AmSdp::parse: contain parser exceptions instead of aborting on malformed SDP

[hecko]

Bug

parse_sdp_line_ex() and its helpers in core/AmSdp.cpp build std::string objects from raw pointer arithmetic with no lower-bound guard, for example:

c.address = string(connection_line, line_len - 7);              // IP4/IP6 c-line
c.address = string(connection_line, int(next - connection_line) - 2);
media     = string(media_line, int(next - media_line) - 1);

line_len is a size_t. On a truncated or malformed line (e.g. a c= line shorter than the assumed IN IPx prefix) line_len - 7 underflows to a huge value, and std::string throws std::length_error. The pointer-difference forms can likewise go negative and convert to a huge size_t.

AmSdp::parse() is called directly on attacker-supplied INVITE/UPDATE offer and answer bodies, and its callers do not catch. An unhandled throw propagates out of the SIP processing path and terminates the process — a remotely-triggerable DoS via a single crafted SDP body.

Fix

Wrap the parse_sdp_line_ex() call in try/catch and report a parse failure (return non-zero, matching the file's existing error-return convention) instead of letting the exception escape:

bool ret = true;
try {
  ret = parse_sdp_line_ex(this, s);
} catch(const std::exception& e) {
  ERROR("exception while parsing SDP: %s\n", e.what());
  return true;
} catch(...) {
  ERROR("unknown exception while parsing SDP\n");
  return true;
}

<stdexcept> is already included. No behavioural change for well-formed SDP.

Provenance

Backported from yeti-switch/sems, which guards the same parse_sdp_line_ex() call with try/catch for std::out_of_range and generic exceptions. Thanks to the yeti-switch maintainers for the fix.

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Generated by Claude Code

[Copilot]

Pull request overview

This PR hardens SDP parsing against malformed/truncated attacker-supplied SDP bodies by containing exceptions thrown during parsing, preventing an unhandled exception from terminating the SIP processing process (remotely-triggerable DoS).

Changes:

• Wrap parse_sdp_line_ex() inside AmSdp::parse() in try/catch to prevent exceptions from escaping the SIP path.
• Log parsing exceptions and return a non-zero parse error (consistent with AmSdp::parse()’s !=0 error contract).
• Add in-code rationale documenting why exception containment is required for security/robustness.

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