isdn/gigaset: fix zero size border case in debug dump

If subtracting 12 from l leaves zero we'd do a zero size allocation,
leading to an oops later when we try to set the NUL terminator.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/isdn/gigaset/capi.c b/drivers/isdn/gigaset/capi.c
index 68452b768da2..03a0a01a4054 100644
--- a/drivers/isdn/gigaset/capi.c
+++ b/drivers/isdn/gigaset/capi.c
@@ -248,6 +248,8 @@ static inline void dump_rawmsg(enum debuglevel level, const char *tag,
                 CAPIMSG_APPID(data), CAPIMSG_MSGID(data), l,
                 CAPIMSG_CONTROL(data));
         l -= 12;
+        if (l <= 0)
+                return;
         dbgline = kmalloc(3 * l, GFP_ATOMIC);
         if (!dbgline)
                 return;