| From bippy-8e903de6a542 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2021-47488: cgroup: Fix memory leak caused by missing cgroup_bpf_offline |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| cgroup: Fix memory leak caused by missing cgroup_bpf_offline |
| |
| When enabling CONFIG_CGROUP_BPF, kmemleak can be observed by running |
| the command as below: |
| |
| $mount -t cgroup -o none,name=foo cgroup cgroup/ |
| $umount cgroup/ |
| |
| unreferenced object 0xc3585c40 (size 64): |
| comm "mount", pid 425, jiffies 4294959825 (age 31.990s) |
| hex dump (first 32 bytes): |
| 01 00 00 80 84 8c 28 c0 00 00 00 00 00 00 00 00 ......(......... |
| 00 00 00 00 00 00 00 00 6c 43 a0 c3 00 00 00 00 ........lC...... |
| backtrace: |
| [<e95a2f9e>] cgroup_bpf_inherit+0x44/0x24c |
| [<1f03679c>] cgroup_setup_root+0x174/0x37c |
| [<ed4b0ac5>] cgroup1_get_tree+0x2c0/0x4a0 |
| [<f85b12fd>] vfs_get_tree+0x24/0x108 |
| [<f55aec5c>] path_mount+0x384/0x988 |
| [<e2d5e9cd>] do_mount+0x64/0x9c |
| [<208c9cfe>] sys_mount+0xfc/0x1f4 |
| [<06dd06e0>] ret_fast_syscall+0x0/0x48 |
| [<a8308cb3>] 0xbeb4daa8 |
| |
| This is because that since the commit 2b0d3d3e4fcf ("percpu_ref: reduce |
| memory footprint of percpu_ref in fast path") root_cgrp->bpf.refcnt.data |
| is allocated by the function percpu_ref_init in cgroup_bpf_inherit which |
| is called by cgroup_setup_root when mounting, but not freed along with |
| root_cgrp when umounting. Adding cgroup_bpf_offline which calls |
| percpu_ref_kill to cgroup_kill_sb can free root_cgrp->bpf.refcnt.data in |
| umount path. |
| |
| This patch also fixes the commit 4bfc0bb2c60e ("bpf: decouple the lifetime |
| of cgroup_bpf from cgroup itself"). A cgroup_bpf_offline is needed to do a |
| cleanup that frees the resources which are allocated by cgroup_bpf_inherit |
| in cgroup_setup_root. |
| |
| And inside cgroup_bpf_offline, cgroup_get() is at the beginning and |
| cgroup_put is at the end of cgroup_bpf_release which is called by |
| cgroup_bpf_offline. So cgroup_bpf_offline can keep the balance of |
| cgroup's refcount. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47488 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.3 with commit 4bfc0bb2c60e and fixed in 5.10.77 with commit 01599bf7cc2b |
| Issue introduced in 5.3 with commit 4bfc0bb2c60e and fixed in 5.14.16 with commit b529f88d9388 |
| Issue introduced in 5.3 with commit 4bfc0bb2c60e and fixed in 5.15 with commit 04f8ef5643bc |
| Issue introduced in 5.3 with commit 4bfc0bb2c60e and fixed in 6.11.11 with commit 966666b70b86 |
| Issue introduced in 5.3 with commit 4bfc0bb2c60e and fixed in 6.12.2 with commit dd6ade970de9 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2021-47488 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| kernel/cgroup/cgroup.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/01599bf7cc2b49c3d2be886cb438647dc25446ed |
| https://git.kernel.org/stable/c/b529f88d93884cf8ccafda793ee3d27b82fa578d |
| https://git.kernel.org/stable/c/04f8ef5643bcd8bcde25dfdebef998aea480b2ba |
| https://git.kernel.org/stable/c/966666b70b86c96843c4e143bd59c83e3082d1b4 |
| https://git.kernel.org/stable/c/dd6ade970de9378ad86ef027c1a6b9ef15e2d393 |
