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    Subject[PATCH v10 4/9] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option
    Date
    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>
    Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
    Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
    ---
    fs/proc/base.c | 15 +++++++++++++++
    fs/proc/root.c | 13 ++++++++++---
    include/linux/proc_fs.h | 1 +
    3 files changed, 26 insertions(+), 3 deletions(-)

    diff --git a/fs/proc/base.c b/fs/proc/base.c
    index 43a28907baf9..1ebe9eba48ea 100644
    --- a/fs/proc/base.c
    +++ b/fs/proc/base.c
    @@ -701,6 +701,14 @@ 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 (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE)
    + return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
    +
    if (fs_info->hide_pid < hide_pid_min)
    return true;
    if (in_group_p(fs_info->pid_gid))
    @@ -3319,7 +3327,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
    if (!task)
    goto out;

    + /* Limit procfs to only ptraceable tasks */
    + if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE) {
    + 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 616e8976185c..62eae22403d2 100644
    --- a/fs/proc/root.c
    +++ b/fs/proc/root.c
    @@ -47,6 +47,14 @@ static const struct fs_parameter_spec proc_fs_parameters[] = {
    {}
    };

    +static inline int valid_hidepid(unsigned int value)
    +{
    + return (value == HIDEPID_OFF ||
    + value == HIDEPID_NO_ACCESS ||
    + value == HIDEPID_INVISIBLE ||
    + value == HIDEPID_NOT_PTRACEABLE);
    +}
    +
    static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
    {
    struct proc_fs_context *ctx = fc->fs_private;
    @@ -63,10 +71,9 @@ 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 invalfc(fc, "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 7d852dbca253..21d19353fdc7 100644
    --- a/include/linux/proc_fs.h
    +++ b/include/linux/proc_fs.h
    @@ -32,6 +32,7 @@ enum {
    HIDEPID_OFF = 0,
    HIDEPID_NO_ACCESS = 1,
    HIDEPID_INVISIBLE = 2,
    + HIDEPID_NOT_PTRACEABLE = 4, /* Limit pids to only ptraceable pids */
    };

    struct proc_fs_info {
    --
    2.25.2
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