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Date: Mon, 5 Jan 2009 20:08:50 +1100 (EST)
From: James Morris <jmorris@...ei.org>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org,
Kentaro Takeda <takedakn@...data.co.jp>,
Toshiharu Harada <haradats@...data.co.jp>
Subject: Re: [TOMOYO #14 (mmotm 2008-12-30-16-05) 03/10] Introduce
d_realpath().
On Thu, 1 Jan 2009, Tetsuo Handa wrote:
> To remove factors that make pathname based access control difficult
> (e.g. symbolic links, "..", "//", chroot() etc.), a variant of d_path()
> which traverses up to the root of the namespace is needed.
>
> This patch introduces d_realpath(), a variant of d_path().
> While d_path() stops traversing at current->fs->root,
> d_realpath() doesn't stop traversiong at current->fs->root.
>
> Three differences compared to d_path().
> (1) Ignores current process's root directory.
> (2) Trailing '/' is added if the pathname refers to a directory.
> (3) /proc/PID/ is represented as /proc/self/ if PID equals current->tgid.
>
This needs an ack from Al and/or Christoph.
> Signed-off-by: Kentaro Takeda <takedakn@...data.co.jp>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Signed-off-by: Toshiharu Harada <haradats@...data.co.jp>
> ---
> fs/dcache.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/dcache.h | 1
> 2 files changed, 85 insertions(+)
>
> --- linux-2.6.28-mm1.orig/fs/dcache.c
> +++ linux-2.6.28-mm1/fs/dcache.c
> @@ -32,6 +32,7 @@
> #include <linux/seqlock.h>
> #include <linux/swap.h>
> #include <linux/bootmem.h>
> +#include <linux/magic.h>
> #include "internal.h"
>
>
> @@ -1978,6 +1979,89 @@ Elong:
> }
>
> /**
> + * d_realpath - Get the realpath of a dentry.
> + *
> + * @path: Pointer to "struct path".
> + * @buffer: Pointer to buffer to return value in.
> + * @buflen: Sizeof @buffer.
> + *
> + * Returns pointer to the realpath on success, an error code othersize.
> + *
> + * If @dentry is a directory, trailing '/' is appended.
> + * /proc/PID/ is replaced by /proc/self/ if PID == task_tgid_nr_ns(current).
> + */
> +char *d_realpath(struct path *path, char *buffer, int buflen)
> +{
> + struct dentry *dentry = path->dentry;
> + struct vfsmount *vfsmnt = path->mnt;
> + char *end = buffer + buflen;
> +
> + spin_lock(&dcache_lock);
> + spin_lock(&vfsmount_lock);
> + if (buflen < 1 || prepend(&end, &buflen, "", 1))
> + goto Elong;
> + /*
> + * Exception: Add trailing '/' for directory.
> + */
> + if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode) &&
> + prepend(&end, &buflen, "/", 1))
> + goto Elong;
> + for (;;) {
> + struct dentry *parent;
> + const char *name;
> + int name_len;
> + unsigned long pid;
> +
> + if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
> + /* Global root? */
> + if (vfsmnt->mnt_parent == vfsmnt)
> + break;
> + dentry = vfsmnt->mnt_mountpoint;
> + vfsmnt = vfsmnt->mnt_parent;
> + continue;
> + }
> + parent = dentry->d_parent;
> + prefetch(parent);
> + /*
> + * Exception: Use /proc/self/ rather than /proc/\$/
> + * for current process.
> + */
> + name = dentry->d_name.name;
> + name_len = dentry->d_name.len;
> + if (IS_ROOT(parent) &&
> + parent->d_sb->s_magic == PROC_SUPER_MAGIC &&
> + !strict_strtoul(name, 10, &pid)) {
> + const pid_t tgid
> + = task_tgid_nr_ns(current,
> + dentry->d_sb->s_fs_info);
> + if (tgid && (pid_t) pid == tgid) {
> + name = "self";
> + name_len = 4;
> + }
> + }
> + if (prepend(&end, &buflen, name, name_len))
> + goto Elong;
> + if (prepend(&end, &buflen, "/", 1))
> + goto Elong;
> + dentry = parent;
> + }
> + if (*end == '/') {
> + /* hit the slash */
> + buflen++;
> + end++;
> + }
> + if (prepend_name(&end, &buflen, &dentry->d_name))
> + goto Elong;
> + out:
> + spin_unlock(&vfsmount_lock);
> + spin_unlock(&dcache_lock);
> + return end;
> + Elong:
> + end = ERR_PTR(-ENAMETOOLONG);
> + goto out;
> +}
> +
> +/**
> * d_path - return the path of a dentry
> * @path: path to report
> * @buf: buffer to return value in
> --- linux-2.6.28-mm1.orig/include/linux/dcache.h
> +++ linux-2.6.28-mm1/include/linux/dcache.h
> @@ -305,6 +305,7 @@ 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 *dentry_path(struct dentry *, char *, int);
> +extern char *d_realpath(struct path *, char *, int);
>
> /* Allocation counts.. */
>
>
> --
> --
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>
--
James Morris
<jmorris@...ei.org>
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