From 3675f052b43ba51b99b85b073c7070e083f3e6fb Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Thu, 4 Jul 2019 20:44:44 +0200 Subject: Smack: Don't ignore other bprm->unsafe flags if LSM_UNSAFE_PTRACE is set 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 Signed-off-by: Casey Schaufler --- security/smack/smack_lsm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index 4c5e5a438f8b..d8b59480a01c 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -937,7 +937,8 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm) if (rc != 0) return rc; - } else if (bprm->unsafe) + } + if (bprm->unsafe & ~LSM_UNSAFE_PTRACE) return -EPERM; bsp->smk_task = isp->smk_task; -- cgit v1.2.3