On 8/19/26 1:38 AM, Martin Kletzander wrote:
On Tue, Aug 18, 2026 at 03:53:58PM -0600, Jim Fehlig via Devel wrote:
From: Jim Fehlig <[email protected]>
libvirt chown()s the swtpm log file to the swtpm user:group when starting
a VM. The swtpm log directory is writable by swtmp user, who could replace
the logfile with a symlink to a root-owned path. At next VM start, libvirt
will chown() that path to the swtpm user:group, which breaks the intended
separation between the confined swtpm account and root-owned files.
Use fchown() on an fd opened with O_NOFOLLOW to avoid the potential
symlink attack.
I thought the O_NOFOLLOW was a BSDism and went to check whether it is
POSIX or not. I looked at the man page and instantly felt old.
Same. I knew Linux supported it for a while, but didn't think that many years
have raced by :-)
"This flag is a FreeBSD extension, which was added in Linux 2.1.126, and has
subsequently been standardized in POSIX.1-2008"
Cheers,
Jim
