From: Jann Horn jannh@google.com
commit 3675f052b43ba51b99b85b073c7070e083f3e6fb upstream.
There is a logic bug in the current smack_bprm_set_creds(): If LSM_UNSAFE_PTRACE is set, but the ptrace state is deemed to be acceptable (e.g. because the ptracer detached in the meantime), the other ->unsafe flags aren't checked. As far as I can tell, this means that something like the following could work (but I haven't tested it):
- task A: create task B with fork() - task B: set NO_NEW_PRIVS - task B: install a seccomp filter that makes open() return 0 under some conditions - task B: replace fd 0 with a malicious library - task A: attach to task B with PTRACE_ATTACH - task B: execve() a file with an SMACK64EXEC extended attribute - task A: while task B is still in the middle of execve(), exit (which destroys the ptrace relationship)
Make sure that if any flags other than LSM_UNSAFE_PTRACE are set in bprm->unsafe, we reject the execve().
Cc: stable@vger.kernel.org Fixes: 5663884caab1 ("Smack: unify all ptrace accesses in the smack") Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Casey Schaufler casey@schaufler-ca.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- security/smack/smack_lsm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -944,7 +944,8 @@ static int smack_bprm_set_creds(struct l
if (rc != 0) return rc; - } else if (bprm->unsafe) + } + if (bprm->unsafe & ~LSM_UNSAFE_PTRACE) return -EPERM;
bsp->smk_task = isp->smk_task;