tlv_put: guard against NULL val and 0 len

For example encode_auth_info() from gsup.c calls
  msgb_tlv_put(msg, iei, 0, NULL)
to put a tag and len with content data following later.

However, this would cause a memcpy() from a NULL pointer, in tlv_put(). Allow
passing NULL and len = 0 for cases like the above:

If val is NULL, use memset(0) instead of memcpy().
If len is zero, do not copy nor memset anything.

Hence make tlv_put() behave in a well-defined and valid way for any and all
input args; no negative fallout is possible from this patch.

Add proper API doc comment.

Fixes a sanitizer build failure in gsup_test:

  ../../../../src/libosmocore/include/osmocom/gsm/tlv.h:99:2: runtime error: null pointer passed as argument 2, which is declared to never be null

Helps fix sanitizer build on debian 9.

Change-Id: I13dce9cd1228817890d3e81edeeb660c893c1d64

0 files changed, 0 insertions, 0 deletions