From: Eugeniu Rosca <erosca@de.adit-jv.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Felipe Balbi <balbi@kernel.org>,
Andrew Gabbasov <andrew_gabbasov@mentor.com>
Cc: <linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
Eugeniu Rosca <erosca@de.adit-jv.com>,
Eugeniu Rosca <roscaeugeniu@gmail.com>
Subject: Re: [PATCH] usb: gadget: f_fs: Fix setting of device and driver data cross-references
Date: Fri, 4 Jun 2021 13:05:03 +0200 [thread overview]
Message-ID: <20210604110503.GA23002@vmlxhi-102.adit-jv.com> (raw)
In-Reply-To: <20210603171507.22514-1-andrew_gabbasov@mentor.com>
Hello,
On Thu, Jun 03, 2021 at 12:15:07PM -0500, Andrew Gabbasov wrote:
> FunctionFS device structure 'struct ffs_dev' and driver data structure
> 'struct ffs_data' are bound to each other with cross-reference pointers
> 'ffs_data->private_data' and 'ffs_dev->ffs_data'. While the first one
> is supposed to be valid through the whole life of 'struct ffs_data'
> (and while 'struct ffs_dev' exists non-freed), the second one is cleared
> in 'ffs_closed()' (called from 'ffs_data_reset()' or the last
> 'ffs_data_put()'). This can be called several times, alternating in
> different order with 'ffs_free_inst()', that, if possible, clears
> the other cross-reference.
>
> As a result, different cases of these calls order may leave stale
> cross-reference pointers, used when the pointed structure is already
> freed. Even if it occasionally doesn't cause kernel crash, this error
> is reported by KASAN-enabled kernel configuration.
>
> For example, the case [last 'ffs_data_put()' - 'ffs_free_inst()'] was
> fixed by commit cdafb6d8b8da ("usb: gadget: f_fs: Fix use-after-free in
> ffs_free_inst").
>
> The other case ['ffs_data_reset()' - 'ffs_free_inst()' - 'ffs_data_put()']
> now causes KASAN reported error [1], when 'ffs_data_reset()' clears
> 'ffs_dev->ffs_data', then 'ffs_free_inst()' frees the 'struct ffs_dev',
> but can't clear 'ffs_data->private_data', which is then accessed
> in 'ffs_closed()' called from 'ffs_data_put()'. This happens since
> 'ffs_dev->ffs_data' reference is cleared too early.
>
> Moreover, one more use case, when 'ffs_free_inst()' is called immediately
> after mounting FunctionFS device (that is before the descriptors are
> written and 'ffs_ready()' is called), and then 'ffs_data_reset()'
> or 'ffs_data_put()' is called from accessing "ep0" file or unmounting
> the device. This causes KASAN error report like [2], since
> 'ffs_dev->ffs_data' is not yet set when 'ffs_free_inst()' can't properly
> clear 'ffs_data->private_data', that is later accessed to freed structure.
I confirm there are at least two KASAN use-after-free issues
consistently/100% reproducible on v5.13-rc4-88-gf88cd3fb9df2:
https://gist.github.com/erosca/b5976a96789e574b319cb9e076938b5c
https://gist.github.com/erosca/4ded55ed32f0133bc2f4ccfe821c7776
These two can no longer be seen after the patch is applied.
In addition, below static analysis tools did not spot any regressions:
cppcheck 2.4, smatch v0.5.0-7445-g58776ae33ae8, make W=1, coccicheck
Reviewed-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Tested-by: Eugeniu Rosca <erosca@de.adit-jv.com>
--
Best regards,
Eugeniu Rosca
next prev parent reply other threads:[~2021-06-04 11:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-03 17:15 [PATCH] usb: gadget: f_fs: Fix setting of device and driver data cross-references Andrew Gabbasov
2021-06-04 11:05 ` Eugeniu Rosca [this message]
2021-07-02 15:01 ` Macpaul Lin
2021-07-02 18:49 ` Andrew Gabbasov
2021-07-02 18:49 ` [PATCH v4.14] " Andrew Gabbasov
2021-07-05 7:07 ` Greg Kroah-Hartman
2021-07-05 10:24 ` Andrew Gabbasov
2021-07-05 10:42 ` 'Greg Kroah-Hartman'
2021-07-11 15:37 ` Andrew Gabbasov
2021-07-11 15:51 ` Andrew Gabbasov
2021-07-11 16:07 ` Greg Kroah-Hartman
2021-07-11 16:44 ` Andrew Gabbasov
2021-07-15 12:01 ` 'Greg Kroah-Hartman'
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