From 389b185cb2f17fff994dbdf8d4bac003d4b2b6b3 Mon Sep 17 00:00:00 2001 From: Jim Lin Date: Fri, 13 Jan 2017 16:07:58 +0800 Subject: FROMLIST: CHROMIUM: usb: gadget: configfs: Fix KASAN use-after-free When gadget is disconnected, running sequence is like this. . android_work: sent uevent USB_STATE=DISCONNECTED . 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 android_setup+0xb4/0x140 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. BUG=chrome-os-partner:58412 TEST=After smaug device was connected to ubuntu PC host, detached and attached type-C cable quickly several times without seeing "BUG: KASAN: use-after-free in usb_gadget_get_string". Bug: 31614969 Change-Id: I58240ee7c55ae8f8fb8597d14f09c5ac07abb032 Signed-off-by: Jim Lin Signed-off-by: Siqi Lin (am from https://chromium-review.googlesource.com/#/c/428059/3) --- drivers/usb/gadget/configfs.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c index c484d9a..f7d8a3d 100644 --- a/drivers/usb/gadget/configfs.c +++ b/drivers/usb/gadget/configfs.c @@ -130,21 +130,28 @@ struct gadget_config_name { struct list_head list; }; +#define MAX_USB_STRING_LEN 126 +#define MAX_USB_STRING_WITH_NULL_LEN (MAX_USB_STRING_LEN+1) + static int usb_string_copy(const char *s, char **s_copy) { int ret; char *str; char *copy = *s_copy; ret = strlen(s); - if (ret > 126) + if (ret > MAX_USB_STRING_LEN) return -EOVERFLOW; - str = kstrdup(s, GFP_KERNEL); - if (!str) - return -ENOMEM; + if (copy) { + str = copy; + } else { + str = kmalloc(MAX_USB_STRING_WITH_NULL_LEN, GFP_KERNEL); + if (!str) + return -ENOMEM; + } + strncpy(str, s, MAX_USB_STRING_WITH_NULL_LEN); if (str[ret - 1] == '\n') str[ret - 1] = '\0'; - kfree(copy); *s_copy = str; return 0; } -- cgit v1.1