sctp: validate STALE_COOKIE cause length before reading staleness

Overview

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

sctp: validate STALE_COOKIE cause length before reading staleness

When an ERROR chunk with a STALE_COOKIE cause is received in the COOKIE_ECHOED state, sctp_sf_do_5_2_6_stale() reads the 4-byte Measure of Staleness that follows the cause header:

err   = (struct sctp_errhdr *)(chunk->skb->data);
stale = ntohl(*(__be32 *)((u8 *)err + sizeof(*err)));

err is the first cause in the chunk, not the STALE_COOKIE cause that caused the dispatch, and nothing guarantees the staleness field is present. sctp_walk_errors() only requires a cause to be as long as the 4-byte header, so for a STALE_COOKIE cause of length 4 the read runs past the cause, and for a minimal ERROR chunk past skb->tail. The value is echoed to the peer in the Cookie Preservative of the reply INIT, leaking uninitialized memory.

sctp_sf_cookie_echoed_err() already walks to the STALE_COOKIE cause, so check its length there and pass it to sctp_sf_do_5_2_6_stale(), which reads that cause instead of the first one. A STALE_COOKIE cause too short to hold the staleness field is discarded.

The read is reachable by any peer that can drive an association into COOKIE_ECHOED, including an unprivileged process using a raw SCTP socket in a user and network namespace.

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6022da37786701df1fc5dd946a6dcba59d5473b1
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 861f884f5471632c731cbbd612a1c072e391a624
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 588706ebaf8cdb4a4161602949eba365514b1db1
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a257b41ddfe9e327b26581ad2777f04b23ac73f5
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 08a8f2d13f703924316e9aeac863a88ef50990c7
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ebe0a55d954fa8da383b6192edb8f763dcb002d5
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < bbd6b2ea966cf57b6ae095cf5a8dbc993cd197a0
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 1cd23ca80784223fa2204e16203f754da4e821f8
• Linux 2.6.12

Remediation

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