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ovl: untangle copy up call chain
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In an attempt to dedup ~100 LOC, we ended up creating a tangled call chain,
whose branches merge and diverge in several points according to the
immutable c->tmpfile copy up mode.

This call chain was hard to analyse for locking correctness because the
locking requirements for the c->tmpfile flow were very different from the
locking requirements for the !c->tmpfile flow (i.e. directory vs.  regulare
file copy up).

Split the copy up helpers of the c->tmpfile flow from those of the
!c->tmpfile (i.e. workdir) flow and remove the c->tmpfile mode from copy up
context.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
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Amir Goldstein authored and Miklos Szeredi committed Oct 26, 2018
1 parent 007ea44 commit b10cdcd
Showing 1 changed file with 159 additions and 86 deletions.
245 changes: 159 additions & 86 deletions fs/overlayfs/copy_up.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -395,7 +395,6 @@ struct ovl_copy_up_ctx {
struct dentry *destdir;
struct qstr destname;
struct dentry *workdir;
bool tmpfile;
bool origin;
bool indexed;
bool metacopy;
Expand Down Expand Up @@ -440,62 +439,6 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
return err;
}

static int ovl_install_temp(struct ovl_copy_up_ctx *c, struct dentry *temp,
struct dentry **newdentry)
{
int err;
struct dentry *upper;
struct inode *udir = d_inode(c->destdir);

upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
if (IS_ERR(upper))
return PTR_ERR(upper);

if (c->tmpfile)
err = ovl_do_link(temp, udir, upper);
else
err = ovl_do_rename(d_inode(c->workdir), temp, udir, upper, 0);

if (!err)
*newdentry = dget(c->tmpfile ? upper : temp);
dput(upper);

return err;
}

static struct dentry *ovl_get_tmpfile(struct ovl_copy_up_ctx *c)
{
int err;
struct dentry *temp;
const struct cred *old_creds = NULL;
struct cred *new_creds = NULL;
struct ovl_cattr cattr = {
/* Can't properly set mode on creation because of the umask */
.mode = c->stat.mode & S_IFMT,
.rdev = c->stat.rdev,
.link = c->link
};

err = security_inode_copy_up(c->dentry, &new_creds);
if (err < 0)
return ERR_PTR(err);

if (new_creds)
old_creds = override_creds(new_creds);

if (c->tmpfile)
temp = ovl_do_tmpfile(c->workdir, c->stat.mode);
else
temp = ovl_create_temp(c->workdir, &cattr);

if (new_creds) {
revert_creds(old_creds);
put_cred(new_creds);
}

return temp;
}

static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
{
int err;
Expand Down Expand Up @@ -547,51 +490,189 @@ static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
return err;
}

static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
static struct dentry *ovl_get_workdir_temp(struct ovl_copy_up_ctx *c)
{
int err;
struct dentry *temp;
const struct cred *old_creds = NULL;
struct cred *new_creds = NULL;
struct ovl_cattr cattr = {
/* Can't properly set mode on creation because of the umask */
.mode = c->stat.mode & S_IFMT,
.rdev = c->stat.rdev,
.link = c->link
};

err = security_inode_copy_up(c->dentry, &new_creds);
if (err < 0)
return ERR_PTR(err);

if (new_creds)
old_creds = override_creds(new_creds);

temp = ovl_create_temp(c->workdir, &cattr);

if (new_creds) {
revert_creds(old_creds);
put_cred(new_creds);
}

return temp;
}

/*
* Move temp file from workdir into place on upper dir.
* Used when copying up directories and when upper fs doesn't support O_TMPFILE.
*
* Caller must hold ovl_lock_rename_workdir().
*/
static int ovl_rename_temp(struct ovl_copy_up_ctx *c, struct dentry *temp,
struct dentry **newdentry)
{
int err;
struct dentry *upper;
struct inode *udir = d_inode(c->destdir);

upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
if (IS_ERR(upper))
return PTR_ERR(upper);

err = ovl_do_rename(d_inode(c->workdir), temp, udir, upper, 0);
if (!err)
*newdentry = dget(temp);
dput(upper);

return err;
}

/*
* Copyup using workdir to prepare temp file. Used when copying up directories,
* special files or when upper fs doesn't support O_TMPFILE.
*/
static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
{
struct inode *udir = c->destdir->d_inode;
struct inode *inode;
struct dentry *newdentry = NULL;
struct dentry *temp;
int err;

temp = ovl_get_tmpfile(c);
err = ovl_lock_rename_workdir(c->workdir, c->destdir);
if (err)
return err;

temp = ovl_get_workdir_temp(c);
err = PTR_ERR(temp);
if (IS_ERR(temp))
return PTR_ERR(temp);
goto unlock;

err = ovl_copy_up_inode(c, temp);
if (err)
goto out;
goto cleanup;

if (S_ISDIR(c->stat.mode) && c->indexed) {
err = ovl_create_index(c->dentry, c->lowerpath.dentry, temp);
if (err)
goto out;
goto cleanup;
}

if (c->tmpfile) {
inode_lock_nested(udir, I_MUTEX_PARENT);
err = ovl_install_temp(c, temp, &newdentry);
inode_unlock(udir);
} else {
err = ovl_install_temp(c, temp, &newdentry);
}
err = ovl_rename_temp(c, temp, &newdentry);
if (err)
goto out;
goto cleanup;

if (!c->metacopy)
ovl_set_upperdata(d_inode(c->dentry));
inode = d_inode(c->dentry);
ovl_inode_update(inode, newdentry);
if (S_ISDIR(inode->i_mode))
ovl_set_flag(OVL_WHITEOUTS, inode);
out_dput:
dput(temp);
unlock:
unlock_rename(c->workdir, c->destdir);

return err;

cleanup:
ovl_cleanup(d_inode(c->workdir), temp);
goto out_dput;
}

static struct dentry *ovl_get_tmpfile(struct ovl_copy_up_ctx *c)
{
int err;
struct dentry *temp;
const struct cred *old_creds = NULL;
struct cred *new_creds = NULL;

err = security_inode_copy_up(c->dentry, &new_creds);
if (err < 0)
return ERR_PTR(err);

if (new_creds)
old_creds = override_creds(new_creds);

temp = ovl_do_tmpfile(c->workdir, c->stat.mode);

if (new_creds) {
revert_creds(old_creds);
put_cred(new_creds);
}

return temp;
}

/* Link O_TMPFILE into place on upper dir */
static int ovl_link_tmpfile(struct ovl_copy_up_ctx *c, struct dentry *temp,
struct dentry **newdentry)
{
int err;
struct dentry *upper;
struct inode *udir = d_inode(c->destdir);

inode_lock_nested(udir, I_MUTEX_PARENT);

upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
err = PTR_ERR(upper);
if (IS_ERR(upper))
goto unlock;

err = ovl_do_link(temp, udir, upper);
if (!err)
*newdentry = dget(upper);
dput(upper);

unlock:
inode_unlock(udir);

return err;
}

/* Copyup using O_TMPFILE which does not require cross dir locking */
static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
{
struct dentry *newdentry = NULL;
struct dentry *temp;
int err;

temp = ovl_get_tmpfile(c);
if (IS_ERR(temp))
return PTR_ERR(temp);

err = ovl_copy_up_inode(c, temp);
if (err)
goto out;

err = ovl_link_tmpfile(c, temp, &newdentry);
if (err)
goto out;

if (!c->metacopy)
ovl_set_upperdata(d_inode(c->dentry));
ovl_inode_update(d_inode(c->dentry), newdentry);

out:
if (err && !c->tmpfile)
ovl_cleanup(d_inode(c->workdir), temp);
dput(temp);
return err;

}

/*
Expand Down Expand Up @@ -645,18 +726,10 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
}

/* Should we copyup with O_TMPFILE or with workdir? */
if (S_ISREG(c->stat.mode) && ofs->tmpfile) {
c->tmpfile = true;
err = ovl_copy_up_locked(c);
} else {
err = ovl_lock_rename_workdir(c->workdir, c->destdir);
if (!err) {
err = ovl_copy_up_locked(c);
unlock_rename(c->workdir, c->destdir);
}
}


if (S_ISREG(c->stat.mode) && ofs->tmpfile)
err = ovl_copy_up_tmpfile(c);
else
err = ovl_copy_up_workdir(c);
if (err)
goto out;

Expand Down

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