netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp

Overview

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nf_conntrack_sip: fix use of uninitialized rtp_addr in process_sdp

process_sdp() declares union nf_inet_addr rtp_addr on the stack and passes it to the nf_nat_sip sdp_session hook after walking the SDP media descriptions. However rtp_addr is only initialized inside the media loop when a recognized media type with a non-zero port is found.

If the SDP body contains no m= lines, only inactive media sections (m=audio 0 ...) or only unrecognized media types, rtp_addr is never assigned. Despite that, the function still calls hooks->sdp_session() with &rtp_addr, causing nf_nat_sdp_session() to format the stale stack value as an IP address and rewrite the SDP session owner and connection lines with it.

With CONFIG_INIT_STACK_ALL_ZERO (default on most distributions) this results in the session-level o= and c= addresses being rewritten to 0.0.0.0 for inactive SDP sessions. Without stack auto-init the rewritten address is whatever happened to be on the stack.

Fix this by pre-initializing rtp_addr from the session-level connection address (caddr) when available, and tracking via a have_rtp_addr flag whether any valid address was established. Skip the sdp_session hook entirely when no valid address exists.

Affected

• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < faa6ea32797a1847790514ff0da1be1d09771580
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 82baeb871e8f04906bc886273fdf0209e1754eb3
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 6e5e3c87b7e6212f1d8414fc2e4d158b01e12025
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < fe463e76c9b4b0b43b5ee8961b4c500231f1a3f6
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 7edca70751b9bdb5b83eed53cde21eccf3c86147
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 01f34a80ac23ae90b1909b94b4ed05343a62f646
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 52fdda318ef2362fc5936385bcb8b3d0328ee629
• Linux >= 4ab9e64e5e3c0516577818804aaf13a630d67bc9 < 6a2b724460cb67caed500c508c2ae5cf012e4db4
• Linux 2.6.26

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.