isdn/kcapi: fix a small underflow

In get_capi_ctr_by_nr() and get_capi_appl_by_nr() the parameter comes
from skb->data.  The current code can underflow to one space before the
start of the array.

The sanity check isn't needed in __get_capi_appl_by_nr() but I changed
it to match the others.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c
index 9b1b274c7d25..c123709acf82 100644
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -93,7 +93,7 @@ capi_ctr_put(struct capi_ctr *ctr)
 
 static inline struct capi_ctr *get_capi_ctr_by_nr(u16 contr)
 {
-        if (contr - 1 >= CAPI_MAXCONTR)
+        if (contr < 1 || contr - 1 >= CAPI_MAXCONTR)
                 return NULL;
 
         return capi_controller[contr - 1];
@@ -103,7 +103,7 @@ static inline struct capi20_appl *__get_capi_appl_by_nr(u16 applid)
 {
         lockdep_assert_held(&capi_controller_lock);
 
-        if (applid - 1 >= CAPI_MAXAPPL)
+        if (applid < 1 || applid - 1 >= CAPI_MAXAPPL)
                 return NULL;
 
         return capi_applications[applid - 1];
@@ -111,7 +111,7 @@ static inline struct capi20_appl *__get_capi_appl_by_nr(u16 applid)
 
 static inline struct capi20_appl *get_capi_appl_by_nr(u16 applid)
 {
-        if (applid - 1 >= CAPI_MAXAPPL)
+        if (applid < 1 || applid - 1 >= CAPI_MAXAPPL)
                 return NULL;
 
         return rcu_dereference(capi_applications[applid - 1]);