ptrace: Remove maxargs from task_current_syscall()

task_current_syscall() has a single user that passes in 6 for maxargs, which
is the maximum arguments that can be used to get system calls from
syscall_get_arguments(). Instead of passing in a number of arguments to
grab, just get 6 arguments. The args argument even specifies that it's an
array of 6 items.

This will also allow changing syscall_get_arguments() to not get a variable
number of arguments, but always grab 6.

Linus also suggested not passing in a bunch of arguments to
task_current_syscall() but to instead pass in a pointer to a structure, and
just fill the structure. struct seccomp_data has almost all the parameters
that is needed except for the stack pointer (sp). As seccomp_data is part of
uapi, and I'm afraid to change it, a new structure was created
"syscall_info", which includes seccomp_data and adds the "sp" field.

Link: http://lkml.kernel.org/r/20161107213233.466776454@goodmis.org

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 9 insertions, 8 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ddef482f1334..6a803a0b75df 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -616,24 +616,25 @@ static int proc_pid_limits(struct seq_file *m, struct pid_namespace *ns,
 static int proc_pid_syscall(struct seq_file *m, struct pid_namespace *ns,
                             struct pid *pid, struct task_struct *task)
 {
-        long nr;
-        unsigned long args[6], sp, pc;
+        struct syscall_info info;
+        u64 *args = &info.data.args[0];
         int res;
 
         res = lock_trace(task);
         if (res)
                 return res;
 
-        if (task_current_syscall(task, &nr, args, 6, &sp, &pc))
+        if (task_current_syscall(task, &info))
                 seq_puts(m, "running\n");
-        else if (nr < 0)
-                seq_printf(m, "%ld 0x%lx 0x%lx\n", nr, sp, pc);
+        else if (info.data.nr < 0)
+                seq_printf(m, "%d 0x%llx 0x%llx\n",
+                           info.data.nr, info.sp, info.data.instruction_pointer);
         else
                 seq_printf(m,
-                       "%ld 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx\n",
-                       nr,
+                       "%d 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx 0x%llx\n",
+                       info.data.nr,
                        args[0], args[1], args[2], args[3], args[4], args[5],
-                       sp, pc);
+                       info.sp, info.data.instruction_pointer);
         unlock_trace(task);
 
         return 0;