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Reporting Linux kernel bugs

Before reporting a bug make sure nobody else already reported it. The easiest way to do this is to search through the syzkaller mailing list, syzkaller-bugs mailing list and syzbot dashboard for key frames present in the kernel stack traces.

Please report found bugs to the Linux kernel maintainers. To find out the list of maintainers responsible for a particular kernel subsystem, use the get_maintainer.pl script: ./scripts/get_maintainer.pl -f guilty_file.c. Please add [email protected] to the CC list. Make sure to mention the exact kernel branch and revision where the bug occurred. Many kernel mailing lists reject HTML formatted messages, so use the plain text mode when sending the report.

Think of what you report. Today, Linux maintainers are overwhelmed with bug reports, so increasing the incoming flow won't help to fix all the bugs. The more actionable your report is, the higher the chance that it will be addressed. Note that people are more likely to care about kernel crashes (e.g. use-after-frees or panics) than of INFO: messages and such, unless it is clearly visible from the report what exactly is wrong. If there are stalls or hangs, only report them if they are frequent enough or have a reliable reproducer.

Overall, bugs without reproducers are way less likely to be triaged and fixed. If the bug is reproducible, include the reproducer (C source if possible, otherwise a syzkaller program) and the .config you used for your kernel. If the reprocucer is available only in the form of a syzkaller program, please link the instructions on how to execute them in your report. Check that the reproducer works if you run it manually. Syzkaller tries to simplify the reproducer, but the result might not be ideal. You can try to simplify or annotate the reproducer manually, that greatly helps kernel developers to figure out why the bug occurs.

If you want to get extra credit, you can try to undestand the bug and develop a fix yourself. If you can't figure out the right fix, but have some understanding of the bug, please add your thoughts and conclusions to the report, that will save some time for kernel developers.

Reporting security bugs

If you believe that a found bug poses potential security threat, consider following the instructions below. Note, that these instructions are a work-in-progress and based on my current undestanding of the disclosure proccess. This instruction is now being discussed here.

If you don't want to deal with this complex disclosure process you can either:

  1. Report the bug privately to [email protected]. In this case it should be fixed in the upstream kernel, but there are no guarantees that the fix will be propagated to stable or distro kernels. The maximum embargo on this list is 7 days.
  2. Report the bug privately to a vendor such as Red Hat ([email protected]) or SUSE ([email protected]). They should fix the bug, assign a CVE, and notify other vendors. The maximum embargo on these lists is 5 weeks.
  3. Report the bug publicly to [email protected].

If you want to deal with the disclosure yourself, read below.

The three main mailing lists for reporting and disclosing Linux kernel security issues are [email protected], [email protected] and [email protected]. The links for the guidelines for these lists are below, please read them carefully before sending anything to these lists.

  1. [email protected] - https://www.kernel.org/doc/html/latest/admin-guide/security-bugs.html
  2. [email protected] - http://oss-security.openwall.org/wiki/mailing-lists/distros
  3. [email protected] - http://oss-security.openwall.org/wiki/mailing-lists/oss-security

Reporting minor security bugs

To report minor security bugs (such as local DOS or local info leak):

  1. Report the bug publicly to kernel developers as described above and wait until a fix is committed. Alternatively, you can develop and send a fix yourself.
  2. Request a CVE from MITRE through the web form. Describe the bug details and add a link to the fix (from patchwork.kernel.org, git.kernel.org or github.com) in the request.
  3. Once a CVE is assigned, send the bug details, the CVE number and a link to the fix to [email protected].

Reporting major security bugs

To report major security bugs (such as LPE, remote DOS, remote info leak or RCE):

  1. Understand the bug and develop a patch with a fix if possible. Optionally develop a proof-of-concept exploit.
  2. Notify [email protected]:
    • Describe vulnerability details, include the proposed patch and optionally the exploit.
    • Ask for 7 days of embargo.
    • Work on the patch together with the [email protected] members.
  3. Notify [email protected]:
    • Describe vulnerability details, include the proposed patch and optionally the exploit.
    • Ask them to assign a CVE number.
    • Ask for 7 days of embargo.
  4. Wait 7 days for linux distros to apply the patch.
  5. Ask [email protected] to make the CVE description public and roll out the updated kernels.
  6. Send the fix upstream:
    • Mention the CVE number in the commit message.
    • Mention syzkaller in the commit message.
  7. Notify [email protected]:
    • Describe vulnerability details, include a link to the committed patch.
  8. Wait 1-3 days for people to update their kernels.
  9. Optionally publish the exploit on [email protected].

A few notes:

  • There should ideally be no delay between reports to [email protected] and [email protected].
  • When working on the patch together with the [email protected] members and upstream maintainers, keep the linux-distros aware of the progress.
  • There should ideally be no delay between CVE description publication, distros' updates, upstream commit and notification to [email protected]. All of these should be on the same day, at worst.
  • The moment the issue is made public (e.g. patch is submitted upstream, CVE description published, etc.) it must be reported to [email protected] right away.

A good example of an LPE announcement structure on [email protected] can be found here, however the timeline doesn't look right there: public announcement should have occurred right after the patch was submitted to netdev.