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    SubjectRe: [PATCH 2/2] vfs: show unreachable paths in getcwd and proc
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    Hi Al,

    Could you please consider these patches for 2.6.36?

    Thanks,
    Miklos


    On Fri, 04 Jun 2010, Miklos Szeredi wrote:
    > 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 | 82 +++++++++++++++++++++++++++++++++++++++++--------
    > fs/proc/base.c | 2 -
    > include/linux/dcache.h | 1
    > 3 files changed, 72 insertions(+), 13 deletions(-)
    >
    > Index: linux-2.6/fs/dcache.c
    > ===================================================================
    > --- linux-2.6.orig/fs/dcache.c 2010-05-27 12:22:21.000000000 +0200
    > +++ linux-2.6/fs/dcache.c 2010-05-27 12:22:24.000000000 +0200
    > @@ -1957,6 +1957,33 @@ int __d_path(const struct path *path, st
    > return error;
    > }
    >
    > +static void current_root(struct path *root)
    > +{
    > + read_lock(&current->fs->lock);
    > + *root = current->fs->root;
    > + path_get(root);
    > + read_unlock(&current->fs->lock);
    > +}
    > +
    > +static int __d_path_with_deleted(const struct path *path, struct path *root,
    > + char **buffer, int *buflen)
    > +{
    > + int error;
    > +
    > + prepend(buffer, buflen, "\0", 1);
    > + if (d_unlinked(path->dentry)) {
    > + error = prepend(buffer, buflen, " (deleted)", 10);
    > + if (error)
    > + return error;
    > + }
    > + return __d_path(path, root, buffer, 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
    > @@ -1990,27 +2017,51 @@ char *d_path(const struct path *path, ch
    > if (path->dentry->d_op && path->dentry->d_op->d_dname)
    > return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
    >
    > - read_lock(&current->fs->lock);
    > - root = current->fs->root;
    > - path_get(&root);
    > - read_unlock(&current->fs->lock);
    > + current_root(&root);
    > spin_lock(&dcache_lock);
    > ptr = buf + buflen;
    > - prepend(&ptr, &buflen, "\0", 1);
    > - if (d_unlinked(path->dentry)) {
    > - error = prepend(&ptr, &buflen, " (deleted)", 10);
    > - if (error)
    > - goto out;
    > - }
    > tmp = root;
    > - error = __d_path(path, &tmp, &ptr, &buflen);
    > -out:
    > + error = __d_path_with_deleted(path, &tmp, &ptr, &buflen);
    > spin_unlock(&dcache_lock);
    > path_put(&root);
    > return error ? ERR_PTR(error) : ptr;
    > }
    > 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 *ptr;
    > + 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);
    > +
    > + current_root(&root);
    > + spin_lock(&dcache_lock);
    > + ptr = buf + buflen;
    > + tmp = root;
    > + error = __d_path_with_deleted(path, &tmp, &ptr, &buflen);
    > + if (!error) {
    > + if (tmp.dentry != root.dentry || tmp.mnt != root.mnt)
    > + error = prepend_unreachable(&ptr, &buflen);
    > + }
    > +
    > + spin_unlock(&dcache_lock);
    > + path_put(&root);
    > + return error ? ERR_PTR(error) : ptr;
    > +}
    > +
    > /*
    > * Helper function for dentry_operations.d_dname() members
    > */
    > @@ -2118,6 +2169,13 @@ SYSCALL_DEFINE2(getcwd, char __user *, b
    > if (error)
    > goto out;
    >
    > + /* Unreachable from current root */
    > + if (tmp.dentry != root.dentry || tmp.mnt != root.mnt) {
    > + 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 2010-05-27 12:13:48.000000000 +0200
    > +++ linux-2.6/include/linux/dcache.h 2010-05-27 12:22:24.000000000 +0200
    > @@ -315,6 +315,7 @@ extern char *dynamic_dname(struct dentry
    >
    > extern int __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 2010-05-27 11:53:55.000000000 +0200
    > +++ linux-2.6/fs/proc/base.c 2010-05-27 12:22:24.000000000 +0200
    > @@ -1438,7 +1438,7 @@ 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;
    >


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