linux-kernel - [PATCH 5.17 0042/1126] ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE

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Message-Id: <20220405070408.793958394@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:13:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable@...nel.org,
        Jann Horn <jannh@...gle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 5.17 0042/1126] ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE

From: Jann Horn <jannh@...gle.com>

commit ee1fee900537b5d9560e9f937402de5ddc8412f3 upstream.

Setting PTRACE_O_SUSPEND_SECCOMP is supposed to be a highly privileged
operation because it allows the tracee to completely bypass all seccomp
filters on kernels with CONFIG_CHECKPOINT_RESTORE=y. It is only supposed to
be settable by a process with global CAP_SYS_ADMIN, and only if that
process is not subject to any seccomp filters at all.

However, while these permission checks were done on the PTRACE_SETOPTIONS
path, they were missing on the PTRACE_SEIZE path, which also sets
user-specified ptrace flags.

Move the permissions checks out into a helper function and let both
ptrace_attach() and ptrace_setoptions() call it.

Cc: stable@...nel.org
Fixes: 13c4a90119d2 ("seccomp: add ptrace options for suspend/resume")
Signed-off-by: Jann Horn <jannh@...gle.com>
Link: https://lkml.kernel.org/r/20220319010838.1386861-1-jannh@google.com
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/ptrace.c |   47 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 15 deletions(-)

--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -371,6 +371,26 @@ bool ptrace_may_access(struct task_struc
 	return !err;
 }
 
+static int check_ptrace_options(unsigned long data)
+{
+	if (data & ~(unsigned long)PTRACE_O_MASK)
+		return -EINVAL;
+
+	if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
+		if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
+		    !IS_ENABLED(CONFIG_SECCOMP))
+			return -EINVAL;
+
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (seccomp_mode(&current->seccomp) != SECCOMP_MODE_DISABLED ||
+		    current->ptrace & PT_SUSPEND_SECCOMP)
+			return -EPERM;
+	}
+	return 0;
+}
+
 static int ptrace_attach(struct task_struct *task, long request,
 			 unsigned long addr,
 			 unsigned long flags)
@@ -382,8 +402,16 @@ static int ptrace_attach(struct task_str
 	if (seize) {
 		if (addr != 0)
 			goto out;
+		/*
+		 * This duplicates the check in check_ptrace_options() because
+		 * ptrace_attach() and ptrace_setoptions() have historically
+		 * used different error codes for unknown ptrace options.
+		 */
 		if (flags & ~(unsigned long)PTRACE_O_MASK)
 			goto out;
+		retval = check_ptrace_options(flags);
+		if (retval)
+			return retval;
 		flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT);
 	} else {
 		flags = PT_PTRACED;
@@ -654,22 +682,11 @@ int ptrace_writedata(struct task_struct
 static int ptrace_setoptions(struct task_struct *child, unsigned long data)
 {
 	unsigned flags;
+	int ret;
 
-	if (data & ~(unsigned long)PTRACE_O_MASK)
-		return -EINVAL;
-
-	if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
-		if (!IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
-		    !IS_ENABLED(CONFIG_SECCOMP))
-			return -EINVAL;
-
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
-
-		if (seccomp_mode(&current->seccomp) != SECCOMP_MODE_DISABLED ||
-		    current->ptrace & PT_SUSPEND_SECCOMP)
-			return -EPERM;
-	}
+	ret = check_ptrace_options(data);
+	if (ret)
+		return ret;
 
 	/* Avoid intermediate state when all opts are cleared */
 	flags = child->ptrace;