-Patch by: Miklos Szeredi <miklos@szeredi.hu>
-
-Some filesystems (e.g. jffs2) lock the same resources for both readdir
-and lookup, leading to a deadlock in ovl_cache_entry_new, which is called
-from the filldir, and calls lookup itself.
-
---- a/fs/overlayfs/readdir.c
-+++ b/fs/overlayfs/readdir.c
-@@ -23,6 +23,7 @@ struct ovl_cache_entry {
- u64 ino;
- struct list_head l_node;
- struct rb_node node;
-+ struct ovl_cache_entry *next_maybe_whiteout;
- bool is_whiteout;
- char name[];
- };
-@@ -39,7 +40,7 @@ struct ovl_readdir_data {
- struct rb_root root;
- struct list_head *list;
- struct list_head middle;
-- struct dentry *dir;
-+ struct ovl_cache_entry *first_maybe_whiteout;
- int count;
- int err;
- };
-@@ -79,7 +80,7 @@ static struct ovl_cache_entry *ovl_cache
- return NULL;
- }
-
--static struct ovl_cache_entry *ovl_cache_entry_new(struct dentry *dir,
-+static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
- const char *name, int len,
- u64 ino, unsigned int d_type)
- {
-@@ -98,29 +99,8 @@ static struct ovl_cache_entry *ovl_cache
- p->is_whiteout = false;
-
- if (d_type == DT_CHR) {
-- struct dentry *dentry;
-- const struct cred *old_cred;
-- struct cred *override_cred;
--
-- override_cred = prepare_creds();
-- if (!override_cred) {
-- kfree(p);
-- return NULL;
-- }
--
-- /*
-- * CAP_DAC_OVERRIDE for lookup
-- */
-- cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-- old_cred = override_creds(override_cred);
--
-- dentry = lookup_one_len(name, dir, len);
-- if (!IS_ERR(dentry)) {
-- p->is_whiteout = ovl_is_whiteout(dentry);
-- dput(dentry);
-- }
-- revert_creds(old_cred);
-- put_cred(override_cred);
-+ p->next_maybe_whiteout = rdd->first_maybe_whiteout;
-+ rdd->first_maybe_whiteout = p;
- }
- return p;
- }
-@@ -148,7 +128,7 @@ static int ovl_cache_entry_add_rb(struct
- return 0;
- }
-
-- p = ovl_cache_entry_new(rdd->dir, name, len, ino, d_type);
-+ p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
- if (p == NULL)
- return -ENOMEM;
-
-@@ -169,7 +149,7 @@ static int ovl_fill_lower(struct ovl_rea
- if (p) {
- list_move_tail(&p->l_node, &rdd->middle);
- } else {
-- p = ovl_cache_entry_new(rdd->dir, name, namelen, ino, d_type);
-+ p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
- if (p == NULL)
- rdd->err = -ENOMEM;
- else
-@@ -219,6 +199,43 @@ static int ovl_fill_merge(struct dir_con
- return ovl_fill_lower(rdd, name, namelen, offset, ino, d_type);
- }
-
-+static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
-+{
-+ int err = 0;
-+
-+ mutex_lock(&dir->d_inode->i_mutex);
-+ while (rdd->first_maybe_whiteout) {
-+ struct dentry *dentry;
-+ const struct cred *old_cred;
-+ struct cred *override_cred;
-+ struct ovl_cache_entry *p = rdd->first_maybe_whiteout;
-+
-+ rdd->first_maybe_whiteout = p->next_maybe_whiteout;
-+
-+ override_cred = prepare_creds();
-+ if (!override_cred) {
-+ err = -ENOMEM;
-+ break;
-+ }
-+ /*
-+ * CAP_DAC_OVERRIDE for lookup
-+ */
-+ cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-+ old_cred = override_creds(override_cred);
-+
-+ dentry = lookup_one_len(p->name, dir, p->len);
-+ if (!IS_ERR(dentry)) {
-+ p->is_whiteout = ovl_is_whiteout(dentry);
-+ dput(dentry);
-+ }
-+ revert_creds(old_cred);
-+ put_cred(override_cred);
-+ }
-+ mutex_unlock(&dir->d_inode->i_mutex);
-+
-+ return err;
-+}
-+
- static inline int ovl_dir_read(struct path *realpath,
- struct ovl_readdir_data *rdd)
- {
-@@ -229,7 +246,7 @@ static inline int ovl_dir_read(struct pa
- if (IS_ERR(realfile))
- return PTR_ERR(realfile);
-
-- rdd->dir = realpath->dentry;
-+ rdd->first_maybe_whiteout = NULL;
- rdd->ctx.pos = 0;
- do {
- rdd->count = 0;
-@@ -238,6 +255,10 @@ static inline int ovl_dir_read(struct pa
- if (err >= 0)
- err = rdd->err;
- } while (!err && rdd->count);
-+
-+ if (!err && rdd->first_maybe_whiteout)
-+ err = ovl_check_whiteouts(realpath->dentry, rdd);
-+
- fput(realfile);
-
- return err;
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