From: Kyungtae Kim <kt0755@xxxxxxxxx> commit 15753588bcd4bbffae1cca33c8ced5722477fe1f upstream. FuzzUSB (a variant of syzkaller) found an illegal array access using an incorrect index while binding a gadget with UDC. Reference: https://www.spinics.net/lists/linux-usb/msg194331.html This bug occurs when a size variable used for a buffer is misused to access its strcpy-ed buffer. Given a buffer along with its size variable (taken from user input), from which, a new buffer is created using kstrdup(). Due to the original buffer containing 0 value in the middle, the size of the kstrdup-ed buffer becomes smaller than that of the original. So accessing the kstrdup-ed buffer with the same size variable triggers memory access violation. The fix makes sure no zero value in the buffer, by comparing the strlen() of the orignal buffer with the size variable, so that the access to the kstrdup-ed buffer is safe. BUG: KASAN: slab-out-of-bounds in gadget_dev_desc_UDC_store+0x1ba/0x200 drivers/usb/gadget/configfs.c:266 Read of size 1 at addr ffff88806a55dd7e by task syz-executor.0/17208 CPU: 2 PID: 17208 Comm: syz-executor.0 Not tainted 5.6.8 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xce/0x128 lib/dump_stack.c:118 print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374 __kasan_report+0x131/0x1b0 mm/kasan/report.c:506 kasan_report+0x12/0x20 mm/kasan/common.c:641 __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132 gadget_dev_desc_UDC_store+0x1ba/0x200 drivers/usb/gadget/configfs.c:266 flush_write_buffer fs/configfs/file.c:251 [inline] configfs_write_file+0x2f1/0x4c0 fs/configfs/file.c:283 __vfs_write+0x85/0x110 fs/read_write.c:494 vfs_write+0x1cd/0x510 fs/read_write.c:558 ksys_write+0x18a/0x220 fs/read_write.c:611 __do_sys_write fs/read_write.c:623 [inline] __se_sys_write fs/read_write.c:620 [inline] __x64_sys_write+0x73/0xb0 fs/read_write.c:620 do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294 entry_SYSCALL_64_after_hwframe+0x49/0xbe Signed-off-by: Kyungtae Kim <kt0755@xxxxxxxxx> Reported-and-tested-by: Kyungtae Kim <kt0755@xxxxxxxxx> Cc: Felipe Balbi <balbi@xxxxxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20200510054326.GA19198@pizza01 Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/usb/gadget/configfs.c | 3 +++ 1 file changed, 3 insertions(+) --- a/drivers/usb/gadget/configfs.c +++ b/drivers/usb/gadget/configfs.c @@ -259,6 +259,9 @@ static ssize_t gadget_dev_desc_UDC_store char *name; int ret; + if (strlen(page) < len) + return -EOVERFLOW; + name = kstrdup(page, GFP_KERNEL); if (!name) return -ENOMEM;
