An attacker could race with us during mount configuration in order to
trick us into mounting over an unexpected path. This would bypass
checkProcMount() and would allow for security profiles to be left
unapplied by mounting over /proc/self/attr/... (or even more serious
outcomes such as killing the entire system by tricking runc into writing
strings to /proc/sysrq-trigger).
This is a larger issue with our current mount infrastructure, and the
ideal solution would be to rewrite it all to be fd-based (which would
also allow us to support the "new" mount API, which also avoids a bunch
of other issues with mount(8)). However, such a rewrite is not really
workable as a security fix, so this patch is a bit of a compromise
approach to fix the issue while also moving us a bit towards that
eventual end-goal.
The core issue in CVE-2025-52881 is that we currently use the (insecure)
SecureJoin to re-resolve mountpoint target paths multiple times during
mounting. Rather than generating a string from createMountpoint(), we
instead open an *os.File handle to the target mountpoint directly and
then operate on that handle. This will make it easier to remove
utils.WithProcfd() and rework mountViaFds() in the future.
The only real issue we need to work around is that we need to re-open
the mount target after doing the mount in order to get a handle to the
mountpoint -- pathrs.Reopen() doesn't work in this case (it just
re-opens the inode under the mountpoint) so we need to do a naive
re-open using the full path. Note that if we used move_mount(2) this
wouldn't be a problem because we would have a handle to the mountpoint
itself.
Note that this is still somewhat of a temporary solution -- ideally
mountViaFds would use *os.File directly to let us avoid some other
issues with using bare /proc/... paths, as well as also letting us more
easily use the new mount API on modern kernels.
Fixes: GHSA-cgrx-mc8f-2prm CVE-2025-52881
Co-developed-by: lifubang <lifubang@acmcoder.com>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
sysctls could in principle also be used as a write gadget for arbitrary
procfs files. As this requires getting a non-subset=pid /proc handle we
amortise this by only allocating a single procfs handle for all sysctl
writes.
Fixes: GHSA-cgrx-mc8f-2prm CVE-2025-52881
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
All of the callers of EnsureProcHandle now use filepath-securejoin's
ProcThreadSelf to get a file handle, which has much stricter
verification to avoid procfs attacks than EnsureProcHandle's very
simplistic filesystem type check.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
From a safety perspective this might not be strictly required, but it
paves the way for us to remove utils.ProcThreadSelf.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
EnsureProcHandle only protects us against a tmpfs mount, but the risk of
a procfs path being used (such as /proc/self/sched) has been known for a
while. Now that filepath-securejoin has a reasonably safe procfs API,
switch to it.
Fixes: GHSA-cgrx-mc8f-2prm CVE-2025-52881
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
os.Create is shorthand for open(O_CREAT|O_TRUNC) *without* O_EXCL, which
is incredibly unsafe for us to do when interacting with a container
rootfs (especially before pivot_root) as an attacker could swap the
target path with a symlink that points to the host filesystem, causing
us to delete the contents of or create host files.
We did have a similar bug in CVE-2024-45310, but in that case we
(luckily) didn't have O_TRUNC set which avoided the worst possible case.
However, os.Create does set O_TRUNC and we were using it in scenarios
that may have been exploitable.
Because of how easy it us for us to accidentally introduce this kind of
bug, we should simply not allow the usage of os.Create in our entire
codebase.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
If an attacker were to make the target of a device inode creation be a
symlink to some host path, os.Create would happily truncate the target
which could lead to all sorts of issues. This exploit is probably not as
exploitable because device inodes are usually only bind-mounted for
rootless containers, which cannot overwrite important host files (though
user files would still be up for grabs).
The regular inode creation logic could also theoretically be tricked
into changing the access mode and ownership of host files if the
newly-created device inode was swapped with a symlink to a host path.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
In order to avoid lint errors due to the deprecation of the top-level
securejoin methods ported from libpathrs, we need to adjust
internal/pathrs to use the new pathrs-lite subpackage instead.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
This is primarily done out of an abudance of caution against runc exec
being attacked by a container where /dev/pts/ptmx has been replaced with
some other bad inode (a disconnected NFS handle, a symlink that goes
through a leaked runc file descriptor to reference a host ptmx, etc).
Unfortunately, we cannot trivially verify that /dev/pts/ptmx is actually
the /dev/pts from the container without storing stuff like the fsid in
the runc state.json, which is probably not worth the extra effort. This
should at least avoid the most concerning cases.
Reported-by: Aleksa Sarai <cyphar@cyphar.com>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
An attacker could make /dev/console a symlink. This presents two
possible issues:
1. os.Create will happily truncate targets, which could have resulted
in a worse version of CVE-2024-4531. Luckily, this all happens after
pivot_root(2) so the scope of that particular attack is fairly
limited (you are unlikely to be able to easily access host rootfs
files -- though it might be possible to take advantage of leaks such
as in CVE-2024-21626). However, O_CREAT|O_NOFOLLOW is what we should
be doing for all file creations.
2. Because we passed /dev/console as the only mount path (as opposed to
using a /proc/self/fd/$n path), an attacker could swap the symlink
to point to any other path and thus cause us to mount over some
other path. This is not as big of a problem because all the mounts
are in the container namespace after pivot_root(2), and users
usually can create arbitrary mount targets inside the container.
These issues don't seem particularly exploitable, but they deserve to be
hardened regardless.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
The pty driver has very consistent allocation rules for the major:minor
numbers of /dev/pts/$n inodes, so it is possible to somewhat safely open
/dev/pts/* paths if we validate that the inode is the one we expect.
It is possible for an attacker to have over-mounted a pts peer from a
different devpts instance, but to fix this would require more tracking
of devpts instances than runc currently can do.
This means runc should continue to work on very old kernels.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
When opening the peer end of a pty, the old kernel API required us to
open /dev/pts/$num inside the container (at least since we fixed console
handling many years ago in commit 244c9fc426 ("*: console rewrite")).
The problem is that in a hostile container it is possible for
/dev/pts/$num to be an attacker-controlled symlink that runc can be
tricked into resolving when doing bind-mounts. This allows the attacker
to (among other things) persist /proc/... entries that are later masked
by runc, allowing an attacker to escape through the kernel.core_pattern
sysctl (/proc/sys/kernel/core_pattern). This is the original issue
reported by Lei Wang and Li Fu Bang in CVE-2025-52565.
However, it should be noted that this is not entirely a newly-discovered
problem. Way back in Linux 4.13 (2017), I added the TIOCGPTPEER ioctl,
which allows us to get a pty peer without touching the /dev/pts inside
the container. The original threat model was around an attacker
replacing /dev/pts/$n or /dev/pts/ptmx with some malicious inode (a DoS
inode, or possibly a PTY they wanted a confused deputy to operate on).
Unfortunately, there was no practical way for runc to cache a safe
O_PATH handle to /dev/pts/ptmx (unlike other runtimes like LXC, which
switched to TIOCGPTPEER way back in 2017). Since it wasn't clear how we
could protect against the main attack TIOCGPTPEER was meant to protect
against, we never switched to it (even though I implemented it
specifically to harden container runtimes).
Unfortunately, It turns out that mount *sources* are a threat we didn't
fully consider. Since TIOCGPTPEER already solves this problem entirely
for us in a race free way, we should just use that. In a later patch, we
will add some hardening for /dev/pts/$num opening to maintain support
for very old kernels (Linux 4.13 is very old at this point, but RHEL 7
is still kicking and is stuck on Linux 3.10).
Fixes: GHSA-qw9x-cqr3-wc7r CVE-2025-52565
Reported-by: Lei Wang <ssst0n3@gmail.com> (CVE-2025-52565)
Reported-by: lfbzhm <lifubang@acmcoder.com> (CVE-2025-52565)
Reported-by: Aleksa Sarai <cyphar@cyphar.com> (TIOCGPTPEER)
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Currently, we rely on mount returning ENOTDIR when the destination is a
directory (and so mount tells us that the source is not), and fall back
to read-only tmpfs bind mount for such cases.
Theoretically, ENOTDIR can also be returned in some other cases,
resulting in the wrong type of mount being used.
Let's be more straightforward here -- call fstat on destination file
descriptor, and use the proper mount depending on whether it is a
directory.
Reported-by: Rodrigo Campos <rodrigoca@microsoft.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
When mounting a path being masked, the /dev/null might disappear from
under us, and mount (even on an opened /dev/null file descriptor) will
return ENOENT, which we deliberately ignore, as there's no need to mask
non-existent paths.
Let's open the destination path and ignore ENOENT during open, then
mount via the destination file descriptor, not ignoring ENOENT.
Reported-by: lifubang <lifubang@acmcoder.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
The /dev/null in a container should not be trusted, because when /dev
is a bind mount, /dev/null is not created by runc itself.
1. Add isDevNull which checks the fd minor/major and device type,
and verifyDevNull which does the stat and the check.
2. Rewrite maskPath to open and check /dev/null, and use its fd to
perform mounts. Move the loop over the MaskPaths into the function,
and rename it to maskPaths.
3. reOpenDevNull: use verifyDevNull and isDevNull.
4. fixStdioPermissions: use isDevNull instead of stat.
Fixes: GHSA-9493-h29p-rfm2 CVE-2025-31133
Co-authored-by: Rodrigo Campos <rodrigoca@microsoft.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
filepath-securejoin v0.3 gave us a much safer re-open primitive, we
should use it to avoid any theoretical attacks. Rather than using it
direcly, add a small pathrs wrapper to make libpathrs migrations in the
future easier...
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
We will have more wrappers around filepath-securejoin, and so move them
to their own specific package so that we can eventually use libpathrs
fairly cleanly (by swapping out the implementation).
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
This will be used for a few security patches in later patches in this
patchset. The need to verify what kind of inode we are operating on in a
race-free way turns out to be quite a common pattern...
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
Introduce and use iobail, xread, and xwrite wrappers so that we can
properly check read/write return value and call either bail or bailx on
error, with proper diagnostics (distinguishing failed read/write from a
short read/write).
This prevents the "Success" prefix in errors like:
failed to sync with stage-1: next state: Success
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Add a few missing sane_kill calls where they make sense.
Remove one useless sane_kill of stage2_pid, as during SYNC_USERMAP stage2
is not yet started. It is harmless yet it makes the code slightly harder
to read.
Set the child pid to -1 upon receiving SYNC_CHILD_FINISH
to minimize the chances of killing an unrelated process.
When a child sends SYNC_CHILD_FINISH it is about to exit
(although theoretically it could be stuck during debug logging).
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
We use bail to report fatal errors, and bail always append %m
(aka strerror(errno)). In case an error condition did not set
errno, the log message will end up with ": Success" or an error
from a stale errno value. Either case is confusing for users.
Introduce bailx which is the same as bail except it does not
append %m, and use it where appropriate.
The naming follows libc's err(3) and errx(3).
PS we still use bail in a few cases after read or write, even
if that read/write did not return an error, because the code
does not distinguish between short read/write and error (-1).
This will be addressed by the next commit.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Since sane_kill after a failed read or write, but before reporting the
error from that read or write, it may change the errno value in case
kill(2) fails.
Save and restore the errno around the call to kill.
While at it,
- change the code to return early;
- don't return kill return value as no one is using it, and the errno
value no longer correlates.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
The commit mentioned below has missed these changes.
Fixes: 17570625 ("Use for range over integers")
Signed-off-by: Ariel Otilibili <otilibil@eurecom.fr>
This is mostly to improve readability. While at it, make the script more
robust by adding -e option to shell. The exception is echo $pid which is
opportunistic and may fail depending on the order of pids in the file.
Also, remove the empty comment and a shellcheck annotation.
Fixes: c91fe9ae
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
The "runc delete --force [paused container]" test case does not check
runc pause exit code, and if added, the test fails in rootless tests,
because:
- not all rootless tests have access to cgroups;
- rootless containers doesn't have default cgroups path.
To fix, add:
- setup for rootless case;
- require cgroups_freezer;
- runc pause exit code check.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
In our bats tests, runc itself is a wrapper which calls bats run helper,
so using "run runc" is wrong as it results in calling run helper twice.
Fixes: 8d180e965
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Commands that are not run via "run" helper (cat, mkdir, __runc)
do not set $status, so it makes no sense to check it.
Fixes: 94505a04, ed548376
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
This is a bit opinionated, but some comments in integration tests do not
really help to understand the nature of the tests being performed by
stating something very obvious, like
# run busybox detached
runc run -d busybox
To make things worse, these not-so-helpful messages are being
copy/pasted over and over, and that is the main reason to remove them.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
1. Remove the devicemapper driver mentions, and is it no longer
supported by docker (or podman).
2. Remove the test example -- we have plenty of real ones.
3. Add a link to (well written and extensive) bats documentation.
4. Fix capitalization in a sentence.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Bump bats to the version from Fedora 42 (used in "fedora" job), so we
have the same version everywhere.
This also fixes an issue introduced by commit d31e6b87 (which forgot to
bump bats in GHA CI), and adds a note to the yaml in order to avoid the
same issue in the future.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
All the new code appears in main (not in the release branches),
and we only want extra linter rules to apply to new code.
Disable lint-extra job if the PR is not to the main branch.
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Aleksa Sarai