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ovl: lookup whiteouts outside iterate_dir() 

If jffs2 can deadlock on overlayfs readdir because it takes the same lock
on ->iterate() as in ->lookup().

Fix by moving whiteout checking outside iterate_dir().  Optimized by
collecting potential whiteouts (DT_CHR) in a temporary list and if
non-empty iterating throug these and checking for a 0/0 chardev.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Fixes: 49c21e1cac ("ovl: check whiteout while reading directory")
Reported-by: Roman Yeryomin <leroi.lists@gmail.com>
This commit is contained in:
Miklos Szeredi 2015-06-22 13:53:48 +02:00
parent 7c03b5d45b
commit cdb6727958
1 changed files with 49 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

77
fs/overlayfs/readdir.c
View File

@ -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_entry_find(struct rb_root *root,
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_entry_new(struct dentry *dir,
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 ovl_readdir_data *rdd,
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_readdir_data *rdd,
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_context *ctx, const char *name,
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;
struct ovl_cache_entry *p;
struct dentry *dentry;
const struct cred *old_cred;
struct cred *override_cred;
override_cred = prepare_creds();
if (!override_cred)
return -ENOMEM;
/*
* CAP_DAC_OVERRIDE for lookup
*/
cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
old_cred = override_creds(override_cred);
err = mutex_lock_killable(&dir->d_inode->i_mutex);
if (!err) {
while (rdd->first_maybe_whiteout) {
p = rdd->first_maybe_whiteout;
rdd->first_maybe_whiteout = p->next_maybe_whiteout;
dentry = lookup_one_len(p->name, dir, p->len);
if (!IS_ERR(dentry)) {
p->is_whiteout = ovl_is_whiteout(dentry);
dput(dentry);
}
}
mutex_unlock(&dir->d_inode->i_mutex);
}
revert_creds(old_cred);
put_cred(override_cred);
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 path *realpath,
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 path *realpath,
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;