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-rw-r--r--target/linux/generic/patches-4.0/140-overlayfs_readdir_locking_fix.patch148
1 files changed, 148 insertions, 0 deletions
diff --git a/target/linux/generic/patches-4.0/140-overlayfs_readdir_locking_fix.patch b/target/linux/generic/patches-4.0/140-overlayfs_readdir_locking_fix.patch
new file mode 100644
index 0000000000..67dff987d3
--- /dev/null
+++ b/target/linux/generic/patches-4.0/140-overlayfs_readdir_locking_fix.patch
@@ -0,0 +1,148 @@
+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;