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    Subject[PATCH 7/7] vfs: show unreachable paths in getcwd and proc
    From: Miklos Szeredi <mszeredi@suse.cz>

    Prepend "(unreachable)" to path strings if the path is not reachable
    from the current root.

    Two places updated are
    - the return string from getcwd()
    - and symlinks under /proc/$PID.

    Other uses of d_path() are left unchanged (we know that some old
    software crashes if /proc/mounts is changed).

    Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
    ---
    fs/dcache.c | 54 +++++++++++++++++++++++++++++++++++++++++++++----
    fs/proc/base.c | 2 -
    include/linux/dcache.h | 1
    include/linux/path.h | 5 ++++
    4 files changed, 57 insertions(+), 5 deletions(-)

    Index: linux-2.6/fs/dcache.c
    ===================================================================
    --- linux-2.6.orig/fs/dcache.c 2010-07-06 18:08:19.000000000 +0200
    +++ linux-2.6/fs/dcache.c 2010-07-06 18:08:22.000000000 +0200
    @@ -2017,6 +2017,11 @@ static int path_with_deleted(const struc
    return prepend_path(path, root, buf, buflen);
    }

    +static int prepend_unreachable(char **buffer, int *buflen)
    +{
    + return prepend(buffer, buflen, "(unreachable)", 13);
    +}
    +
    /**
    * d_path - return the path of a dentry
    * @path: path to report
    @@ -2062,6 +2067,39 @@ char *d_path(const struct path *path, ch
    }
    EXPORT_SYMBOL(d_path);

    +/**
    + * d_path_with_unreachable - return the path of a dentry
    + * @path: path to report
    + * @buf: buffer to return value in
    + * @buflen: buffer length
    + *
    + * The difference from d_path() is that this prepends "(unreachable)"
    + * to paths which are unreachable from the current process' root.
    + */
    +char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
    +{
    + char *res = buf + buflen;
    + struct path root;
    + struct path tmp;
    + int error;
    +
    + if (path->dentry->d_op && path->dentry->d_op->d_dname)
    + return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
    +
    + get_fs_root(current->fs, &root);
    + spin_lock(&dcache_lock);
    + tmp = root;
    + error = path_with_deleted(path, &tmp, &res, &buflen);
    + if (!error && !path_equal(&tmp, &root))
    + error = prepend_unreachable(&res, &buflen);
    + spin_unlock(&dcache_lock);
    + path_put(&root);
    + if (error)
    + res = ERR_PTR(error);
    +
    + return res;
    +}
    +
    /*
    * Helper function for dentry_operations.d_dname() members
    */
    @@ -2154,15 +2192,23 @@ SYSCALL_DEFINE2(getcwd, char __user *, b
    if (!d_unlinked(pwd.dentry)) {
    unsigned long len;
    struct path tmp = root;
    - char * cwd;
    + char *cwd = page + PAGE_SIZE;
    + int buflen = PAGE_SIZE;

    - cwd = __d_path(&pwd, &tmp, page, PAGE_SIZE);
    + prepend(&cwd, &buflen, "\0", 1);
    + error = prepend_path(&pwd, &tmp, &cwd, &buflen);
    spin_unlock(&dcache_lock);

    - error = PTR_ERR(cwd);
    - if (IS_ERR(cwd))
    + if (error)
    goto out;

    + /* Unreachable from current root */
    + if (!path_equal(&tmp, &root)) {
    + error = prepend_unreachable(&cwd, &buflen);
    + if (error)
    + goto out;
    + }
    +
    error = -ERANGE;
    len = PAGE_SIZE + page - cwd;
    if (len <= size) {
    Index: linux-2.6/include/linux/dcache.h
    ===================================================================
    --- linux-2.6.orig/include/linux/dcache.h 2010-07-06 17:59:04.000000000 +0200
    +++ linux-2.6/include/linux/dcache.h 2010-07-06 18:08:22.000000000 +0200
    @@ -315,6 +315,7 @@ extern char *dynamic_dname(struct dentry

    extern char *__d_path(const struct path *path, struct path *root, char *, int);
    extern char *d_path(const struct path *, char *, int);
    +extern char *d_path_with_unreachable(const struct path *, char *, int);
    extern char *dentry_path(struct dentry *, char *, int);

    /* Allocation counts.. */
    Index: linux-2.6/fs/proc/base.c
    ===================================================================
    --- linux-2.6.orig/fs/proc/base.c 2010-07-06 18:08:06.000000000 +0200
    +++ linux-2.6/fs/proc/base.c 2010-07-06 18:08:22.000000000 +0200
    @@ -1426,7 +1426,7 @@ static int do_proc_readlink(struct path
    if (!tmp)
    return -ENOMEM;

    - pathname = d_path(path, tmp, PAGE_SIZE);
    + pathname = d_path_with_unreachable(path, tmp, PAGE_SIZE);
    len = PTR_ERR(pathname);
    if (IS_ERR(pathname))
    goto out;
    Index: linux-2.6/include/linux/path.h
    ===================================================================
    --- linux-2.6.orig/include/linux/path.h 2010-07-06 17:59:04.000000000 +0200
    +++ linux-2.6/include/linux/path.h 2010-07-06 18:08:22.000000000 +0200
    @@ -12,4 +12,9 @@ struct path {
    extern void path_get(struct path *);
    extern void path_put(struct path *);

    +static inline int path_equal(const struct path *path1, const struct path *path2)
    +{
    + return path1->mnt == path2->mnt && path1->dentry == path2->dentry;
    +}
    +
    #endif /* _LINUX_PATH_H */
    --


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