ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE

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>

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index eea2650..ccc4b46 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -371,6 +371,26 @@ bool ptrace_may_access(struct task_struct *task, unsigned int mode)
        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_struct *task, long request,
        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 *tsk, char __user *src, unsigned long ds
 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;