[PATCH 4.9 014/218] ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE

Greg Kroah-Hartman
2022-04-18T14:08:11Z

From: Jann Horn <jannh@google.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@kernel.org
Fixes: 13c4a90119d2 ("seccomp: add ptrace options for suspend/resume")
Signed-off-by: Jann Horn <jannh@google.com>
Link: https://lkml.kernel.org/r/20220319010838.1386861-1-jannh@google.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;
@@ -656,22 +684,11 @@ 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;