From: Amir Goldstein <amir73il@gmail.com>
To: Colin Ian King <colin.king@canonical.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
overlayfs <linux-unionfs@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: ovl: uninitialized pointer read in ovl_lookup_real_one
Date: Sat, 24 Jul 2021 10:36:05 +0300 [thread overview]
Message-ID: <CAOQ4uxgbqyyhQ+78j0L+GxkEJ8rOW43X9ann_kMs1098WkNe8Q@mail.gmail.com> (raw)
In-Reply-To: <737687ee-3449-aa3d-ee29-bd75ca0a18a9@canonical.com>
On Sat, Jul 24, 2021 at 1:26 AM Colin Ian King <colin.king@canonical.com> wrote:
>
> Hi,
>
> Static analysis with Coverity has detected an uninitialized pointer read
> in function ovl_lookup_real_one in fs/overlayfs/export.c
>
> The issue was introduced with the following commit:
>
> commit 3985b70a3e3f58109dc6ae347eafe6e8610be41e
> Author: Amir Goldstein <amir73il@gmail.com>
> Date: Thu Dec 28 18:36:16 2017 +0200
>
> ovl: decode connected upper dir file handles
>
> The analysis is as follows:
>
> 365static struct dentry *ovl_lookup_real_one(struct dentry *connected,
> 366 struct dentry *real,
> 367 const struct ovl_layer *layer)
> 368{
> 369 struct inode *dir = d_inode(connected);
> 370 struct dentry *this, *parent = NULL;
>
> 1. var_decl: Declaring variable name without initializer.
>
> 371 struct name_snapshot name;
> 372 int err;
> 373
> 374 /*
> 375 * Lookup child overlay dentry by real name. The dir mutex
> protects us
> 376 * from racing with overlay rename. If the overlay dentry
> that is above
> 377 * real has already been moved to a parent that is not under the
> 378 * connected overlay dir, we return -ECHILD and restart the
> lookup of
> 379 * connected real path from the top.
> 380 */
> 381 inode_lock_nested(dir, I_MUTEX_PARENT);
> 382 err = -ECHILD;
> 383 parent = dget_parent(real);
>
> 2. Condition ovl_dentry_real_at(connected, layer->idx) != parent,
> taking true branch.
>
> 384 if (ovl_dentry_real_at(connected, layer->idx) != parent)
>
> 3. Jumping to label fail.
>
> 385 goto fail;
> 386
> 387 /*
> 388 * We also need to take a snapshot of real dentry name to
> protect us
> 389 * from racing with underlying layer rename. In this case, we
> don't
> 390 * care about returning ESTALE, only from dereferencing a
> free name
> 391 * pointer because we hold no lock on the real dentry.
> 392 */
> 393 take_dentry_name_snapshot(&name, real);
> 394 this = lookup_one_len(name.name.name, connected, name.name.len);
> 395 err = PTR_ERR(this);
> 396 if (IS_ERR(this)) {
> 397 goto fail;
> 398 } else if (!this || !this->d_inode) {
> 399 dput(this);
> 400 err = -ENOENT;
> 401 goto fail;
> 402 } else if (ovl_dentry_real_at(this, layer->idx) != real) {
> 403 dput(this);
> 404 err = -ESTALE;
> 405 goto fail;
> 406 }
> 407
> 408out:
>
> Uninitialized pointer read
> 6. uninit_use_in_call: Using uninitialized value name.name.name when
> calling release_dentry_name_snapshot.
>
> 409 release_dentry_name_snapshot(&name);
> 410 dput(parent);
> 411 inode_unlock(dir);
> 412 return this;
> 413
> 414fail:
>
> 4. Condition ___ratelimit(&_rs, <anonymous>), taking false branch
> .
> 415 pr_warn_ratelimited("failed to lookup one by real (%pd2,
> layer=%d, connected=%pd2, err=%i)\n",
> 416 real, layer->idx, connected, err);
> 417 this = ERR_PTR(err);
>
> 5. Jumping to label out.
>
> 418 goto out;
> 419}
>
> The error exit path on line 395 ends up with an uninitialized structure
> name being passed to function release_dentry_name_snapshot() on line 409
> and this accesses the pointer name.name.name, see /fs/dcache.c as follows:
>
> 303void release_dentry_name_snapshot(struct name_snapshot *name)
> 304{
>
> 1. read_value: Reading value name->name.name.
> 2. Condition !!(name->name.name != name->inline_name), taking true
> branch.
>
> 305 if (unlikely(name->name.name != name->inline_name)) {
> 306 struct external_name *p;
>
> 3. Condition 0 /* !!(!__builtin_types_compatible_p() &&
> !__builtin_types_compatible_p()) */, taking false branch.
>
>
> I suspect name should be initialized in line 371, e.g. name = { } and a
> null name check should be performed on line 409 before calling
> release_dentry_name_snapshot, but this seems a bit message as a fix.
>
Thanks for the report.
A simpler fix is to move take_dentry_name_snapshot() to top of the
function before goto fail.
Thanks,
Amir.
> Colin
next prev parent reply other threads:[~2021-07-24 7:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-23 22:26 ovl: uninitialized pointer read in ovl_lookup_real_one Colin Ian King
2021-07-24 7:36 ` Amir Goldstein [this message]
2021-08-06 8:22 ` Miklos Szeredi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAOQ4uxgbqyyhQ+78j0L+GxkEJ8rOW43X9ann_kMs1098WkNe8Q@mail.gmail.com \
--to=amir73il@gmail.com \
--cc=colin.king@canonical.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-unionfs@vger.kernel.org \
--cc=miklos@szeredi.hu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).