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ovl: fix remove/copy-up race 

ovl_remove_and_whiteout() needs to check if upper dentry exists or not
after having locked upper parent directory.

Previously we used a "type" value computed before locking the upper parent
directory, which is susceptible to racing with copy-up.

There's a similar check in ovl_check_empty_and_clear().  This one is not
actually racy, since copy-up doesn't change the "emptyness" property of a
directory.  Add a comment to this effect, and check the existence of upper
dentry locally to make the code cleaner.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
This commit is contained in:
Miklos Szeredi 2014-11-20 16:39:59 +01:00
parent ef94b1864d
commit a105d685a8
1 changed files with 19 additions and 12 deletions
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31
fs/overlayfs/dir.c
View File

@ -284,8 +284,7 @@ out:
return ERR_PTR(err);
}
static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry,
enum ovl_path_type type)
static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry)
{
int err;
struct dentry *ret = NULL;
@ -294,8 +293,17 @@ static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry,
err = ovl_check_empty_dir(dentry, &list);
if (err)
ret = ERR_PTR(err);
else if (type == OVL_PATH_MERGE)
ret = ovl_clear_empty(dentry, &list);
else {
/*
* If no upperdentry then skip clearing whiteouts.
*
* Can race with copy-up, since we don't hold the upperdir
* mutex. Doesn't matter, since copy-up can't create a
* non-empty directory from an empty one.
*/
if (ovl_dentry_upper(dentry))
ret = ovl_clear_empty(dentry, &list);
}
ovl_cache_free(&list);
@ -487,8 +495,7 @@ out:
return err;
}
static int ovl_remove_and_whiteout(struct dentry *dentry,
enum ovl_path_type type, bool is_dir)
static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir)
{
struct dentry *workdir = ovl_workdir(dentry);
struct inode *wdir = workdir->d_inode;
@ -500,7 +507,7 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
int err;
if (is_dir) {
opaquedir = ovl_check_empty_and_clear(dentry, type);
opaquedir = ovl_check_empty_and_clear(dentry);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir))
goto out;
@ -515,9 +522,10 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
if (IS_ERR(whiteout))
goto out_unlock;
if (type == OVL_PATH_LOWER) {
upper = ovl_dentry_upper(dentry);
if (!upper) {
upper = lookup_one_len(dentry->d_name.name, upperdir,
dentry->d_name.len);
dentry->d_name.len);
err = PTR_ERR(upper);
if (IS_ERR(upper))
goto kill_whiteout;
@ -529,7 +537,6 @@ static int ovl_remove_and_whiteout(struct dentry *dentry,
} else {
int flags = 0;
upper = ovl_dentry_upper(dentry);
if (opaquedir)
upper = opaquedir;
err = -ESTALE;
@ -648,7 +655,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
cap_raise(override_cred->cap_effective, CAP_CHOWN);
old_cred = override_creds(override_cred);
err = ovl_remove_and_whiteout(dentry, type, is_dir);
err = ovl_remove_and_whiteout(dentry, is_dir);
revert_creds(old_cred);
put_cred(override_cred);
@ -781,7 +788,7 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
}
if (overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir) {
opaquedir = ovl_check_empty_and_clear(new, new_type);
opaquedir = ovl_check_empty_and_clear(new);
err = PTR_ERR(opaquedir);
if (IS_ERR(opaquedir)) {
opaquedir = NULL;