From: Jann Horn Date: Thu, 4 Jul 2019 18:44:44 +0000 (+0200) Subject: Smack: Don't ignore other bprm->unsafe flags if LSM_UNSAFE_PTRACE is set X-Git-Tag: v3.16.79~51 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eadea2cb3bae0dd512f1e2f5e5787560ac12e3fd;p=thirdparty%2Fkernel%2Fstable.git Smack: Don't ignore other bprm->unsafe flags if LSM_UNSAFE_PTRACE is set 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(). Fixes: 5663884caab1 ("Smack: unify all ptrace accesses in the smack") Signed-off-by: Jann Horn Signed-off-by: Casey Schaufler [bwh: Backported to 3.16: Ignore LSM_UNSAFE_PTRACE_CAP, which is also handled by the preceding if-statement.] Signed-off-by: Ben Hutchings --- diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c index a6a3482e4d7e8..6392a6d933acc 100644 --- a/security/smack/smack_lsm.c +++ b/security/smack/smack_lsm.c @@ -553,7 +553,8 @@ 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 | LSM_UNSAFE_PTRACE_CAP)) return -EPERM; bsp->smk_task = isp->smk_task;