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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
This commit is contained in:
Neels Hofmeyr 2017-11-16 23:34:33 +01:00
parent 85f5a2cd9c
commit e750980d6c
1 changed files with 13 additions and 2 deletions
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15
include/osmocom/gsm/tlv.h
View File

@ -90,13 +90,24 @@ static inline uint8_t *lv_put(uint8_t *buf, uint8_t len,
return buf + len;
}
/*! put (append) a TLV field */
/*! Append a TLV field, a Tag-Length-Value field.
* \param[out] buf Location in a buffer to append TLV at.
* \param[in] tag Tag id to write.
* \param[in] len Length field to write and amount of bytes to append.
* \param[in] val Pointer to data to append, or NULL to append zero data.
* Always append tag and length. Append \a len bytes read from \a val. If val is NULL, append \a len zero
* bytes instead. If \a len is zero, do not append any data apart from tag and length. */
static inline uint8_t *tlv_put(uint8_t *buf, uint8_t tag, uint8_t len,
const uint8_t *val)
{
*buf++ = tag;
*buf++ = len;
memcpy(buf, val, len);
if (len) {
if (val)
memcpy(buf, val, len);
else
memset(buf, 0, len);
}
return buf + len;
}