Commit 54a46387 authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont
Browse files

Fix SRTP Roll-Over-Counter handling

parent a7c26dab
......@@ -387,13 +387,45 @@ rtp_crypt (gcry_cipher_hd_t hd, uint32_t ssrc, uint32_t roc, uint16_t seq,
}
/** Determines SRTP Roll-Over-Counter (in host-byte order) */
static uint32_t
srtp_compute_roc (const srtp_session_t *s, uint16_t seq)
{
uint32_t roc = s->rtp_roc;
if (((seq - s->rtp_seq) & 0xffff) < 0x8000)
{
/* Sequence is ahead, good */
if (seq < s->rtp_seq)
roc++; /* Sequence number wrap */
}
else
{
/* Sequence is late, bad */
if (seq > s->rtp_seq)
roc--; /* Wrap back */
}
return roc;
}
/** Returns RTP sequence (in host-byte order) */
static inline uint16_t rtp_seq (const uint8_t *buf)
{
return (buf[2] << 8) | buf[3];
}
/** Message Authentication and Integrity for RTP */
static const uint8_t *
rtp_digest (gcry_md_hd_t md, const void *data, size_t len, uint32_t roc)
rtp_digest (srtp_session_t *s, const uint8_t *data, size_t len)
{
const gcry_md_hd_t md = s->rtp.mac;
uint32_t roc = htonl (srtp_compute_roc (s, rtp_seq (data)));
gcry_md_reset (md);
gcry_md_write (md, data, len);
gcry_md_write (md, &(uint32_t){ htonl (roc) }, 4);
gcry_md_write (md, &roc, 4);
return gcry_md_read (md, 0);
}
......@@ -436,27 +468,22 @@ static int srtp_crypt (srtp_session_t *s, uint8_t *buf, size_t len)
return EINVAL;
/* Determines RTP 48-bits counter and SSRC */
uint32_t ssrc;
uint16_t seq = rtp_seq (buf);
uint32_t roc = srtp_compute_roc (s, seq), ssrc;
memcpy (&ssrc, buf + 8, 4);
uint16_t seq = (buf[2] << 8) | buf[3];
if (((seq - s->rtp_seq) & 0xffff) < 32768)
{
if (seq < s->rtp_seq)
s->rtp_roc++; /* Sequence number wrap */
}
/* Updates ROC and sequence (it's safe now) */
if (roc > s->rtp_roc)
s->rtp_seq = seq, s->rtp_roc = roc;
else
{
if (seq > s->rtp_seq)
s->rtp_roc--;
}
s->rtp_seq = seq;
if (seq > s->rtp_seq)
s->rtp_seq = seq;
/* Encrypt/Decrypt */
if (s->flags & SRTP_UNENCRYPTED)
return 0;
if (rtp_crypt (s->rtp.cipher, ssrc, s->rtp_roc, seq, s->rtp.salt,
if (rtp_crypt (s->rtp.cipher, ssrc, roc, seq, s->rtp.salt,
buf + offset, len - offset))
return EINVAL;
......@@ -486,15 +513,15 @@ srtp_send (srtp_session_t *s, uint8_t *buf, size_t *lenp, size_t bufsize)
if (val)
return val;
if (s->flags & SRTP_UNAUTHENTICATED)
return 0;
if (bufsize < (len + s->tag_len))
return ENOSPC;
if (!(s->flags & SRTP_UNAUTHENTICATED))
{
if (bufsize < (len + s->tag_len))
return ENOSPC;
const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, s->rtp_roc);
memcpy (buf + len, tag, s->tag_len);
*lenp = len + s->tag_len;
const uint8_t *tag = rtp_digest (s, buf, len);
memcpy (buf + len, tag, s->tag_len);
*lenp = len + s->tag_len;
}
return 0;
}
......@@ -520,11 +547,11 @@ srtp_recv (srtp_session_t *s, uint8_t *buf, size_t *lenp)
if (!(s->flags & SRTP_UNAUTHENTICATED))
{
if (len < s->tag_len)
if (len < (12u + s->tag_len))
return EINVAL;
len -= s->tag_len;
const uint8_t *tag = rtp_digest (s->rtp.mac, buf, len, s->rtp_roc);
const uint8_t *tag = rtp_digest (s, buf, len);
if (memcmp (buf + len, tag, s->tag_len))
return EACCES;
......
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