1 files changed, 54 insertions, 28 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index a901c6901bce..89509b5a090e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -36,6 +36,7 @@
 #include <linux/bit_spinlock.h>
 #include <linux/rculist_bl.h>
 #include <linux/prefetch.h>
+#include <linux/ratelimit.h>
 #include "internal.h"
 
 /*
@@ -2383,8 +2384,16 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)
                                 actual = __d_unalias(inode, dentry, alias);
                         }
                         write_sequnlock(&rename_lock);
-                        if (IS_ERR(actual))
+                        if (IS_ERR(actual)) {
+                                if (PTR_ERR(actual) == -ELOOP)
+                                        pr_warn_ratelimited(
+                                                "VFS: Lookup of '%s' in %s %s"
+                                                " would have caused loop\n",
+                                                dentry->d_name.name,
+                                                inode->i_sb->s_type->name,
+                                                inode->i_sb->s_id);
                                 dput(alias);
+                        }
                         goto out_nolock;
                 }
         }
@@ -2430,16 +2439,14 @@ static int prepend_name(char **buffer, int *buflen, struct qstr *name)
 /**
  * prepend_path - Prepend path string to a buffer
  * @path: the dentry/vfsmount to report
- * @root: root vfsmnt/dentry (may be modified by this function)
+ * @root: root vfsmnt/dentry
  * @buffer: pointer to the end of the buffer
  * @buflen: pointer to buffer length
  *
  * Caller holds the rename_lock.
- *
- * If path is not reachable from the supplied root, then the value of
- * root is changed (without modifying refcounts).
  */
-static int prepend_path(const struct path *path, struct path *root,
+static int prepend_path(const struct path *path,
+                        const struct path *root,
                         char **buffer, int *buflen)
 {
         struct dentry *dentry = path->dentry;
@@ -2474,10 +2481,10 @@ static int prepend_path(const struct path *path, struct path *root,
                 dentry = parent;
         }
 
-out:
         if (!error && !slash)
                 error = prepend(buffer, buflen, "/", 1);
 
+out:
         br_read_unlock(vfsmount_lock);
         return error;
 
@@ -2491,15 +2498,17 @@ global_root:
                 WARN(1, "Root dentry has weird name <%.*s>\n",
                      (int) dentry->d_name.len, dentry->d_name.name);
         }
-        root->mnt = vfsmnt;
-        root->dentry = dentry;
+        if (!slash)
+                error = prepend(buffer, buflen, "/", 1);
+        if (!error)
+                error = vfsmnt->mnt_ns ? 1 : 2;
         goto out;
 }
 
 /**
  * __d_path - return the path of a dentry
  * @path: the dentry/vfsmount to report
- * @root: root vfsmnt/dentry (may be modified by this function)
+ * @root: root vfsmnt/dentry
  * @buf: buffer to return value in
  * @buflen: buffer length
  *
@@ -2510,10 +2519,10 @@ global_root:
  *
  * "buflen" should be positive.
  *
- * If path is not reachable from the supplied root, then the value of
- * root is changed (without modifying refcounts).
+ * If the path is not reachable from the supplied root, return %NULL.
  */
-char *__d_path(const struct path *path, struct path *root,
+char *__d_path(const struct path *path,
+               const struct path *root,
                char *buf, int buflen)
 {
         char *res = buf + buflen;
@@ -2524,7 +2533,28 @@ char *__d_path(const struct path *path, struct path *root,
         error = prepend_path(path, root, &res, &buflen);
         write_sequnlock(&rename_lock);
 
-        if (error)
+        if (error < 0)
+                return ERR_PTR(error);
+        if (error > 0)
+                return NULL;
+        return res;
+}
+
+char *d_absolute_path(const struct path *path,
+               char *buf, int buflen)
+{
+        struct path root = {};
+        char *res = buf + buflen;
+        int error;
+
+        prepend(&res, &buflen, "\0", 1);
+        write_seqlock(&rename_lock);
+        error = prepend_path(path, &root, &res, &buflen);
+        write_sequnlock(&rename_lock);
+
+        if (error > 1)
+                error = -EINVAL;
+        if (error < 0)
                 return ERR_PTR(error);
         return res;
 }
@@ -2532,8 +2562,9 @@ char *__d_path(const struct path *path, struct path *root,
 /*
  * same as __d_path but appends "(deleted)" for unlinked files.
  */
-static int path_with_deleted(const struct path *path, struct path *root,
-                                 char **buf, int *buflen)
+static int path_with_deleted(const struct path *path,
+                             const struct path *root,
+                             char **buf, int *buflen)
 {
         prepend(buf, buflen, "\0", 1);
         if (d_unlinked(path->dentry)) {
@@ -2570,7 +2601,6 @@ char *d_path(const struct path *path, char *buf, int buflen)
 {
         char *res = buf + buflen;
         struct path root;
-        struct path tmp;
         int error;
 
         /*
@@ -2585,9 +2615,8 @@ char *d_path(const struct path *path, char *buf, int buflen)
 
         get_fs_root(current->fs, &root);
         write_seqlock(&rename_lock);
-        tmp = root;
-        error = path_with_deleted(path, &tmp, &res, &buflen);
-        if (error)
+        error = path_with_deleted(path, &root, &res, &buflen);
+        if (error < 0)
                 res = ERR_PTR(error);
         write_sequnlock(&rename_lock);
         path_put(&root);
@@ -2608,7 +2637,6 @@ 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)
@@ -2616,9 +2644,8 @@ char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
 
         get_fs_root(current->fs, &root);
         write_seqlock(&rename_lock);
-        tmp = root;
-        error = path_with_deleted(path, &tmp, &res, &buflen);
-        if (!error && !path_equal(&tmp, &root))
+        error = path_with_deleted(path, &root, &res, &buflen);
+        if (error > 0)
                 error = prepend_unreachable(&res, &buflen);
         write_sequnlock(&rename_lock);
         path_put(&root);
@@ -2749,19 +2776,18 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
         write_seqlock(&rename_lock);
         if (!d_unlinked(pwd.dentry)) {
                 unsigned long len;
-                struct path tmp = root;
                 char *cwd = page + PAGE_SIZE;
                 int buflen = PAGE_SIZE;
 
                 prepend(&cwd, &buflen, "\0", 1);
-                error = prepend_path(&pwd, &tmp, &cwd, &buflen);
+                error = prepend_path(&pwd, &root, &cwd, &buflen);
                 write_sequnlock(&rename_lock);
 
-                if (error)
+                if (error < 0)
                         goto out;
 
                 /* Unreachable from current root */
-                if (!path_equal(&tmp, &root)) {
+                if (error > 0) {
                         error = prepend_unreachable(&cwd, &buflen);
                         if (error)
                                 goto out;