marvell/mwifiex/fw.h:777
777 u8 mac[ETH_ALEN];
778 u8 tid;
779 u8 reserved;
780 __le16 seq_num;
781 __le16 bitmap_len;
This is clearly wrong, and affects the subsequent decoding of data in
`event_buf` through `tlv_rxba`:
970 tlv_rxba = (struct mwifiex_ie_types_rxba_sync *)tmp;
Fix this by using `sizeof(tlv_rxba->header)` instead of `sizeof(*tlv_rxba)`
in the calculation of `tlv_buf_left` and `tmp`.
This results in the following binary differences before/after changes:
| drivers/net/wireless/marvell/mwifiex/11n_rxreorder.o
| @@ -4698,11 +4698,11 @@
| drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c:968
| tlv_buf_left -= (sizeof(tlv_rxba->header) + tlv_len);
| - 1da7: lea -0x11(%rbx),%edx
| + 1da7: lea -0x4(%rbx),%edx
| 1daa: movzwl %bp,%eax
| drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c:969
| tmp = (u8 *)tlv_rxba + sizeof(tlv_rxba->header) + tlv_len;
| - 1dad: lea 0x11(%r15,%rbp,1),%r15
| + 1dad: lea 0x4(%r15,%rbp,1),%r15
The above reflects the desired change: avoid counting 13 too many bytes;
which is the total size of the double-counted members in
`struct mwifiex_ie_types_rxba_sync`:
$ pahole -C mwifiex_ie_types_rxba_sync drivers/net/wireless/marvell/mwifiex/11n_rxreorder.o
struct mwifiex_ie_types_rxba_sync {
struct mwifiex_ie_types_header header; /* 0 4 */
|-----------------------------------------------------------------------
| u8 mac[6]; /* 4 6 */ |
| u8 tid; /* 10 1 */ |
| u8 reserved; /* 11 1 */ |
| __le16 seq_num; /* 12 2 */ |
| __le16 bitmap_len; /* 14 2 */ |
| u8 bitmap[1]; /* 16 1 */ |
|----------------------------------------------------------------------|
| 13 bytes|
-----------
/* size: 17, cachelines: 1, members: 7 */
/* last cacheline: 17 bytes */
} __attribute__((__packed__));
Fixes: 99ffe72cdae4 ("mwifiex: process rxba_sync event")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
---
Changes in v2:
- Fix typo in changelog text: s/too bytes/too many bytes
- Update binary diff snapshot in changelog text.
v1:
- Link: https://lore.kernel.org/linux-hardening/698dc480d939e3ae490140db5c2f36eb84093594.1692829410.git.gustavoars@xxxxxxxxxx/
drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
index 391793a16adc..d1d3632a3ed7 100644
--- a/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
+++ b/drivers/net/wireless/marvell/mwifiex/11n_rxreorder.c
@@ -965,8 +965,8 @@ void mwifiex_11n_rxba_sync_event(struct mwifiex_private *priv,
}
}
- tlv_buf_left -= (sizeof(*tlv_rxba) + tlv_len);
- tmp = (u8 *)tlv_rxba + tlv_len + sizeof(*tlv_rxba);
+ tlv_buf_left -= (sizeof(tlv_rxba->header) + tlv_len);
+ tmp = (u8 *)tlv_rxba + sizeof(tlv_rxba->header) + tlv_len;
tlv_rxba = (struct mwifiex_ie_types_rxba_sync *)tmp;
}
}
--
2.34.1