Subject: [PATCH] net/sun3_82586: Avoid reading past buffer in debug output

From: Kees Cook <[email-masked]>
Date: Tue, 6 Feb 2024 08:16:54 -0800

Since NUM_XMIT_BUFFS is always 1, building m68k with sun3_defconfig and
-Warraybounds, this build warning is visible[1]:

drivers/net/ethernet/i825xx/sun3_82586.c: In function 'sun3_82586_timeout':
drivers/net/ethernet/i825xx/sun3_82586.c:990:122: warning: array subscript 1 is above array bounds of 'volatile struct transmit_cmd_struct *[1]' [-Warray-bounds=]
  990 |                 printk("%s: command-stats: %04x %04x\n",dev->name,swab16(p->xmit_cmds[0]->cmd_status),swab16(p->xmit_cmds[1]->cmd_status));
      |                                                                                                               ~~~~~~~~~~~~^~~
...
drivers/net/ethernet/i825xx/sun3_82586.c:156:46: note: while referencing 'xmit_cmds'
  156 |         volatile struct transmit_cmd_struct *xmit_cmds[NUM_XMIT_BUFFS];

Avoid accessing index 1 since it doesn't exist.

Link: https://github.com/KSPP/linux/issues/325 [1]
Cc: Sam Creasey <[email-masked]>
Cc: "David S. Miller" <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Cc: Jakub Kicinski <[email-masked]>
Cc: Paolo Abeni <[email-masked]>
Cc: Gustavo A. R. Silva <[email-masked]>
Cc: [email-masked]
Signed-off-by: Kees Cook <[email-masked]>
---
 drivers/net/ethernet/i825xx/sun3_82586.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/i825xx/sun3_82586.c b/drivers/net/ethernet/i825xx/sun3_82586.c
index 5e27470c6b1e..f2d4669c81cf 100644
--- a/drivers/net/ethernet/i825xx/sun3_82586.c
+++ b/drivers/net/ethernet/i825xx/sun3_82586.c
@@ -987,7 +987,7 @@ static void sun3_82586_timeout(struct net_device *dev, unsigned int txqueue)
 	{
 #ifdef DEBUG
 		printk("%s: xmitter timed out, try to restart! stat: %02x\n",dev->name,p->scb->cus);
-		printk("%s: command-stats: %04x %04x\n",dev->name,swab16(p->xmit_cmds[0]->cmd_status),swab16(p->xmit_cmds[1]->cmd_status));
+		printk("%s: command-stats: %04x\n", dev->name, swab16(p->xmit_cmds[0]->cmd_status));
 		printk("%s: check, whether you set the right interrupt number!\n",dev->name);
 #endif
 		sun3_82586_close(dev);
-- 
2.34.1