fd.c

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#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/dcache.h>
#include <linux/path.h>
#include <linux/fdtable.h>
#include <linux/namei.h>
#include <linux/pid.h>
#include <linux/security.h>
#include <linux/file.h>
#include <linux/seq_file.h>

#include <linux/proc_fs.h>

#include "internal.h"
#include "fd.h"

static int seq_show(struct seq_file *m, void *v)
{
    struct files_struct *files = NULL;
    int f_flags = 0, ret = -ENOENT;
    struct file *file = NULL;
    struct task_struct *task;

    task = get_proc_task(m->private);
    if (!task)
        return -ENOENT;

    files = get_files_struct(task);
    put_task_struct(task);

    if (files) {
        int fd = proc_fd(m->private);

        spin_lock(&files->file_lock);
        file = fcheck_files(files, fd);
        if (file) {
            struct fdtable *fdt = files_fdtable(files);

            f_flags = file->f_flags;
            if (close_on_exec(fd, fdt))
                f_flags |= O_CLOEXEC;

            get_file(file);
            ret = 0;
        }
        spin_unlock(&files->file_lock);
        put_files_struct(files);
    }

    if (!ret) {
                seq_printf(m, "pos:\t%lli\nflags:\t0%o\n",
               (long long)file->f_pos, f_flags);
        fput(file);
    }

    return ret;
}

static int seq_fdinfo_open(struct inode *inode, struct file *file)
{
    return single_open(file, seq_show, inode);
}

static const struct file_operations proc_fdinfo_file_operations = {
    .open       = seq_fdinfo_open,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .release    = single_release,
};

static int tid_fd_revalidate(struct dentry *dentry, unsigned int flags)
{
    struct files_struct *files;
    struct task_struct *task;
    const struct cred *cred;
    struct inode *inode;
    int fd;

    if (flags & LOOKUP_RCU)
        return -ECHILD;

    inode = dentry->d_inode;
    task = get_proc_task(inode);
    fd = proc_fd(inode);

    if (task) {
        files = get_files_struct(task);
        if (files) {
            struct file *file;

            rcu_read_lock();
            file = fcheck_files(files, fd);
            if (file) {
                unsigned f_mode = file->f_mode;

                rcu_read_unlock();
                put_files_struct(files);

                if (task_dumpable(task)) {
                    rcu_read_lock();
                    cred = __task_cred(task);
                    inode->i_uid = cred->euid;
                    inode->i_gid = cred->egid;
                    rcu_read_unlock();
                } else {
                    inode->i_uid = GLOBAL_ROOT_UID;
                    inode->i_gid = GLOBAL_ROOT_GID;
                }

                if (S_ISLNK(inode->i_mode)) {
                    unsigned i_mode = S_IFLNK;
                    if (f_mode & FMODE_READ)
                        i_mode |= S_IRUSR | S_IXUSR;
                    if (f_mode & FMODE_WRITE)
                        i_mode |= S_IWUSR | S_IXUSR;
                    inode->i_mode = i_mode;
                }

                security_task_to_inode(task, inode);
                put_task_struct(task);
                return 1;
            }
            rcu_read_unlock();
            put_files_struct(files);
        }
        put_task_struct(task);
    }

    d_drop(dentry);
    return 0;
}

static const struct dentry_operations tid_fd_dentry_operations = {
    .d_revalidate   = tid_fd_revalidate,
    .d_delete   = pid_delete_dentry,
};

static int proc_fd_link(struct dentry *dentry, struct path *path)
{
    struct files_struct *files = NULL;
    struct task_struct *task;
    int ret = -ENOENT;

    task = get_proc_task(dentry->d_inode);
    if (task) {
        files = get_files_struct(task);
        put_task_struct(task);
    }

    if (files) {
        int fd = proc_fd(dentry->d_inode);
        struct file *fd_file;

        spin_lock(&files->file_lock);
        fd_file = fcheck_files(files, fd);
        if (fd_file) {
            *path = fd_file->f_path;
            path_get(&fd_file->f_path);
            ret = 0;
        }
        spin_unlock(&files->file_lock);
        put_files_struct(files);
    }

    return ret;
}

static struct dentry *
proc_fd_instantiate(struct inode *dir, struct dentry *dentry,
            struct task_struct *task, const void *ptr)
{
    struct dentry *error = ERR_PTR(-ENOENT);
    unsigned fd = (unsigned long)ptr;
    struct proc_inode *ei;
    struct inode *inode;

    inode = proc_pid_make_inode(dir->i_sb, task);
    if (!inode)
        goto out;

    ei = PROC_I(inode);
    ei->fd = fd;

    inode->i_mode = S_IFLNK;
    inode->i_op = &proc_pid_link_inode_operations;
    inode->i_size = 64;

    ei->op.proc_get_link = proc_fd_link;

    d_set_d_op(dentry, &tid_fd_dentry_operations);
    d_add(dentry, inode);

    /* Close the race of the process dying before we return the dentry */
    if (tid_fd_revalidate(dentry, 0))
        error = NULL;
 out:
    return error;
}

static struct dentry *proc_lookupfd_common(struct inode *dir,
                       struct dentry *dentry,
                       instantiate_t instantiate)
{
    struct task_struct *task = get_proc_task(dir);
    struct dentry *result = ERR_PTR(-ENOENT);
    unsigned fd = name_to_int(dentry);

    if (!task)
        goto out_no_task;
    if (fd == ~0U)
        goto out;

    result = instantiate(dir, dentry, task, (void *)(unsigned long)fd);
out:
    put_task_struct(task);
out_no_task:
    return result;
}

static int proc_readfd_common(struct file * filp, void * dirent,
                  filldir_t filldir, instantiate_t instantiate)
{
    struct dentry *dentry = filp->f_path.dentry;
    struct inode *inode = dentry->d_inode;
    struct task_struct *p = get_proc_task(inode);
    struct files_struct *files;
    unsigned int fd, ino;
    int retval;

    retval = -ENOENT;
    if (!p)
        goto out_no_task;
    retval = 0;

    fd = filp->f_pos;
    switch (fd) {
        case 0:
            if (filldir(dirent, ".", 1, 0, inode->i_ino, DT_DIR) < 0)
                goto out;
            filp->f_pos++;
        case 1:
            ino = parent_ino(dentry);
            if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0)
                goto out;
            filp->f_pos++;
        default:
            files = get_files_struct(p);
            if (!files)
                goto out;
            rcu_read_lock();
            for (fd = filp->f_pos - 2;
                 fd < files_fdtable(files)->max_fds;
                 fd++, filp->f_pos++) {
                char name[PROC_NUMBUF];
                int len;
                int rv;

                if (!fcheck_files(files, fd))
                    continue;
                rcu_read_unlock();

                len = snprintf(name, sizeof(name), "%d", fd);
                rv = proc_fill_cache(filp, dirent, filldir,
                             name, len, instantiate, p,
                             (void *)(unsigned long)fd);
                if (rv < 0)
                    goto out_fd_loop;
                rcu_read_lock();
            }
            rcu_read_unlock();
out_fd_loop:
            put_files_struct(files);
    }
out:
    put_task_struct(p);
out_no_task:
    return retval;
}

static int proc_readfd(struct file *filp, void *dirent, filldir_t filldir)
{
    return proc_readfd_common(filp, dirent, filldir, proc_fd_instantiate);
}

const struct file_operations proc_fd_operations = {
    .read       = generic_read_dir,
    .readdir    = proc_readfd,
    .llseek     = default_llseek,
};

static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
                    unsigned int flags)
{
    return proc_lookupfd_common(dir, dentry, proc_fd_instantiate);
}

/*
 * /proc/pid/fd needs a special permission handler so that a process can still
 * access /proc/self/fd after it has executed a setuid().
 */
int proc_fd_permission(struct inode *inode, int mask)
{
    int rv = generic_permission(inode, mask);
    if (rv == 0)
        return 0;
    if (task_pid(current) == proc_pid(inode))
        rv = 0;
    return rv;
}

const struct inode_operations proc_fd_inode_operations = {
    .lookup     = proc_lookupfd,
    .permission = proc_fd_permission,
    .setattr    = proc_setattr,
};

static struct dentry *
proc_fdinfo_instantiate(struct inode *dir, struct dentry *dentry,
            struct task_struct *task, const void *ptr)
{
    struct dentry *error = ERR_PTR(-ENOENT);
    unsigned fd = (unsigned long)ptr;
    struct proc_inode *ei;
    struct inode *inode;

    inode = proc_pid_make_inode(dir->i_sb, task);
    if (!inode)
        goto out;

    ei = PROC_I(inode);
    ei->fd = fd;

    inode->i_mode = S_IFREG | S_IRUSR;
    inode->i_fop = &proc_fdinfo_file_operations;

    d_set_d_op(dentry, &tid_fd_dentry_operations);
    d_add(dentry, inode);

    /* Close the race of the process dying before we return the dentry */
    if (tid_fd_revalidate(dentry, 0))
        error = NULL;
 out:
    return error;
}

static struct dentry *
proc_lookupfdinfo(struct inode *dir, struct dentry *dentry, unsigned int flags)
{
    return proc_lookupfd_common(dir, dentry, proc_fdinfo_instantiate);
}

static int proc_readfdinfo(struct file *filp, void *dirent, filldir_t filldir)
{
    return proc_readfd_common(filp, dirent, filldir,
                  proc_fdinfo_instantiate);
}

const struct inode_operations proc_fdinfo_inode_operations = {
    .lookup     = proc_lookupfdinfo,
    .setattr    = proc_setattr,
};

const struct file_operations proc_fdinfo_operations = {
    .read       = generic_read_dir,
    .readdir    = proc_readfdinfo,
    .llseek     = default_llseek,
};