[PATCH] Fix buffer overflow and races in capi debug functions

The CAPI trace debug functions were using a fixed size buffer, which can be
overflowed if wrong formatted CAPI messages were sent to the kernel capi
layer. The code was also not protected against multiple callers. This fix
bug 8028.

Additionally the patch make the CAPI trace functions optional.

Signed-off-by: Karsten Keil <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/isdn/capi/Kconfig

···
 # Config.in for the CAPI subsystem
 #
 config ISDN_DRV_AVMB1_VERBOSE_REASON
-	bool "Verbose reason code reporting (kernel size +=7K)"
+	bool "Verbose reason code reporting"
 	depends on ISDN_CAPI
+	default y
 	help
-	  If you say Y here, the AVM B1 driver will give verbose reasons for
+	  If you say Y here, the CAPI drivers will give verbose reasons for
 	  disconnecting. This will increase the size of the kernel by 7 KB. If
 	  unsure, say Y.
+
+config CAPI_TRACE
+	bool "CAPI trace support"
+	depends on ISDN_CAPI
+	default y
+	help
+	  If you say Y here, the kernelcapi driver can make verbose traces
+	  of CAPI messages. This feature can be enabled/disabled via IOCTL for
+	  every controler (default disabled).
+	  This will increase the size of the kernelcapi module by 20 KB.
+	  If unsure, say Y.
 
 config ISDN_CAPI_MIDDLEWARE
 	bool "CAPI2.0 Middleware support (EXPERIMENTAL)"

drivers/isdn/capi/capidrv.c

···
 	capidrv_contr *card = findcontrbynumber(cmsg->adr.adrController & 0x7f);
 	capidrv_plci *plcip;
 	isdn_ctrl cmd;
+	_cdebbuf *cdb;
 
 	if (!card) {
 		printk(KERN_ERR "capidrv: %s from unknown controller 0x%x\n",
···
 				break;
 			}
 		}
-		printk(KERN_ERR "capidrv-%d: %s\n",
-				card->contrnr, capi_cmsg2str(cmsg));
+		cdb = capi_cmsg2str(cmsg);
+		if (cdb) {
+			printk(KERN_WARNING "capidrv-%d: %s\n",
+				card->contrnr, cdb->buf);
+			cdebbuf_free(cdb);
+		} else
+			printk(KERN_WARNING "capidrv-%d: CAPI_INFO_IND InfoNumber %x not handled\n",
+				card->contrnr, cmsg->InfoNumber);
+
 		break;
 
 	case CAPI_CONNECT_ACTIVE_CONF:		/* plci */
···
 static void capidrv_recv_message(struct capi20_appl *ap, struct sk_buff *skb)
 {
 	capi_message2cmsg(&s_cmsg, skb->data);
-	if (debugmode > 3)
-		printk(KERN_DEBUG "capidrv_signal: applid=%d %s\n",
-		       ap->applid, capi_cmsg2str(&s_cmsg));
-	
+	if (debugmode > 3) {
+		_cdebbuf *cdb = capi_cmsg2str(&s_cmsg);
+
+		if (cdb) {
+			printk(KERN_DEBUG "%s: applid=%d %s\n", __FUNCTION__,
+				ap->applid, cdb->buf);
+			cdebbuf_free(cdb);
+		} else
+			printk(KERN_DEBUG "%s: applid=%d %s not traced\n",
+				__FUNCTION__, ap->applid,
+				capi_cmd2str(s_cmsg.Command, s_cmsg.Subcommand));
+	}
 	if (s_cmsg.Command == CAPI_DATA_B3
 	    && s_cmsg.Subcommand == CAPI_IND) {
 		handle_data(&s_cmsg, skb);

drivers/isdn/capi/capiutil.c

···
 
 
 /*-------------------------------------------------------*/
+
+#ifdef CONFIG_CAPI_TRACE
+
 /*-------------------------------------------------------*/
 
 static char *pnames[] =
···
 };
 
 
-static char buf[8192];
-static char *p = NULL;
 
 #include <stdarg.h>
 
 /*-------------------------------------------------------*/
-static void bufprint(char *fmt,...)
+static _cdebbuf *bufprint(_cdebbuf *cdb, char *fmt,...)
 {
 	va_list f;
+	size_t n,r;
+
+	if (!cdb)
+		return NULL;
 	va_start(f, fmt);
-	vsprintf(p, fmt, f);
+	r = cdb->size - cdb->pos;
+	n = vsnprintf(cdb->p, r, fmt, f);
 	va_end(f);
-	p += strlen(p);
+	if (n >= r) {
+		/* truncated, need bigger buffer */
+		size_t ns = 2 * cdb->size;
+		u_char *nb;
+
+		while ((ns - cdb->pos) <= n)
+			ns *= 2;
+		nb = kmalloc(ns, GFP_ATOMIC);
+		if (!nb) {
+			cdebbuf_free(cdb);
+			return NULL;
+		}
+		memcpy(nb, cdb->buf, cdb->pos);
+		kfree(cdb->buf);
+		nb[cdb->pos] = 0;
+		cdb->buf = nb;
+		cdb->p = cdb->buf + cdb->pos;
+		cdb->size = ns;
+		va_start(f, fmt);
+		r = cdb->size - cdb->pos;
+		n = vsnprintf(cdb->p, r, fmt, f);
+		va_end(f);
+	}
+	cdb->p += n;
+	cdb->pos += n;
+	return cdb;
 }
 
-static void printstructlen(u8 * m, unsigned len)
+static _cdebbuf *printstructlen(_cdebbuf *cdb, u8 * m, unsigned len)
 {
 	unsigned hex = 0;
+
+	if (!cdb)
+		return NULL;
 	for (; len; len--, m++)
 		if (isalnum(*m) || *m == ' ') {
 			if (hex)
-				bufprint(">");
-			bufprint("%c", *m);
+				cdb = bufprint(cdb, ">");
+			cdb = bufprint(cdb, "%c", *m);
 			hex = 0;
 		} else {
 			if (!hex)
-				bufprint("<%02x", *m);
+				cdb = bufprint(cdb, "<%02x", *m);
 			else
-				bufprint(" %02x", *m);
+				cdb = bufprint(cdb, " %02x", *m);
 			hex = 1;
 		}
 	if (hex)
-		bufprint(">");
+		cdb = bufprint(cdb, ">");
+	return cdb;
 }
 
-static void printstruct(u8 * m)
+static _cdebbuf *printstruct(_cdebbuf *cdb, u8 * m)
 {
 	unsigned len;
+
 	if (m[0] != 0xff) {
 		len = m[0];
 		m += 1;
···
 		len = ((u16 *) (m + 1))[0];
 		m += 3;
 	}
-	printstructlen(m, len);
+	cdb = printstructlen(cdb, m, len);
+	return cdb;
 }
 
 /*-------------------------------------------------------*/
 #define NAME (pnames[cmsg->par[cmsg->p]])
 
-static void protocol_message_2_pars(_cmsg * cmsg, int level)
+static _cdebbuf *protocol_message_2_pars(_cdebbuf *cdb, _cmsg *cmsg, int level)
 {
 	for (; TYP != _CEND; cmsg->p++) {
 		int slen = 29 + 3 - level;
 		int i;
 
-		bufprint("  ");
+		if (!cdb)
+			return NULL;
+		cdb = bufprint(cdb, "  ");
 		for (i = 0; i < level - 1; i++)
-			bufprint(" ");
+			cdb = bufprint(cdb, " ");
 
 		switch (TYP) {
 		case _CBYTE:
-			bufprint("%-*s = 0x%x\n", slen, NAME, *(u8 *) (cmsg->m + cmsg->l));
+			cdb = bufprint(cdb, "%-*s = 0x%x\n", slen, NAME, *(u8 *) (cmsg->m + cmsg->l));
 			cmsg->l++;
 			break;
 		case _CWORD:
-			bufprint("%-*s = 0x%x\n", slen, NAME, *(u16 *) (cmsg->m + cmsg->l));
+			cdb = bufprint(cdb, "%-*s = 0x%x\n", slen, NAME, *(u16 *) (cmsg->m + cmsg->l));
 			cmsg->l += 2;
 			break;
 		case _CDWORD:
-			bufprint("%-*s = 0x%lx\n", slen, NAME, *(u32 *) (cmsg->m + cmsg->l));
+			cdb = bufprint(cdb, "%-*s = 0x%lx\n", slen, NAME, *(u32 *) (cmsg->m + cmsg->l));
 			cmsg->l += 4;
 			break;
 		case _CSTRUCT:
-			bufprint("%-*s = ", slen, NAME);
+			cdb = bufprint(cdb, "%-*s = ", slen, NAME);
 			if (cmsg->m[cmsg->l] == '\0')
-				bufprint("default");
+				cdb = bufprint(cdb, "default");
 			else
-				printstruct(cmsg->m + cmsg->l);
-			bufprint("\n");
+				cdb = printstruct(cdb, cmsg->m + cmsg->l);
+			cdb = bufprint(cdb, "\n");
 			if (cmsg->m[cmsg->l] != 0xff)
 				cmsg->l += 1 + cmsg->m[cmsg->l];
 			else
···
 		case _CMSTRUCT:
 /*----- Metastruktur 0 -----*/
 			if (cmsg->m[cmsg->l] == '\0') {
-				bufprint("%-*s = default\n", slen, NAME);
+				cdb = bufprint(cdb, "%-*s = default\n", slen, NAME);
 				cmsg->l++;
 				jumpcstruct(cmsg);
 			} else {
 				char *name = NAME;
 				unsigned _l = cmsg->l;
-				bufprint("%-*s\n", slen, name);
+				cdb = bufprint(cdb, "%-*s\n", slen, name);
 				cmsg->l = (cmsg->m + _l)[0] == 255 ? cmsg->l + 3 : cmsg->l + 1;
 				cmsg->p++;
-				protocol_message_2_pars(cmsg, level + 1);
+				cdb = protocol_message_2_pars(cdb, cmsg, level + 1);
 			}
 			break;
 		}
 	}
+	return cdb;
 }
 /*-------------------------------------------------------*/
-char *capi_message2str(u8 * msg)
+
+static _cdebbuf *g_debbuf;
+static u_long g_debbuf_lock;
+static _cmsg *g_cmsg;
+
+_cdebbuf *cdebbuf_alloc(void)
 {
+	_cdebbuf *cdb;
 
-	_cmsg cmsg;
-	p = buf;
-	p[0] = 0;
+	if (likely(!test_and_set_bit(1, &g_debbuf_lock))) {
+		cdb = g_debbuf;
+		goto init;
+	} else
+		cdb = kmalloc(sizeof(_cdebbuf), GFP_ATOMIC);
+	if (!cdb)
+		return NULL;
+	cdb->buf = kmalloc(CDEBUG_SIZE, GFP_ATOMIC);
+	if (!cdb->buf) {
+		kfree(cdb);
+		return NULL;
+	}
+	cdb->size = CDEBUG_SIZE;
+init:
+	cdb->buf[0] = 0;
+	cdb->p = cdb->buf;
+	cdb->pos = 0;
+	return cdb;
+}
 
-	cmsg.m = msg;
-	cmsg.l = 8;
-	cmsg.p = 0;
-	byteTRcpy(cmsg.m + 4, &cmsg.Command);
-	byteTRcpy(cmsg.m + 5, &cmsg.Subcommand);
-	cmsg.par = cpars[command_2_index(cmsg.Command, cmsg.Subcommand)];
+void cdebbuf_free(_cdebbuf *cdb)
+{
+	if (likely(cdb == g_debbuf)) {
+		test_and_clear_bit(1, &g_debbuf_lock);
+		return;
+	}
+	if (likely(cdb))
+		kfree(cdb->buf);
+	kfree(cdb);
+}
 
-	bufprint("%-26s ID=%03d #0x%04x LEN=%04d\n",
-		 mnames[command_2_index(cmsg.Command, cmsg.Subcommand)],
+
+_cdebbuf *capi_message2str(u8 * msg)
+{
+	_cdebbuf *cdb;
+	_cmsg	*cmsg;
+
+	cdb = cdebbuf_alloc();
+	if (unlikely(!cdb))
+		return NULL;
+	if (likely(cdb == g_debbuf))
+		cmsg = g_cmsg;
+	else
+		cmsg = kmalloc(sizeof(_cmsg), GFP_ATOMIC);
+	if (unlikely(!cmsg)) {
+		cdebbuf_free(cdb);
+		return NULL;
+	}
+	cmsg->m = msg;
+	cmsg->l = 8;
+	cmsg->p = 0;
+	byteTRcpy(cmsg->m + 4, &cmsg->Command);
+	byteTRcpy(cmsg->m + 5, &cmsg->Subcommand);
+	cmsg->par = cpars[command_2_index(cmsg->Command, cmsg->Subcommand)];
+
+	cdb = bufprint(cdb, "%-26s ID=%03d #0x%04x LEN=%04d\n",
+		 mnames[command_2_index(cmsg->Command, cmsg->Subcommand)],
 		 ((unsigned short *) msg)[1],
 		 ((unsigned short *) msg)[3],
 		 ((unsigned short *) msg)[0]);
 
-	protocol_message_2_pars(&cmsg, 1);
-	return buf;
+	cdb = protocol_message_2_pars(cdb, cmsg, 1);
+	if (unlikely(cmsg != g_cmsg))
+		kfree(cmsg);
+	return cdb;
 }
 
-char *capi_cmsg2str(_cmsg * cmsg)
+_cdebbuf *capi_cmsg2str(_cmsg * cmsg)
 {
-	p = buf;
-	p[0] = 0;
+	_cdebbuf *cdb;
+
+	cdb = cdebbuf_alloc();
+	if (!cdb)
+		return NULL;
 	cmsg->l = 8;
 	cmsg->p = 0;
-	bufprint("%s ID=%03d #0x%04x LEN=%04d\n",
+	cdb = bufprint(cdb, "%s ID=%03d #0x%04x LEN=%04d\n",
 		 mnames[command_2_index(cmsg->Command, cmsg->Subcommand)],
 		 ((u16 *) cmsg->m)[1],
 		 ((u16 *) cmsg->m)[3],
 		 ((u16 *) cmsg->m)[0]);
-	protocol_message_2_pars(cmsg, 1);
-	return buf;
+	cdb = protocol_message_2_pars(cdb, cmsg, 1);
+	return cdb;
 }
 
+int __init cdebug_init(void)
+{
+	g_cmsg= kmalloc(sizeof(_cmsg), GFP_KERNEL);
+	if (!g_cmsg)
+		return ENOMEM;
+	g_debbuf = kmalloc(sizeof(_cdebbuf), GFP_KERNEL);
+	if (!g_debbuf) {
+		kfree(g_cmsg);
+		return ENOMEM;
+	}
+	g_debbuf->buf = kmalloc(CDEBUG_GSIZE, GFP_KERNEL);
+	if (!g_debbuf->buf) {
+		kfree(g_cmsg);
+		kfree(g_debbuf);
+		return ENOMEM;;
+	}
+	g_debbuf->size = CDEBUG_GSIZE;
+	g_debbuf->buf[0] = 0;
+	g_debbuf->p = g_debbuf->buf;
+	g_debbuf->pos = 0;
+	return 0;
+}
+
+void __exit cdebug_exit(void)
+{
+	if (g_debbuf)
+		kfree(g_debbuf->buf);
+	kfree(g_debbuf);
+	kfree(g_cmsg);
+}
+
+#else /* !CONFIG_CAPI_TRACE */
+
+static _cdebbuf g_debbuf = {"CONFIG_CAPI_TRACE not enabled", NULL, 0, 0};
+
+_cdebbuf *capi_message2str(u8 * msg)
+{
+	return &g_debbuf;
+}
+
+_cdebbuf *capi_cmsg2str(_cmsg * cmsg)
+{
+	return &g_debbuf;
+}
+
+_cdebbuf *cdebbuf_alloc(void)
+{
+	return &g_debbuf;
+}
+
+void cdebbuf_free(_cdebbuf *cdb)
+{
+}
+
+int __init cdebug_init(void)
+{
+	return 0;
+}
+
+void __exit cdebug_exit(void)
+{
+}
+
+#endif
+
+EXPORT_SYMBOL(cdebbuf_alloc);
+EXPORT_SYMBOL(cdebbuf_free);
 EXPORT_SYMBOL(capi_cmsg2message);
 EXPORT_SYMBOL(capi_message2cmsg);
 EXPORT_SYMBOL(capi_cmsg_header);

drivers/isdn/capi/kcapi.c

···
 	int showctl = 0;
 	u8 cmd, subcmd;
 	unsigned long flags;
+	_cdebbuf *cdb;
 
 	if (card->cardstate != CARD_RUNNING) {
-		printk(KERN_INFO "kcapi: controller %d not active, got: %s",
-		       card->cnr, capi_message2str(skb->data));
+		cdb = capi_message2str(skb->data);
+		if (cdb) {
+			printk(KERN_INFO "kcapi: controller [%03d] not active, got: %s",
+				card->cnr, cdb->buf);
+			cdebbuf_free(cdb);
+		} else
+			printk(KERN_INFO "kcapi: controller [%03d] not active, cannot trace\n",
+				card->cnr);
 		goto error;
 	}
 
···
 	showctl |= (card->traceflag & 1);
 	if (showctl & 2) {
 		if (showctl & 1) {
-			printk(KERN_DEBUG "kcapi: got [0x%lx] id#%d %s len=%u\n",
-			       (unsigned long) card->cnr,
-			       CAPIMSG_APPID(skb->data),
+			printk(KERN_DEBUG "kcapi: got [%03d] id#%d %s len=%u\n",
+			       card->cnr, CAPIMSG_APPID(skb->data),
 			       capi_cmd2str(cmd, subcmd),
 			       CAPIMSG_LEN(skb->data));
 		} else {
-			printk(KERN_DEBUG "kcapi: got [0x%lx] %s\n",
-					(unsigned long) card->cnr,
-					capi_message2str(skb->data));
+			cdb = capi_message2str(skb->data);
+			if (cdb) {
+				printk(KERN_DEBUG "kcapi: got [%03d] %s\n",
+					card->cnr, cdb->buf);
+				cdebbuf_free(cdb);
+			} else
+				printk(KERN_DEBUG "kcapi: got [%03d] id#%d %s len=%u, cannot trace\n",
+					card->cnr, CAPIMSG_APPID(skb->data),
+					capi_cmd2str(cmd, subcmd),
+					CAPIMSG_LEN(skb->data));
 		}
 
 	}
···
 	ap = get_capi_appl_by_nr(CAPIMSG_APPID(skb->data));
 	if ((!ap) || (ap->release_in_progress)) {
 		read_unlock_irqrestore(&application_lock, flags);
-		printk(KERN_ERR "kcapi: handle_message: applid %d state released (%s)\n",
-			CAPIMSG_APPID(skb->data), capi_message2str(skb->data));
+		cdb = capi_message2str(skb->data);
+		if (cdb) {
+			printk(KERN_ERR "kcapi: handle_message: applid %d state released (%s)\n",
+			CAPIMSG_APPID(skb->data), cdb->buf);
+			cdebbuf_free(cdb);
+		} else
+			printk(KERN_ERR "kcapi: handle_message: applid %d state released (%s) cannot trace\n",
+				CAPIMSG_APPID(skb->data),
+				capi_cmd2str(cmd, subcmd));
 		goto error;
 	}
 	skb_queue_tail(&ap->recv_queue, skb);
···
 {
 	card->cardstate = CARD_RUNNING;
 
-        printk(KERN_NOTICE "kcapi: card %d \"%s\" ready.\n",
+        printk(KERN_NOTICE "kcapi: card [%03d] \"%s\" ready.\n",
 	       card->cnr, card->name);
 
 	notify_push(KCI_CONTRUP, card->cnr, 0, 0);
···
 		capi_ctr_put(card);
 	}
 
-	printk(KERN_NOTICE "kcapi: card %d down.\n", card->cnr);
+	printk(KERN_NOTICE "kcapi: card [%03d] down.\n", card->cnr);
 
 	notify_push(KCI_CONTRDOWN, card->cnr, 0, 0);
 }
···
 void capi_ctr_suspend_output(struct capi_ctr *card)
 {
 	if (!card->blocked) {
-		printk(KERN_DEBUG "kcapi: card %d suspend\n", card->cnr);
+		printk(KERN_DEBUG "kcapi: card [%03d] suspend\n", card->cnr);
 		card->blocked = 1;
 	}
 }
···
 void capi_ctr_resume_output(struct capi_ctr *card)
 {
 	if (card->blocked) {
-		printk(KERN_DEBUG "kcapi: card %d resume\n", card->cnr);
+		printk(KERN_DEBUG "kcapi: card [%03d] resume\n", card->cnr);
 		card->blocked = 0;
 	}
 }
···
 	}
 
 	ncards++;
-	printk(KERN_NOTICE "kcapi: Controller %d: %s attached\n",
+	printk(KERN_NOTICE "kcapi: Controller [%03d]: %s attached\n",
 			card->cnr, card->name);
 	return 0;
 }
···
 	   card->procent = NULL;
 	}
 	capi_cards[card->cnr - 1] = NULL;
-	printk(KERN_NOTICE "kcapi: Controller %d: %s unregistered\n",
+	printk(KERN_NOTICE "kcapi: Controller [%03d]: %s unregistered\n",
 			card->cnr, card->name);
 
 	return 0;
···
 	showctl |= (card->traceflag & 1);
 	if (showctl & 2) {
 		if (showctl & 1) {
-			printk(KERN_DEBUG "kcapi: put [%#x] id#%d %s len=%u\n",
+			printk(KERN_DEBUG "kcapi: put [%03d] id#%d %s len=%u\n",
 			       CAPIMSG_CONTROLLER(skb->data),
 			       CAPIMSG_APPID(skb->data),
 			       capi_cmd2str(cmd, subcmd),
 			       CAPIMSG_LEN(skb->data));
 		} else {
-			printk(KERN_DEBUG "kcapi: put [%#x] %s\n",
-			       CAPIMSG_CONTROLLER(skb->data),
-			       capi_message2str(skb->data));
+			_cdebbuf *cdb = capi_message2str(skb->data);
+			if (cdb) {
+				printk(KERN_DEBUG "kcapi: put [%03d] %s\n",
+					CAPIMSG_CONTROLLER(skb->data),
+					cdb->buf);
+				cdebbuf_free(cdb);
+			} else
+				printk(KERN_DEBUG "kcapi: put [%03d] id#%d %s len=%u cannot trace\n",
+					CAPIMSG_CONTROLLER(skb->data),
+					CAPIMSG_APPID(skb->data),
+					capi_cmd2str(cmd, subcmd),
+					CAPIMSG_LEN(skb->data));
 		}
-
 	}
 	return card->send_message(card, skb);
 }
···
 			return -ESRCH;
 
 		card->traceflag = fdef.flag;
-		printk(KERN_INFO "kcapi: contr %d set trace=%d\n",
+		printk(KERN_INFO "kcapi: contr [%03d] set trace=%d\n",
 			card->cnr, card->traceflag);
 		return 0;
 	}
···
 {
 	char *p;
 	char rev[32];
+	int ret;
 
+	ret = cdebug_init();
+	if (ret)
+		return ret;
         kcapi_proc_init();
 
 	if ((p = strchr(revision, ':')) != 0 && p[1]) {
···
 
 	/* make sure all notifiers are finished */
 	flush_scheduled_work();
+	cdebug_exit();
 }
 
 module_init(kcapi_init);

include/linux/isdn/capiutil.h

···
 /*
  * Debugging / Tracing functions
  */
+
 char *capi_cmd2str(__u8 cmd, __u8 subcmd);
-char *capi_cmsg2str(_cmsg * cmsg);
-char *capi_message2str(__u8 * msg);
+
+typedef struct {
+	u_char	*buf;
+	u_char	*p;
+	size_t	size;
+	size_t	pos;
+} _cdebbuf;
+
+#define	CDEBUG_SIZE	1024
+#define	CDEBUG_GSIZE	4096
+
+_cdebbuf *cdebbuf_alloc(void);
+void cdebbuf_free(_cdebbuf *cdb);
+int cdebug_init(void);
+void cdebug_exit(void);
+
+_cdebbuf *capi_cmsg2str(_cmsg *cmsg);
+_cdebbuf *capi_message2str(__u8 *msg);
 
 /*-----------------------------------------------------------------------*/