If "hidepid=4" mount option is set then do not instantiate pids that
we can not ptrace. "hidepid=4" means that procfs should only contain
pids that the caller can ptrace.

Cc: Kees Cook keescook@chromium.org
Cc: Andy Lutomirski luto@kernel.org
Signed-off-by: Djalal Harouni tixxdz@gmail.com
Signed-off-by: Alexey Gladkov gladkov.alexey@gmail.com

fs/proc/base.c | 15 +++++++++++++++
fs/proc/root.c | 14 +++++++++++---
include/linux/proc_fs.h | 1 +
3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 24b7c620ded3..49937d54e745 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c

@@ -699,6 +699,14 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,

struct task_struct *task,
int hide_pid_min)
{

-   /*
-   -   If 'hidpid' mount option is set force a ptrace check,
-   -   we indicate that we are using a filesystem syscall
-   -   by passing PTRACE_MODE_READ_FSCREDS
-   */
-   if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE)
-         return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);


-   if (proc_fs_hide_pid(fs_info) < hide_pid_min)
    return true;
    if (in_group_p(proc_fs_pid_gid(fs_info)))
    @@ -3271,7 +3279,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
    if (!task)
    goto out;

-   /* Limit procfs to only ptracable tasks */
-   if (proc_fs_hide_pid(fs_info) == HIDEPID_NOT_PTRACABLE) {
-         if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))


-         	goto out_put_task;


-   }
-   result = proc_pid_instantiate(dentry, task, NULL);
    +out_put_task:
    put_task_struct(task);
    out:
    return result;
    diff --git a/fs/proc/root.c b/fs/proc/root.c
    index e2bb015da1a8..5e27bb31f125 100644
    --- a/fs/proc/root.c
    +++ b/fs/proc/root.c
    @@ -52,6 +52,15 @@ static const struct fs_parameter_description proc_fs_parameters = {
    .specs = proc_param_specs,
    };

    +static inline int
    +valid_hidepid(unsigned int value)
    +{

-   return (value == HIDEPID_OFF ||
-         value == HIDEPID_NO_ACCESS ||


-         value == HIDEPID_INVISIBLE ||


-         value == HIDEPID_NOT_PTRACABLE);



+}
+
static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
struct proc_fs_context *ctx = fc->fs_private;

@@ -68,10 +77,9 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)

break;

case Opt_hidepid:

-         if (!valid_hidepid(result.uint_32))


-         	return invalf(fc, "proc: unknown value of hidepid.\\n");
          ctx->hidepid = result.uint_32;



-         if (ctx->hidepid < HIDEPID_OFF ||


-             ctx->hidepid > HIDEPID_INVISIBLE)


-         	return invalf(fc, "proc: hidepid value must be between 0 and 2.\\n");
          break;



default:

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index f307940f8311..6822548405a7 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h

@@ -17,6 +17,7 @@ enum {

HIDEPID_OFF = 0,
HIDEPID_NO_ACCESS = 1,
HIDEPID_INVISIBLE = 2,

-   HIDEPID_NOT_PTRACABLE = 4, /* Limit pids to only ptracable pids */