[PATCH] wifi: iwlegacy: Fix "field-spanning write" warning in il_enqueue_hcmd()

[Ben Hutchings <ben@xxxxxxxxxxxxxxx>]

iwlegacy uses command buffers with a payload size of 320
bytes (default) or 4092 bytes (huge).  The struct il_device_cmd type
describes the default buffers and there is no separate type describing
the huge buffers.

The il_enqueue_hcmd() function works with both default and huge
buffers, and has a memcpy() to the buffer payload.  The size of
this copy may exceed 320 bytes when using a huge buffer, which
now results in a run-time warning:

    memcpy: detected field-spanning write (size 1014) of single field "&out_cmd->cmd.payload" at drivers/net/wireless/intel/iwlegacy/common.c:3170 (size 320)

To fix this:

- Define a new struct type for huge buffers, with a correctly sized
  payload field
- When using a huge buffer in il_enqueue_hcmd(), cast the command
  buffer pointer to that type when looking up the payload field

Reported-by: Martin-Éric Racine <martin-eric.racine@xxxxxx>
References: https://bugs.debian.org/1062421
References: https://bugzilla.kernel.org/show_bug.cgi?id=219124
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Fixes: 54d9469bc515 ("fortify: Add run-time WARN for cross-field memcpy()")
Tested-by: Martin-Éric Racine <martin-eric.racine@xxxxxx>
Tested-by: Brandon Nielsen <nielsenb@xxxxxxxxxxx>
---
 drivers/net/wireless/intel/iwlegacy/common.c | 13 ++++++++++++-
 drivers/net/wireless/intel/iwlegacy/common.h | 12 ++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlegacy/common.c b/drivers/net/wireless/intel/iwlegacy/common.c
index 9d33a66a49b5..4616293ec0cf 100644
--- a/drivers/net/wireless/intel/iwlegacy/common.c
+++ b/drivers/net/wireless/intel/iwlegacy/common.c
@@ -3122,6 +3122,7 @@ il_enqueue_hcmd(struct il_priv *il, struct il_host_cmd *cmd)
 	struct il_cmd_meta *out_meta;
 	dma_addr_t phys_addr;
 	unsigned long flags;
+	u8 *out_payload;
 	u32 idx;
 	u16 fix_size;
 
@@ -3157,6 +3158,16 @@ il_enqueue_hcmd(struct il_priv *il, struct il_host_cmd *cmd)
 	out_cmd = txq->cmd[idx];
 	out_meta = &txq->meta[idx];
 
+	/* The payload is in the same place in regular and huge
+	 * command buffers, but we need to let the compiler know when
+	 * we're using a larger payload buffer to avoid "field-
+	 * spanning write" warnings at run-time for huge commands.
+	 */
+	if (cmd->flags & CMD_SIZE_HUGE)
+		out_payload = ((struct il_device_cmd_huge *)out_cmd)->cmd.payload;
+	else
+		out_payload = out_cmd->cmd.payload;
+
 	if (WARN_ON(out_meta->flags & CMD_MAPPED)) {
 		spin_unlock_irqrestore(&il->hcmd_lock, flags);
 		return -ENOSPC;
@@ -3170,7 +3181,7 @@ il_enqueue_hcmd(struct il_priv *il, struct il_host_cmd *cmd)
 		out_meta->callback = cmd->callback;
 
 	out_cmd->hdr.cmd = cmd->id;
-	memcpy(&out_cmd->cmd.payload, cmd->data, cmd->len);
+	memcpy(out_payload, cmd->data, cmd->len);
 
 	/* At this point, the out_cmd now has all of the incoming cmd
 	 * information */
diff --git a/drivers/net/wireless/intel/iwlegacy/common.h b/drivers/net/wireless/intel/iwlegacy/common.h
index 69687fcf963f..027dae5619a3 100644
--- a/drivers/net/wireless/intel/iwlegacy/common.h
+++ b/drivers/net/wireless/intel/iwlegacy/common.h
@@ -560,6 +560,18 @@ struct il_device_cmd {
 
 #define TFD_MAX_PAYLOAD_SIZE (sizeof(struct il_device_cmd))
 
+/**
+ * struct il_device_cmd_huge
+ *
+ * For use when sending huge commands.
+ */
+struct il_device_cmd_huge {
+	struct il_cmd_header hdr;	/* uCode API */
+	union {
+		u8 payload[IL_MAX_CMD_SIZE - sizeof(struct il_cmd_header)];
+	} __packed cmd;
+} __packed;
+
 struct il_host_cmd {
 	const void *data;
 	unsigned long reply_page;

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