[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 <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 318 insertions, 78 deletions

diff --git a/drivers/isdn/capi/Kconfig b/drivers/isdn/capi/Kconfig
index 8b6c9a431ffa..c921d6c522f5 100644
--- a/drivers/isdn/capi/Kconfig
+++ b/drivers/isdn/capi/Kconfig
@@ -2,13 +2,25 @@
 # 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)"
         depends on ISDN_CAPI && EXPERIMENTAL
diff --git a/drivers/isdn/capi/capidrv.c b/drivers/isdn/capi/capidrv.c
index 2a49cea0a223..23b6f7bc16b7 100644
--- a/drivers/isdn/capi/capidrv.c
+++ b/drivers/isdn/capi/capidrv.c
@@ -990,6 +990,7 @@ static void handle_plci(_cmsg * cmsg)
         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",
@@ -1122,8 +1123,15 @@ static void handle_plci(_cmsg * cmsg)
                                 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 */
@@ -1371,10 +1379,18 @@ static _cmsg s_cmsg;
 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);
diff --git a/drivers/isdn/capi/capiutil.c b/drivers/isdn/capi/capiutil.c
index c1b21552fc03..ad1e2702c2d1 100644
--- a/drivers/isdn/capi/capiutil.c
+++ b/drivers/isdn/capi/capiutil.c
@@ -648,6 +648,9 @@ char *capi_cmd2str(u8 cmd, u8 subcmd)
 
 
 /*-------------------------------------------------------*/
+
+#ifdef CONFIG_CAPI_TRACE
+
 /*-------------------------------------------------------*/
 
 static char *pnames[] =
@@ -703,44 +706,77 @@ 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;
@@ -748,42 +784,45 @@ static void printstruct(u8 * m)
                 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
@@ -794,61 +833,184 @@ static void protocol_message_2_pars(_cmsg * cmsg, int level)
                 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;
+
+        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 cmsg;
-        p = buf;
-        p[0] = 0;
+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);
+}
 
-        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)];
 
-        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);
diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c
index 783a25526315..3ed34f7a1c4f 100644
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -276,10 +276,17 @@ void capi_ctr_handle_message(struct capi_ctr * card, u16 appl, struct sk_buff *s
         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;
         }
 
@@ -295,15 +302,21 @@ void capi_ctr_handle_message(struct capi_ctr * card, u16 appl, struct sk_buff *s
         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));
                 }
 
         }
@@ -312,8 +325,15 @@ void capi_ctr_handle_message(struct capi_ctr * card, u16 appl, struct sk_buff *s
         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);
@@ -332,7 +352,7 @@ void capi_ctr_ready(struct capi_ctr * card)
 {
         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);
@@ -364,7 +384,7 @@ void capi_ctr_reseted(struct capi_ctr * card)
                 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);
 }
@@ -374,7 +394,7 @@ EXPORT_SYMBOL(capi_ctr_reseted);
 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;
         }
 }
@@ -384,7 +404,7 @@ EXPORT_SYMBOL(capi_ctr_suspend_output);
 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;
         }
 }
@@ -432,7 +452,7 @@ attach_capi_ctr(struct capi_ctr *card)
         }
 
         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;
 }
@@ -451,7 +471,7 @@ int detach_capi_ctr(struct capi_ctr *card)
            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;
@@ -623,17 +643,25 @@ u16 capi20_put_message(struct capi20_appl *ap, struct sk_buff *skb)
         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);
 }
@@ -894,7 +922,7 @@ int capi20_manufacturer(unsigned int cmd, void __user *data)
                         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;
         }
@@ -967,7 +995,11 @@ static int __init kcapi_init(void)
 {
         char *p;
         char rev[32];
+        int ret;
 
+        ret = cdebug_init();
+        if (ret)
+                return ret;
         kcapi_proc_init();
 
         if ((p = strchr(revision, ':')) != 0 && p[1]) {
@@ -988,6 +1020,7 @@ static void __exit kcapi_exit(void)
 
         /* make sure all notifiers are finished */
         flush_scheduled_work();
+        cdebug_exit();
 }
 
 module_init(kcapi_init);
diff --git a/include/linux/isdn/capiutil.h b/include/linux/isdn/capiutil.h
index 2e79f816703b..63bd9cf821a7 100644
--- a/include/linux/isdn/capiutil.h
+++ b/include/linux/isdn/capiutil.h
@@ -174,9 +174,26 @@ char *capi_info2str(__u16 reason);
 /*
  * 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);
 
 /*-----------------------------------------------------------------------*/