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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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