Re: [RFC PATCH 0/5] landlock: Pathname-based UNIX connect() control

["Günther Noack" <gnoack3000@gmail.com>]

On Fri, Jan 02, 2026 at 11:16:33AM +0100, Günther Noack wrote:
> Regarding the un-restrictable operations, Tingmao's pointers are
> correct.  In the warning box in the documentation, the missing
> operations that I am aware of are (a) the Unix socket connect()
> operation, and (b) the symlink lookup which happens implicitly during
> path traversal and which Landlock and other LSMs can not control
> through LSM hooks at the moment.  (A symlink always gets implicitly
> resolved during path lookup even when you do not have directory read
> permissions on the directory where the symlink is.)

I forgot to mention - the error codes returned by Landlock make it
possible to probe for the presence of files, even when all available
FS access rights are denied on a directory.  Attempting to open a file
for reading will return EEXIST if it is missing, but will return
EACCES if it is denied by Landlock.

gnoack:/tmp/xxx$ ls
foobar.txt
gnoack:/tmp/xxx$ landlock-restrict -rofiles /proc /usr /bin /etc/ -- /bin/cat foobar.txt
cat: foobar.txt: Permission denied
gnoack:/tmp/xxx$ landlock-restrict -rofiles /proc /usr /bin /etc/ -- /bin/cat nonexistent.txt
cat: nonexistent.txt: No such file or directory
gnoack:/tmp/xxx$ landlock-restrict -rofiles /proc /usr /bin /etc/ -- /bin/ls
ls: cannot open directory '.': Permission denied

–Günther