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Subject[PATCH] ath6kl: Use struct_group() to avoid size-mismatched casting
Date
In builds with -Warray-bounds, casts from smaller objects to larger
objects will produce warnings. These can be overly conservative, but since
-Warray-bounds has been finding legitimate bugs, it is desirable to turn
it on globally. Instead of casting a u32 to a larger object, redefine
the u32 portion of the header to a separate struct that can be used for
both u32 operations and the distinct header fields. Silences this warning:

drivers/net/wireless/ath/ath6kl/htc_mbox.c: In function 'htc_wait_for_ctrl_msg':
drivers/net/wireless/ath/ath6kl/htc_mbox.c:2275:20: error: array subscript 'struct htc_frame_hdr[0]' is partly outside array bounds of 'u32[1]' {aka 'unsigned int[1]'} [-Werror=array-bounds]
2275 | if (htc_hdr->eid != ENDPOINT_0)
| ^~
drivers/net/wireless/ath/ath6kl/htc_mbox.c:2264:13: note: while referencing 'look_ahead'
2264 | u32 look_ahead;
| ^~~~~~~~~~

This change results in no executable instruction differences.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/net/wireless/ath/ath6kl/htc.h | 19 +++++++++++++------
drivers/net/wireless/ath/ath6kl/htc_mbox.c | 15 ++++++---------
2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/net/wireless/ath/ath6kl/htc.h b/drivers/net/wireless/ath/ath6kl/htc.h
index 112d8a9b8d43..d3534a29c4f0 100644
--- a/drivers/net/wireless/ath/ath6kl/htc.h
+++ b/drivers/net/wireless/ath/ath6kl/htc.h
@@ -153,12 +153,19 @@
* implementations.
*/
struct htc_frame_hdr {
- u8 eid;
- u8 flags;
-
- /* length of data (including trailer) that follows the header */
- __le16 payld_len;
-
+ struct_group_tagged(htc_frame_look_ahead, header,
+ union {
+ struct {
+ u8 eid;
+ u8 flags;
+
+ /* length of data (including trailer) that follows the header */
+ __le16 payld_len;
+
+ };
+ u32 word;
+ };
+ );
/* end of 4-byte lookahead */

u8 ctrl[2];
diff --git a/drivers/net/wireless/ath/ath6kl/htc_mbox.c b/drivers/net/wireless/ath/ath6kl/htc_mbox.c
index 998947ef63b6..e3874421c4c0 100644
--- a/drivers/net/wireless/ath/ath6kl/htc_mbox.c
+++ b/drivers/net/wireless/ath/ath6kl/htc_mbox.c
@@ -2260,19 +2260,16 @@ int ath6kl_htc_rxmsg_pending_handler(struct htc_target *target,
static struct htc_packet *htc_wait_for_ctrl_msg(struct htc_target *target)
{
struct htc_packet *packet = NULL;
- struct htc_frame_hdr *htc_hdr;
- u32 look_ahead;
+ struct htc_frame_look_ahead look_ahead;

- if (ath6kl_hif_poll_mboxmsg_rx(target->dev, &look_ahead,
+ if (ath6kl_hif_poll_mboxmsg_rx(target->dev, &look_ahead.word,
HTC_TARGET_RESPONSE_TIMEOUT))
return NULL;

ath6kl_dbg(ATH6KL_DBG_HTC,
- "htc rx wait ctrl look_ahead 0x%X\n", look_ahead);
-
- htc_hdr = (struct htc_frame_hdr *)&look_ahead;
+ "htc rx wait ctrl look_ahead 0x%X\n", look_ahead.word);

- if (htc_hdr->eid != ENDPOINT_0)
+ if (look_ahead.eid != ENDPOINT_0)
return NULL;

packet = htc_get_control_buf(target, false);
@@ -2281,8 +2278,8 @@ static struct htc_packet *htc_wait_for_ctrl_msg(struct htc_target *target)
return NULL;

packet->info.rx.rx_flags = 0;
- packet->info.rx.exp_hdr = look_ahead;
- packet->act_len = le16_to_cpu(htc_hdr->payld_len) + HTC_HDR_LENGTH;
+ packet->info.rx.exp_hdr = look_ahead.word;
+ packet->act_len = le16_to_cpu(look_ahead.payld_len) + HTC_HDR_LENGTH;

if (packet->act_len > packet->buf_len)
goto fail_ctrl_rx;
--
2.30.2
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