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Subject[TOMOYO #11 (linux-next) 04/11] Introduce d_realpath().
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.

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.

Signed-off-by: Kentaro Takeda <takedakn@nttdata.co.jp>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Toshiharu Harada <haradats@nttdata.co.jp>
---
fs/dcache.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/dcache.h | 1
2 files changed, 80 insertions(+)

--- linux-next.orig/fs/dcache.c
+++ linux-next/fs/dcache.c
@@ -33,6 +33,7 @@
#include <linux/swap.h>
#include <linux/bootmem.h>
#include <linux/backing-dev.h>
+#include <linux/magic.h>
#include "internal.h"


@@ -1972,6 +1973,84 @@ 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.
+ * If /proc/PID/ is replaced by /proc/self/ if PID == current->tgid.
+ */
+char *d_realpath(struct path *path, char *buffer, int buflen)
+{
+ struct dentry *dentry = path->dentry;
+ struct vfsmount *vfsmnt = path->mnt;
+ char *end = buffer + buflen;
+ char self_pid[16];
+
+ snprintf(self_pid, sizeof(self_pid), "%u", current->tgid);
+ 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;
+
+ 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;
+ if (IS_ROOT(parent) &&
+ parent->d_sb->s_magic == PROC_SUPER_MAGIC &&
+ !strcmp(name, self_pid)) {
+ if (prepend(&end, &buflen, "self", 4))
+ goto Elong;
+ } else {
+ if (prepend_name(&end, &buflen, &dentry->d_name))
+ 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-next.orig/include/linux/dcache.h
+++ linux-next/include/linux/dcache.h
@@ -304,6 +304,7 @@ 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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