linux-kernel - [PATCH 6/5] capability: Repair sidechannel test in ptrace

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Date:   Thu, 27 Sep 2018 12:17:20 -0700
From:   Casey Schaufler <casey.schaufler@...el.com>
To:     kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
        casey.schaufler@...el.com, dave.hansen@...el.com,
        deneen.t.dock@...el.com, kristen@...ux.intel.com,
        arjan@...ux.intel.com
Subject: [PATCH 6/5] capability: Repair sidechannel test in ptrace

From: Casey Schaufler <casey@...aufler-ca.com>

The PTRACE_MODE_SCHED check erroniously returns 0 in
all cases. It should be returning -EPERM. This fixes
the logic to correct that error.

Signed-off-by: Casey Schaufler <casey.schaufler@...el.com>
---
 security/commoncap.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/security/commoncap.c b/security/commoncap.c
index e77457110d05..70a7e3d19c16 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -152,9 +152,8 @@ int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
 	if (cred->user_ns == child_cred->user_ns &&
 	    cap_issubset(child_cred->cap_permitted, *caller_caps))
 		goto out;
-	if (mode & PTRACE_MODE_SCHED)
-		goto out;
-	if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
+	if (!(mode & PTRACE_MODE_SCHED) &&
+	    ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
 		goto out;
 	ret = -EPERM;
 out:
-- 
2.17.1