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SubjectRe: [PATCH v4] usb: gadget: configfs: Fix KASAN use-after-free
On Thu, Mar 11, 2021 at 02:53:52PM +0800, Macpaul Lin wrote:
> On Thu, 2021-03-11 at 14:42 +0800, Macpaul Lin wrote:
> > From: Jim Lin <jilin@nvidia.com>
> >
> > When gadget is disconnected, running sequence is like this.
> > . composite_disconnect
> > . Call trace:
> > usb_string_copy+0xd0/0x128
> > gadget_config_name_configuration_store+0x4
> > gadget_config_name_attr_store+0x40/0x50
> > configfs_write_file+0x198/0x1f4
> > vfs_write+0x100/0x220
> > SyS_write+0x58/0xa8
> > . configfs_composite_unbind
> > . configfs_composite_bind
> >
> > In configfs_composite_bind, it has
> > "cn->strings.s = cn->configuration;"
> >
> > When usb_string_copy is invoked. it would
> > allocate memory, copy input string, release previous pointed memory space,
> > and use new allocated memory.
> >
> > When gadget is connected, host sends down request to get information.
> > Call trace:
> > usb_gadget_get_string+0xec/0x168
> > lookup_string+0x64/0x98
> > composite_setup+0xa34/0x1ee8
> >
> > If gadget is disconnected and connected quickly, in the failed case,
> > cn->configuration memory has been released by usb_string_copy kfree but
> > configfs_composite_bind hasn't been run in time to assign new allocated
> > "cn->configuration" pointer to "cn->strings.s".
> >
> > When "strlen(s->s) of usb_gadget_get_string is being executed, the dangling
> > memory is accessed, "BUG: KASAN: use-after-free" error occurs.
> >
> > Signed-off-by: Jim Lin <jilin@nvidia.com>
> > Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
> > Cc: stable@vger.kernel.org
> > ---
> > Changes in v2:
> > Changes in v3:
> > - Change commit description
> > Changes in v4:
> > - Fix build error and adapt patch to kernel-5.12-rc1.
> > Replace definition "MAX_USB_STRING_WITH_NULL_LEN" with
> > "USB_MAX_STRING_WITH_NULL_LEN".
> > - Note: The patch v2 and v3 has been verified by
> > Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> > http://spinics.net/lists/kernel/msg3840792.html
>
> Dear Cascardo,
>
> Would you please help to confirm if you've tested it on Linux PC,
> Chrome OS, or an Android OS?

I tested v3 on Ubuntu GNU/Linux. I will test v4.

Cascardo.

>
> Thanks!
> Macpaul Lin
>
> > and
> > Macpaul Lin <macpaul.lin@mediatek.com> on Android kernels.
> > http://lkml.org/lkml/2020/6/11/8
> > - The patch is suggested to be applied to LTS versions.
> >
> > drivers/usb/gadget/configfs.c | 14 ++++++++++----
> > 1 file changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
> > index 0d56f33..15a607c 100644
> > --- a/drivers/usb/gadget/configfs.c
> > +++ b/drivers/usb/gadget/configfs.c
> > @@ -97,6 +97,8 @@ struct gadget_config_name {
> > struct list_head list;
> > };
> >
> > +#define USB_MAX_STRING_WITH_NULL_LEN (USB_MAX_STRING_LEN+1)
> > +
> > static int usb_string_copy(const char *s, char **s_copy)
> > {
> > int ret;
> > @@ -106,12 +108,16 @@ static int usb_string_copy(const char *s, char **s_copy)
> > if (ret > USB_MAX_STRING_LEN)
> > return -EOVERFLOW;
> >
> > - str = kstrdup(s, GFP_KERNEL);
> > - if (!str)
> > - return -ENOMEM;
> > + if (copy) {
> > + str = copy;
> > + } else {
> > + str = kmalloc(USB_MAX_STRING_WITH_NULL_LEN, GFP_KERNEL);
> > + if (!str)
> > + return -ENOMEM;
> > + }
> > + strcpy(str, s);
> > if (str[ret - 1] == '\n')
> > str[ret - 1] = '\0';
> > - kfree(copy);
> > *s_copy = str;
> > return 0;
> > }
>

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