cgroup: Use separate src/dst nodes when preloading css_sets for migration

Description

In the Linux kernel, the following vulnerability has been resolved: cgroup: Use separate src/dst nodes when preloading css_sets for migration Each cset (css_set) is pinned by its tasks. When we're moving tasks around across csets for a migration, we need to hold the source and destination csets to ensure that they don't go away while we're moving tasks about. This is done by linking cset->mg_preload_node on either the mgctx->preloaded_src_csets or mgctx->preloaded_dst_csets list. Using the same cset->mg_preload_node for both the src and dst lists was deemed okay as a cset can't be both the source and destination at the same time. Unfortunately, this overloading becomes problematic when multiple tasks are involved in a migration and some of them are identity noop migrations while others are actually moving across cgroups. For example, this can happen with the following sequence on cgroup1: #1> mkdir -p /sys/fs/cgroup/misc/a/b #2> echo $$ > /sys/fs/cgroup/misc/a/cgroup.procs #3> RUN_A_COMMAND_WHICH_CREATES_MULTIPLE_THREADS & #4> PID=$! #5> echo $PID > /sys/fs/cgroup/misc/a/b/tasks #6> echo $PID > /sys/fs/cgroup/misc/a/cgroup.procs the process including the group leader back into a. In this final migration, non-leader threads would be doing identity migration while the group leader is doing an actual one. After #3, let's say the whole process was in cset A, and that after #4, the leader moves to cset B. Then, during #6, the following happens: 1. cgroup_migrate_add_src() is called on B for the leader. 2. cgroup_migrate_add_src() is called on A for the other threads. 3. cgroup_migrate_prepare_dst() is called. It scans the src list. 4. It notices that B wants to migrate to A, so it tries to A to the dst list but realizes that its ->mg_preload_node is already busy. 5. and then it notices A wants to migrate to A as it's an identity migration, it culls it by list_del_init()'ing its ->mg_preload_node and putting references accordingly. 6. The rest of migration takes place with B on the src list but nothing on the dst list. This means that A isn't held while migration is in progress. If all tasks leave A before the migration finishes and the incoming task pins it, the cset will be destroyed leading to use-after-free. This is caused by overloading cset->mg_preload_node for both src and dst preload lists. We wanted to exclude the cset from the src list but ended up inadvertently excluding it from the dst list too. This patch fixes the issue by separating out cset->mg_preload_node into ->mg_src_preload_node and ->mg_dst_preload_node, so that the src and dst preloadings don't interfere with each other.

Timeline

Scores

EPSS (exploitation in 30 days)

0.29% · top 78% of all CVEs (7 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.

Weakness

• CWE-416 Use After Free (opens in a new tab)All about CWE-416 and its CVEs

Affected products

• Linux · Linux

  • affected f817de98513d060023be4fa1d061b29a6515273e – < 05f7658210d1d331e8dd4cb6e7bbbe3df5f5ac27
  • affected f817de98513d060023be4fa1d061b29a6515273e – < cec2bbdcc14fbaa6b95ee15a7c423b05d97038be
  • affected f817de98513d060023be4fa1d061b29a6515273e – < ad44e05f3e016bdcb1ad25af35ade5b5f41ccd68
  • affected f817de98513d060023be4fa1d061b29a6515273e – < 7657e3958535d101a24ab4400f9b8062b9107cc4
  • affected f817de98513d060023be4fa1d061b29a6515273e – < 54aee4e5ce8c21555286a6333e46c1713880cf93
  • affected f817de98513d060023be4fa1d061b29a6515273e – < 0e41774b564befa6d271e8d5086bf870d617a4e6
  • affected f817de98513d060023be4fa1d061b29a6515273e – < 07fd5b6cdf3cc30bfde8fe0f644771688be04447

• Linux · Linux

  • affected 3.16
  • unaffected < 3.16
  • unaffected 4.14.289 – ≤ 4.14.*
  • unaffected 4.19.253 – ≤ 4.19.*
  • unaffected 5.4.207 – ≤ 5.4.*
  • unaffected 5.10.132 – ≤ 5.10.*
  • unaffected 5.15.56 – ≤ 5.15.*
  • unaffected 5.18.13 – ≤ 5.18.*
  • unaffected 5.19 – ≤ *

References (7)

• https://git.kernel.org/stable/c/05f7658210d1d331e8dd4cb6e7bbbe3df5f5ac27 (opens in a new tab)
• https://git.kernel.org/stable/c/cec2bbdcc14fbaa6b95ee15a7c423b05d97038be (opens in a new tab)
• https://git.kernel.org/stable/c/ad44e05f3e016bdcb1ad25af35ade5b5f41ccd68 (opens in a new tab)
• https://git.kernel.org/stable/c/7657e3958535d101a24ab4400f9b8062b9107cc4 (opens in a new tab)
• https://git.kernel.org/stable/c/54aee4e5ce8c21555286a6333e46c1713880cf93 (opens in a new tab)
• https://git.kernel.org/stable/c/0e41774b564befa6d271e8d5086bf870d617a4e6 (opens in a new tab)
• https://git.kernel.org/stable/c/07fd5b6cdf3cc30bfde8fe0f644771688be04447 (opens in a new tab)

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2022-49647](https://trackcve.app/badge/CVE-2022-49647.svg)](https://trackcve.app/cve/CVE-2022-49647)

Record last updated 5 Aug 2026, 08:55 UTC.