isdn/capi: prevent NULL pointer dereference on invalid CAPI command

An invalid CAPI 2.0 command/subcommand combination may retrieve a
NULL pointer from the cpars[] array which will later be dereferenced
by the parser routines.
Fix by adding NULL pointer checks in strategic places.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/isdn/capi/capiutil.c b/drivers/isdn/capi/capiutil.c
index 8e401eda2aa1..36835ef3f340 100644
--- a/drivers/isdn/capi/capiutil.c
+++ b/drivers/isdn/capi/capiutil.c
@@ -318,6 +318,8 @@ unsigned capi_cmsg2message(_cmsg *cmsg, u8 *msg)
         cmsg->l = 8;
         cmsg->p = 0;
         cmsg->par = capi_cmd2par(cmsg->Command, cmsg->Subcommand);
+        if (!cmsg->par)
+                return 1;       /* invalid command/subcommand */
 
         pars_2_message(cmsg);
 
@@ -391,6 +393,8 @@ unsigned capi_message2cmsg(_cmsg *cmsg, u8 *msg)
         byteTRcpy(cmsg->m + 4, &cmsg->Command);
         byteTRcpy(cmsg->m + 5, &cmsg->Subcommand);
         cmsg->par = capi_cmd2par(cmsg->Command, cmsg->Subcommand);
+        if (!cmsg->par)
+                return 1;       /* invalid command/subcommand */
 
         message_2_pars(cmsg);
 
@@ -640,6 +644,9 @@ static _cdebbuf *printstruct(_cdebbuf *cdb, u8 *m)
 
 static _cdebbuf *protocol_message_2_pars(_cdebbuf *cdb, _cmsg *cmsg, int level)
 {
+        if (!cmsg->par)
+                return NULL;    /* invalid command/subcommand */
+
         for (; TYP != _CEND; cmsg->p++) {
                 int slen = 29 + 3 - level;
                 int i;