On Thu, 2021-03-11 at 14:42 +0800, Macpaul Lin wrote: > From: Jim Lin <jilin@xxxxxxxxxx> > > 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@xxxxxxxxxx> > Signed-off-by: Macpaul Lin <macpaul.lin@xxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > --- > 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@xxxxxxxxxxxxx> > 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? Thanks! Macpaul Lin > and > Macpaul Lin <macpaul.lin@xxxxxxxxxxxx> 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; > }
