CVE-2021-29155
First published: Sun Apr 18 2021(Updated: )
A vulnerability was discovered in retrieve_ptr_limit in kernel/bpf/verifier.c in the Linux kernel mechanism to mitigate speculatively out-of-bounds loads (Spectre mitigation). In this flaw a local, special user privileged (CAP_SYS_ADMIN) BPF program running on affected systems may bypass the protection, and execute speculatively out-of-bounds loads from the kernel memory. This can be abused to extract contents of kernel memory via side-channel.
Credit: cve@mitre.org cve@mitre.org cve@mitre.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| redhat/kernel-rt | <0:4.18.0-348.rt7.130.el8 | 0:4.18.0-348.rt7.130.el8 |
| redhat/kernel | <0:4.18.0-348.el8 | 0:4.18.0-348.el8 |
| Linux Linux kernel | <5.11.16 | |
| Fedoraproject Fedora | =32 | |
| Fedoraproject Fedora | =33 | |
| Fedoraproject Fedora | =34 | |
| Debian Debian Linux | =9.0 | |
| redhat/Kernel | <5.12 | 5.12 |
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.119-1 6.11.10-1 6.12.5-1 |
Remedy
The default Red Hat Enterprise Linux kernel prevents unprivileged users from being able to use eBPF by the kernel.unprivileged_bpf_disabled sysctl. This would require a privileged user with CAP_SYS_ADMIN or root to be able to abuse this flaw reducing its attack space. For the Red Hat Enterprise Linux 7 the eBPF for unprivileged users is always disabled. For the Red Hat Enterprise Linux 8 to confirm the current state, inspect the sysctl with the command: # cat /proc/sys/kernel/unprivileged_bpf_disabled The setting of 1 would mean that unprivileged users can not use eBPF, mitigating the flaw. A kernel update will be required to mitigate the flaw for the root or users with CAP_SYS_ADMIN capabilities.
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Reference Links
- https://www.cve.org/CVERecord?id=CVE-2021-29155 https://nvd.nist.gov/vuln/detail/CVE-2021-29155 https://www.openwall.com/lists/oss-security/2021/04/18/4
- https://bugzilla.redhat.com/show_bug.cgi?id=1951595
- https://access.redhat.com/errata/RHSA-2021:4140
- https://access.redhat.com/errata/RHSA-2021:4356
- https://access.redhat.com/security/cve/cve-2021-29155
- https://lists.debian.org/debian-lts-announce/2021/06/msg00019.html
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/CUX2CA63453G34C6KYVBLJXJXEARZI2X/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/PAEQ3H6HKNO6KUCGRZVYSFSAGEUX23JL/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XZASHZVCOFJ4VU2I3BN5W5EPHWJQ7QWX/
- https://www.kernel.org
- https://www.openwall.com/lists/oss-security/2021/04/18/4
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=1951597
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=073815b756c51ba9d8384d924c5d1c03ca3d1ae4
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=24c109bb1537c12c02aeed2d51a347b4d6a9b76e
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6f55b2f2a1178856c19bbce2f71449926e731914
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7fedb63a8307dda0ec3b8969a3b233a1dd7ea8e0
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=9601148392520e2e134936e76788fc2a6371e7be
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=a6aaece00a57fa6f22575364b3903dfbccf5345d
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=b658bbb844e28f1862867f37e8ca11a8e2aa94a3
- https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=f528819334881fd622fdadeddb3f7edaed8b7c9b
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CUX2CA63453G34C6KYVBLJXJXEARZI2X/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PAEQ3H6HKNO6KUCGRZVYSFSAGEUX23JL/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XZASHZVCOFJ4VU2I3BN5W5EPHWJQ7QWX/
- https://launchpad.net/bugs/cve/CVE-2021-29155
- https://lore.kernel.org/stable/215e98bf-21c7-0074-129d-49a51526418b@iogearbox.net/
- https://security-tracker.debian.org/tracker/CVE-2021-29155
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-29155
- https://nvd.nist.gov/vuln/detail/CVE-2021-29155
- https://ubuntu.com/security/CVE-2021-29155
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