unaligned access by multipathd logging

unaligned access by multipathd logging

[Jun'ichi Nomura]

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Hi,

Logging code in multipathd cause unaligned access
which, on ia64, yields logs on both console and syslog like:
unaligned access to 0x60000000000141d1, ip=0x4000000000009d81

It's harmless except for the slight performance effect.
However, it's annoying for users and better to fix.

Attached patch aligns the la->tail to pointer size.
Patch is created on multipath-tools 0.4.4.
Please consider to apply.

This is a gdb trace of the case, for your reference:
#0  log_enqueue (prio=5, fmt=0x4000000000045970 "read /etc/multipath.conf",
    ap=0x6000000000013f70) at log.c:130
130             msg->prio = prio;
(gdb) where
#0  log_enqueue (prio=5, fmt=0x4000000000045970 "read /etc/multipath.conf",
    ap=0x6000000000013f70) at log.c:130
#1  0x400000000000a390 in log_safe (prio=5,
    fmt=0x4000000000045970 "read /etc/multipath.conf") at log_pthread.c:16
#2  0x4000000000007f60 in child (param=0x0) at main.c:883
#3  0x2000000000275930 in __clone2 () from /lib/tls/libc.so.6.1
(gdb) p msg
$1 = (struct logmsg *) 0x60000000000141d1
(gdb) p la->tail
$2 = (void *) 0x60000000000141d1
(gdb) p/x fwd
$3 = 0x31

Thanks,
Jun'ichi Nomura

[-- Attachment #2: logarea.patch --]
[-- Type: text/x-patch, Size: 1082 bytes --]

--- multipath-tools-0.4.4/multipathd/log.c.orig	2005-05-04 16:46:14.146824760 -0400
+++ multipath-tools-0.4.4/multipathd/log.c	2005-05-04 17:08:39.212237970 -0400
@@ -89,6 +89,7 @@ void log_close (void)
 	return;
 }
 
+#define ALIGN(len, s) (((len)+(s)-1)/(s)*(s))
 int log_enqueue (int prio, const char * fmt, va_list ap)
 {
 	int len, fwd;
@@ -101,10 +102,10 @@ int log_enqueue (int prio, const char * 
 	if (!la->empty) {
 		fwd = sizeof(struct logmsg) + 
 		      strlen((char *)&lastmsg->str) * sizeof(char) + 1;
-		la->tail += fwd;
+		la->tail += ALIGN(fwd, sizeof(void *));
 	}
 	vsnprintf(buff, MAX_MSG_SIZE, fmt, ap);
-	len = strlen(buff) * sizeof(char) + 1;
+	len = ALIGN(strlen(buff) * sizeof(char) + 1, sizeof(void *));
 
 	/* not enough space on tail : rewind */
 	if (la->head <= la->tail &&
@@ -128,7 +129,7 @@ int log_enqueue (int prio, const char * 
 	la->empty = 0;
 	msg = (struct logmsg *)la->tail;
 	msg->prio = prio;
-	memcpy((void *)&msg->str, buff, len);
+	memcpy((void *)&msg->str, buff, strlen(buff));
 	lastmsg->next = la->tail;
 	msg->next = la->head;
 

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Re: unaligned access by multipathd logging

[christophe varoqui]

Nice piece of brain work, thanks.

I applied this patch, and it will appear as commit
544bfcea0e63d32d4cf79abb97b6e78918fb5511 on kernel.org git repository.

Regards,
cvaroqui

On jeu, 2005-05-05 at 17:42 -0400, Jun'ichi Nomura wrote:
> Hi,
> 
> Logging code in multipathd cause unaligned access
> which, on ia64, yields logs on both console and syslog like:
> unaligned access to 0x60000000000141d1, ip=0x4000000000009d81
> 
> It's harmless except for the slight performance effect.
> However, it's annoying for users and better to fix.
> 
> Attached patch aligns the la->tail to pointer size.
> Patch is created on multipath-tools 0.4.4.
> Please consider to apply.
>