FreeBSD Security Advisories
2021-Jan-29 02:28 UTC
[FreeBSD-Announce] FreeBSD Security Advisory FreeBSD-SA-21:01.fsdisclosure
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============================================================================FreeBSD-SA-21:01.fsdisclosure
Security Advisory
The FreeBSD Project
Topic: Uninitialized kernel stack leaks in several file systems
Category: core
Module: fs
Announced: 2021-01-29
Credits: Syed Faraz Abrar
Affects: All supported versions of FreeBSD.
Corrected: 2021-01-06 14:58:41 UTC (stable/12, 12.2-STABLE)
2021-01-29 01:20:59 UTC (releng/12.2, 12.2-RELEASE-p3)
2021-01-29 01:06:09 UTC (releng/12.1, 12.1-RELEASE-p13)
2021-01-18 19:16:24 UTC (stable/11, 11.4-STABLE)
2021-01-29 00:20:09 UTC (releng/11.4, 11.4-RELEASE-p7)
CVE Name: CVE-2020-25578, CVE-2020-25579
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.
I. Background
The FreeBSD kernel exports file system directory entries to userspace
using the generic "dirent" structure. Individual file systems
implement
VOP_READDIR to convert from the file system's internal directory entry
layout to the generic form. dirent structures can be fetched from
userspace using the getdirentries(2) system call.
II. Problem Description
Several file systems were not properly initializing the d_off field of
the dirent structures returned by VOP_READDIR. In particular, tmpfs(5),
smbfs(5), autofs(5) and mqueuefs(5) were failing to do so. As a result,
eight uninitialized kernel stack bytes may be leaked to userspace by
these file systems. This problem is not present in FreeBSD 11.
Additionally, msdosfs(5) was failing to zero-fill a pair of padding
fields in the dirent structure, resulting in a leak of three
uninitialized bytes.
III. Impact
Kernel stack disclosures may leak sensitive information which could be
used to compromise the security of the system.
IV. Workaround
Systems that do not have any of the affected file systems mounted are
not affected. To trigger the leaks, an unprivileged user must have read
access to a directory belonging to one of the mounted file systems.
V. Solution
Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.
Perform one of the following:
1) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"
2) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
[FreeBSD 12.x]
# fetch https://security.FreeBSD.org/patches/SA-21:01/fsdisclosure.12.patch
# fetch https://security.FreeBSD.org/patches/SA-21:01/fsdisclosure.12.patch.asc
# gpg --verify fsdisclosure.12.patch.asc
[FreeBSD 11.x]
# fetch https://security.FreeBSD.org/patches/SA-21:01/fsdisclosure.11.patch
# fetch https://security.FreeBSD.org/patches/SA-21:01/fsdisclosure.11.patch.asc
# gpg --verify fsdisclosure.11.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.
VI. Correction details
The following list contains the correction revision numbers for each
affected branch.
Branch/path Revision
- -------------------------------------------------------------------------
stable/12/ r368969
releng/12.2/ r369175
releng/12.1/ r369165
stable/11/ r369047
releng/11.4/ r369156
- -------------------------------------------------------------------------
To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:
# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
VII. References
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-25578>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-25579>
The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-21:01.fsdisclosure.asc>
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Miroslav Lachman
2021-Jan-31 11:29 UTC
[FreeBSD-Announce] FreeBSD Security Advisory FreeBSD-SA-21:01.fsdisclosure
On 29/01/2021 03:28, FreeBSD Security Advisories wrote:> -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA512 > > ============================================================================> FreeBSD-SA-21:01.fsdisclosure Security Advisory > The FreeBSD Project > > Topic: Uninitialized kernel stack leaks in several file systems > > Category: core > Module: fs > Announced: 2021-01-29 > Credits: Syed Faraz Abrar > Affects: All supported versions of FreeBSD. > Corrected: 2021-01-06 14:58:41 UTC (stable/12, 12.2-STABLE) > 2021-01-29 01:20:59 UTC (releng/12.2, 12.2-RELEASE-p3) > 2021-01-29 01:06:09 UTC (releng/12.1, 12.1-RELEASE-p13) > 2021-01-18 19:16:24 UTC (stable/11, 11.4-STABLE) > 2021-01-29 00:20:09 UTC (releng/11.4, 11.4-RELEASE-p7) > CVE Name: CVE-2020-25578, CVE-2020-25579 > > For general information regarding FreeBSD Security Advisories, > including descriptions of the fields above, security branches, and the > following sections, please visit <URL:https://security.FreeBSD.org/>. > > I. Background > > The FreeBSD kernel exports file system directory entries to userspace > using the generic "dirent" structure. Individual file systems implement > VOP_READDIR to convert from the file system's internal directory entry > layout to the generic form. dirent structures can be fetched from > userspace using the getdirentries(2) system call. > > II. Problem Description > > Several file systems were not properly initializing the d_off field of > the dirent structures returned by VOP_READDIR. In particular, tmpfs(5), > smbfs(5), autofs(5) and mqueuefs(5) were failing to do so. As a result, > eight uninitialized kernel stack bytes may be leaked to userspace by > these file systems. This problem is not present in FreeBSD 11.There is a Corrected in: stable/11, 11.4-STABLE and releng/11.4, 11.4-RELEASE-p7, but later is a statement "This problem is not present in FreeBSD 11". What is true? Is it fixed in newer patchlevel of FreeBSD 11.4 or it was not present in 11.x at all? Kind regards Miroslav Lachman