Re: [12/24] proc: Add fs_context support to procfs [ver #7]

From: Andrei Vagin
Date: Mon Jun 18 2018 - 23:35:31 EST

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Hi David,

We run CRIU tests for vfs/for-next, and today a few of these test failed. I
found that the problem appears after this patch..

https://travis-ci.org/avagin/linux/jobs/393766778

The reproducer is attached. It creates a process in a new set of namespaces
(user, mount, etc) and then this process fails to mount procfs, the mount
syscall returns EBUSY.

666 pipe([3, 4]) = 0
666 clone(child_stack=0x7ffc23a89400, flags=CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER|CLONE_NEWPID|CLONE_NEWNET|SIGCHLD) = 667
666 openat(AT_FDCWD, "/proc/667/uid_map", O_WRONLY <unfinished ...>
667 close(4 <unfinished ...>
666 <... openat resumed> ) = 5
666 write(5, "0 100000 100000\n100000 200000 50"..., 36 <unfinished ...>
667 <... close resumed> ) = 0
666 <... write resumed> ) = 36
666 close(5 <unfinished ...>
667 read(3, <unfinished ...>
666 <... close resumed> ) = 0
666 openat(AT_FDCWD, "/proc/667/gid_map", O_WRONLY) = 5
666 write(5, "0 400000 50000\n50000 500000 1000"..., 35) = 35
666 close(5) = 0
666 write(4, " \225\250#", 4) = 4
667 <... read resumed> " \225\250#", 4) = 4
666 wait4(667, <unfinished ...>
667 setsid() = 1
667 setuid(0) = 0
667 setgid(0) = 0
667 setgroups(0, NULL) = 0
667 mount("proc", "/mnt", "proc", MS_MGC_VAL|MS_NOSUID|MS_NODEV|MS_NOEXEC, NULL) = -1 EBUSY (Device or resource busy)

Thanks,
Andrei

On Thu, Apr 19, 2018 at 02:32:28PM +0100, David Howells wrote:
> Add fs_context support to procfs.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> ---
>
> fs/proc/inode.c | 2 -
> fs/proc/internal.h | 2 -
> fs/proc/root.c | 169 ++++++++++++++++++++++++++++++++++------------------
> 3 files changed, 113 insertions(+), 60 deletions(-)
>
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> index 0b13cf6eb6d7..7aa86dd65ba8 100644
> --- a/fs/proc/inode.c
> +++ b/fs/proc/inode.c
> @@ -128,7 +128,7 @@ const struct super_operations proc_sops = {
> .drop_inode = generic_delete_inode,
> .evict_inode = proc_evict_inode,
> .statfs = simple_statfs,
> - .remount_fs = proc_remount,
> + .reconfigure = proc_reconfigure,
> .show_options = proc_show_options,
> };
>
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index 3182e1b636d3..a5ab9504768a 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -254,7 +254,7 @@ static inline void proc_tty_init(void) {}
> extern struct proc_dir_entry proc_root;
>
> extern void proc_self_init(void);
> -extern int proc_remount(struct super_block *, int *, char *, size_t);
> +extern int proc_reconfigure(struct super_block *, struct fs_context *);
>
> /*
> * task_[no]mmu.c
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index 2fbc177f37a8..e6bd31fbc714 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -19,14 +19,24 @@
> #include <linux/module.h>
> #include <linux/bitops.h>
> #include <linux/user_namespace.h>
> +#include <linux/fs_context.h>
> #include <linux/mount.h>
> #include <linux/pid_namespace.h>
> #include <linux/parser.h>
> #include <linux/cred.h>
> #include <linux/magic.h>
> +#include <linux/slab.h>
>
> #include "internal.h"
>
> +struct proc_fs_context {
> + struct fs_context fc;
> + struct pid_namespace *pid_ns;
> + unsigned long mask;
> + int hidepid;
> + int gid;
> +};
> +
> enum {
> Opt_gid, Opt_hidepid, Opt_err,
> };
> @@ -37,56 +47,60 @@ static const match_table_t tokens = {
> {Opt_err, NULL},
> };
>
> -static int proc_parse_options(char *options, struct pid_namespace *pid)
> +static int proc_parse_option(struct fs_context *fc, char *opt, size_t len)
> {
> - char *p;
> + struct proc_fs_context *ctx = container_of(fc, struct proc_fs_context, fc);
> substring_t args[MAX_OPT_ARGS];
> - int option;
> -
> - if (!options)
> - return 1;
> -
> - while ((p = strsep(&options, ",")) != NULL) {
> - int token;
> - if (!*p)
> - continue;
> -
> - args[0].to = args[0].from = NULL;
> - token = match_token(p, tokens, args);
> - switch (token) {
> - case Opt_gid:
> - if (match_int(&args[0], &option))
> - return 0;
> - pid->pid_gid = make_kgid(current_user_ns(), option);
> - break;
> - case Opt_hidepid:
> - if (match_int(&args[0], &option))
> - return 0;
> - if (option < HIDEPID_OFF ||
> - option > HIDEPID_INVISIBLE) {
> - pr_err("proc: hidepid value must be between 0 and 2.\n");
> - return 0;
> - }
> - pid->hide_pid = option;
> - break;
> - default:
> - pr_err("proc: unrecognized mount option \"%s\" "
> - "or missing value\n", p);
> - return 0;
> + int token;
> +
> + args[0].to = args[0].from = NULL;
> + token = match_token(opt, tokens, args);
> + switch (token) {
> + case Opt_gid:
> + if (match_int(&args[0], &ctx->gid))
> + return -EINVAL;
> + break;
> +
> + case Opt_hidepid:
> + if (match_int(&args[0], &ctx->hidepid))
> + return -EINVAL;
> + if (ctx->hidepid < HIDEPID_OFF ||
> + ctx->hidepid > HIDEPID_INVISIBLE) {
> + pr_err("proc: hidepid value must be between 0 and 2.\n");
> + return -EINVAL;
> }
> + break;
> +
> + default:
> + pr_err("proc: unrecognized mount option \"%s\" or missing value\n",
> + opt);
> + return -EINVAL;
> }
>
> - return 1;
> + ctx->mask |= 1 << token;
> + return 0;
> +}
> +
> +static void proc_set_options(struct super_block *s,
> + struct fs_context *fc,
> + struct pid_namespace *pid_ns,
> + struct user_namespace *user_ns)
> +{
> + struct proc_fs_context *ctx = container_of(fc, struct proc_fs_context, fc);
> +
> + if (ctx->mask & (1 << Opt_gid))
> + pid_ns->pid_gid = make_kgid(user_ns, ctx->gid);
> + if (ctx->mask & (1 << Opt_hidepid))
> + pid_ns->hide_pid = ctx->hidepid;
> }
>
> -static int proc_fill_super(struct super_block *s, void *data, size_t data_size, int silent)
> +static int proc_fill_super(struct super_block *s, struct fs_context *fc)
> {
> - struct pid_namespace *ns = get_pid_ns(s->s_fs_info);
> + struct pid_namespace *pid_ns = get_pid_ns(s->s_fs_info);
> struct inode *root_inode;
> int ret;
>
> - if (!proc_parse_options(data, ns))
> - return -EINVAL;
> + proc_set_options(s, fc, pid_ns, current_user_ns());
>
> /* User space would break if executables or devices appear on proc */
> s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV;
> @@ -103,7 +117,7 @@ static int proc_fill_super(struct super_block *s, void *data, size_t data_size,
> * top of it
> */
> s->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
> -
> +
> pde_get(&proc_root);
> root_inode = proc_get_inode(s, &proc_root);
> if (!root_inode) {
> @@ -124,30 +138,46 @@ static int proc_fill_super(struct super_block *s, void *data, size_t data_size,
> return proc_setup_thread_self(s);
> }
>
> -int proc_remount(struct super_block *sb, int *flags,
> - char *data, size_t data_size)
> +int proc_reconfigure(struct super_block *sb, struct fs_context *fc)
> {
> struct pid_namespace *pid = sb->s_fs_info;
>
> sync_filesystem(sb);
> - return !proc_parse_options(data, pid);
> +
> + if (fc)
> + proc_set_options(sb, fc, pid, current_user_ns());
> + return 0;
> }
>
> -static struct dentry *proc_mount(struct file_system_type *fs_type,
> - int flags, const char *dev_name,
> - void *data, size_t data_size)
> +static int proc_get_tree(struct fs_context *fc)
> {
> - struct pid_namespace *ns;
> + struct proc_fs_context *ctx = container_of(fc, struct proc_fs_context, fc);
>
> - if (flags & SB_KERNMOUNT) {
> - ns = data;
> - data = NULL;
> - } else {
> - ns = task_active_pid_ns(current);
> - }
> + ctx->fc.s_fs_info = ctx->pid_ns;
> + return vfs_get_super(fc, vfs_get_keyed_super, proc_fill_super);
> +}
>
> - return mount_ns(fs_type, flags, data, data_size, ns, ns->user_ns,
> - proc_fill_super);
> +static void proc_fs_context_free(struct fs_context *fc)
> +{
> + struct proc_fs_context *ctx = container_of(fc, struct proc_fs_context, fc);
> +
> + if (ctx->pid_ns)
> + put_pid_ns(ctx->pid_ns);
> +}
> +
> +static const struct fs_context_operations proc_fs_context_ops = {
> + .free = proc_fs_context_free,
> + .parse_option = proc_parse_option,
> + .get_tree = proc_get_tree,
> +};
> +
> +static int proc_init_fs_context(struct fs_context *fc, struct super_block *src_sb)
> +{
> + struct proc_fs_context *ctx = container_of(fc, struct proc_fs_context, fc);
> +
> + ctx->pid_ns = get_pid_ns(task_active_pid_ns(current));
> + ctx->fc.ops = &proc_fs_context_ops;
> + return 0;
> }
>
> static void proc_kill_sb(struct super_block *sb)
> @@ -165,7 +195,8 @@ static void proc_kill_sb(struct super_block *sb)
>
> static struct file_system_type proc_fs_type = {
> .name = "proc",
> - .mount = proc_mount,
> + .fs_context_size = sizeof(struct proc_fs_context),
> + .init_fs_context = proc_init_fs_context,
> .kill_sb = proc_kill_sb,
> .fs_flags = FS_USERNS_MOUNT,
> };
> @@ -205,7 +236,7 @@ static struct dentry *proc_root_lookup(struct inode * dir, struct dentry * dentr
> {
> if (!proc_pid_lookup(dir, dentry, flags))
> return NULL;
> -
> +
> return proc_lookup(dir, dentry, flags);
> }
>
> @@ -259,9 +290,31 @@ struct proc_dir_entry proc_root = {
>
> int pid_ns_prepare_proc(struct pid_namespace *ns)
> {
> + struct proc_fs_context *ctx;
> + struct fs_context *fc;
> struct vfsmount *mnt;
> + int ret;
> +
> + fc = vfs_new_fs_context(&proc_fs_type, NULL, 0,
> + FS_CONTEXT_FOR_KERNEL_MOUNT);
> + if (IS_ERR(fc))
> + return PTR_ERR(fc);
> +
> + ctx = container_of(fc, struct proc_fs_context, fc);
> + if (ctx->pid_ns != ns) {
> + put_pid_ns(ctx->pid_ns);
> + get_pid_ns(ns);
> + ctx->pid_ns = ns;
> + }
> +
> + ret = vfs_get_tree(fc);
> + if (ret < 0) {
> + put_fs_context(fc);
> + return ret;
> + }
>
> - mnt = kern_mount_data(&proc_fs_type, ns, 0);
> + mnt = vfs_create_mount(fc);
> + put_fs_context(fc);
> if (IS_ERR(mnt))
> return PTR_ERR(mnt);
>
#define _GNU_SOURCE
#include <sys/types.h>
#include <sched.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/mount.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <grp.h>
#include <linux/limits.h>

#define NS_STACK_SIZE 4096

#define __stack_aligned__ __attribute__((aligned(16)))

/* All arguments should be above stack, because it grows down */
struct ns_exec_args {
char stack[NS_STACK_SIZE] __stack_aligned__;
char stack_ptr[0];
int pfd[2];
};

static int ns_exec(void *_arg)
{
struct ns_exec_args *args = (struct ns_exec_args *) _arg;
int ret;

close(args->pfd[1]);
if (read(args->pfd[0], &ret, sizeof(ret)) != sizeof(ret))
return -1;

setsid();

if (setuid(0) || setgid(0) || setgroups(0, NULL)) {
fprintf(stderr, "set*id failed: %m\n");
return -1;
}

if (mount("proc", "/mnt", "proc", MS_MGC_VAL | MS_NOSUID | MS_NOEXEC | MS_NODEV, NULL)) {
fprintf(stderr, "mount(/proc) failed: %m\n");
return -1;
}

return 0;
}

#define UID_MAP "0 100000 100000\n100000 200000 50000"
#define GID_MAP "0 400000 50000\n50000 500000 100000"
int main()
{
pid_t pid;
int ret, status;
struct ns_exec_args args;
int flags;
char pname[PATH_MAX];
int fd, pfd[2];

if (pipe(pfd))
return 1;

args.pfd[0] = pfd[0];
args.pfd[1] = pfd[1];

flags = CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWUTS |
CLONE_NEWNET | CLONE_NEWIPC | CLONE_NEWUSER | SIGCHLD;

pid = clone(ns_exec, args.stack_ptr, flags, &args);
if (pid < 0) {
fprintf(stderr, "clone() failed: %m\n");
exit(1);
}

snprintf(pname, sizeof(pname), "/proc/%d/uid_map", pid);
fd = open(pname, O_WRONLY);
if (fd < 0) {
fprintf(stderr, "open(%s): %m\n", pname);
exit(1);
}
if (write(fd, UID_MAP, sizeof(UID_MAP)) < 0) {
fprintf(stderr, "write(" UID_MAP "): %m\n");
exit(1);
}
close(fd);

snprintf(pname, sizeof(pname), "/proc/%d/gid_map", pid);
fd = open(pname, O_WRONLY);
if (fd < 0) {
fprintf(stderr, "open(%s): %m\n", pname);
exit(1);
}
if (write(fd, GID_MAP, sizeof(GID_MAP)) < 0) {
fprintf(stderr, "write(" GID_MAP "): %m\n");
exit(1);
}
close(fd);

if (write(pfd[1], &ret, sizeof(ret)) != sizeof(ret))
return 1;

if (waitpid(pid, &status, 0) != pid)
return 1;
if (status)
return 1;

return 0;
}

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