landlock: Don't lose track of restrictions on cred_transfer

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: [email protected]
Fixes: 385975dca53e ("landlock: Set up the security framework and manage credentials")
Signed-off-by: Jann Horn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mickaël Salaün <[email protected]>

0 files changed, 0 insertions, 0 deletions