6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn <jannh@xxxxxxxxxx>
commit 39705a6c29f8a2b93cf5b99528a55366c50014d1 upstream.
When a process' cred struct is replaced, this _almost_ always invokes
the cred_prepare LSM hook; but in one special case (when
KEYCTL_SESSION_TO_PARENT updates the parent's credentials), the
cred_transfer LSM hook is used instead. Landlock only implements the
cred_prepare hook, not cred_transfer, so KEYCTL_SESSION_TO_PARENT causes
all information on Landlock restrictions to be lost.
This basically means that a process with the ability to use the fork()
and keyctl() syscalls can get rid of all Landlock restrictions on
itself.
Fix it by adding a cred_transfer hook that does the same thing as the
existing cred_prepare hook. (Implemented by having hook_cred_prepare()
call hook_cred_transfer() so that the two functions are less likely to
accidentally diverge in the future.)
Cc: stable@xxxxxxxxxx
Fixes: 385975dca53e ("landlock: Set up the security framework and manage credentials")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240724-landlock-houdini-fix-v1-1-df89a4560ca3@xxxxxxxxxx
Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
security/landlock/cred.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
--- a/security/landlock/cred.c
+++ b/security/landlock/cred.c
@@ -14,8 +14,8 @@
#include "ruleset.h"
#include "setup.h"
-static int hook_cred_prepare(struct cred *const new,
- const struct cred *const old, const gfp_t gfp)
+static void hook_cred_transfer(struct cred *const new,
+ const struct cred *const old)
{
struct landlock_ruleset *const old_dom = landlock_cred(old)->domain;
@@ -23,6 +23,12 @@ static int hook_cred_prepare(struct cred
landlock_get_ruleset(old_dom);
landlock_cred(new)->domain = old_dom;
}
+}
+
+static int hook_cred_prepare(struct cred *const new,
+ const struct cred *const old, const gfp_t gfp)
+{
+ hook_cred_transfer(new, old);
return 0;
}
@@ -36,6 +42,7 @@ static void hook_cred_free(struct cred *
static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(cred_prepare, hook_cred_prepare),
+ LSM_HOOK_INIT(cred_transfer, hook_cred_transfer),
LSM_HOOK_INIT(cred_free, hook_cred_free),
};
