Review at  https://gerrit.osmocom.org/7840

prevent integer underflow in ipa_ccm_make_id_resp_from_req()

don't blindly trust the tag-length value in an IPA CCM ID GET
message.  This could result in a remotely-triggered integer underflow.

Change-Id: I4723361e1094b358310541a7dc4c5c921c778a15
---
M src/gsm/ipa.c
1 file changed, 6 insertions(+), 1 deletion(-)


  git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/40/7840/1

diff --git a/src/gsm/ipa.c b/src/gsm/ipa.c
index e03f615..0c7aaad 100644
--- a/src/gsm/ipa.c
+++ b/src/gsm/ipa.c
@@ -328,7 +328,12 @@
                ies[num_ies++] = t_tag;
 
                cur += t_len;
-               len -= t_len;
+               /* prevent any unsigned integer underflow due to somebody 
sending us
+                * messages with wrong length values */
+               if (len <= t_len)
+                       len -= t_len;
+               else
+                       len = 0;
        }
        return ipa_ccm_make_id_resp(dev, ies, num_ies);
 }

-- 
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I4723361e1094b358310541a7dc4c5c921c778a15
Gerrit-PatchSet: 1
Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Owner: Harald Welte <lafo...@gnumonks.org>

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