sctp: hold socket lock when dumping endpoints in sctp_diag

Overview

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

sctp: hold socket lock when dumping endpoints in sctp_diag

SCTP_DIAG endpoint dumping was traversing endpoint address lists without holding lock_sock(), while those lists could change concurrently via socket operations (e.g., bindx changes). This creates a race where nla_reserve() counts addresses under RCU protection, but the subsequent copy may see fewer entries, potentially leaking uninitialized memory to userspace.

Fix this by:

• Taking a reference on each endpoint during hash traversal
• Moving socket operations (lock_sock()) outside read_lock_bh()
• Serializing address list access during dump
• Reworking sctp_for_each_endpoint() to support restart-based traversal with (net, pos) tracking

Also:

• Add WARN_ON_ONCE() for inconsistent address counts
• Fix idiag_states filtering for LISTEN vs association cases
• Skip dumping endpoints being freed (ep->base.dead)
• Move dump position tracking into iterator, removing cb->args[4] and its comment for sctp_ep_dump().,
• Update the comment for cb->args[4] and remove the comment for unused cb->args[5] for sctp_sock_dump().

Note: traversal is restart-based and may re-scan buckets multiple times, but this is acceptable due to small bucket sizes and required to support sleeping-safe callbacks.

This issue was reported by Nico Yip (@cyeaa) working with TrendAI Zero Day Initiative.

Affected

• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < f98c294a9369b6fe89e652c06357ee594be4dfa2
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < 8b38e3dcfde3077dbc03eb8ef88e03cc19f70b8a
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < ec3c2d59a192e17e1014ba71afc368ba162ecac3
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < 722576aba0a6d9423714550b1c03239b0f0def77
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < abe7f8828e6ac8be858870c2bf836258844f97d5
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < 207bb4ce8fe7de961ae7bb33569ad2cd61f44954
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < f09a245f33e567b604efa1960b7a2d25dd9c8713
• Linux >= 8f840e47f190cbe61a96945c13e9551048d42cef < 7d8297e26b4e20b5d1c3c3fe51fe81a1c7fbc823
• Linux 4.7

Remediation

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