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Commit 9c6256a5 authored by Xiao Han's avatar Xiao Han Committed by Greg Kroah-Hartman
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usb: misc: ftdi-elan: Fix off-by-one memory corruptions 



This patch fixes fives off-by-one bugs in the ftdi-elan driver code. The
bug can be triggered by plugging a USB adapter for CardBus 3G cards (model
U132 manufactured by Elan Digital Systems, Ltd), causing a kernel panic.
The fix was tested on Ubuntu 14.04.4 with 4.7.0-rc14.2.0-27-generic+ and
4.4.0-22-generic+ kernel. In the ftdi_elan_synchronize function, an
off-by-one memory corruption occurs when packet_bytes is equal or bigger
than m. After having read m bytes, that is bytes_read is equal to m, "
..\x00" is still copied to the stack variable causing an out bounds write
of 4 bytes, which overwrites the stack canary and results in a kernel
panic.

This off-by-one requires physical access to the machine. It is not
exploitable since we have no control on the overwritten data.  Similar
off-by-one bugs have been observed in 4 other functions:
ftdi_elan_stuck_waiting, ftdi_elan_read, ftdi_elan_edset_output and
ftdi_elan_flush_input_fifo.

Reported-by: default avatarAlex Palesandro <palexster@gmail.com>
Signed-off-by: default avatarXiao Han <xiao.han@orange.fr>
Tested-by: default avatarPaul Chaignon <pchaigno@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 28324936

drivers/usb/misc/ftdi-elan.c

+5 −5
Original line number Diff line number Diff line
@@ -665,7 +665,7 @@ static ssize_t ftdi_elan_read(struct file *file, char __user *buffer, 
{

	char data[30 *3 + 4];

	char *d = data;

	int m = (sizeof(data) - 1) / 3;

	int m = (sizeof(data) - 1) / 3 - 1;

	int bytes_read = 0;

	int retry_on_empty = 10;

	int retry_on_timeout = 5;
@@ -1684,7 +1684,7 @@ wait:if (ftdi->disconnected > 0) { 
			int i = 0;

			char data[30 *3 + 4];

			char *d = data;

			int m = (sizeof(data) - 1) / 3;

			int m = (sizeof(data) - 1) / 3 - 1;

			int l = 0;

			struct u132_target *target = &ftdi->target[ed];

			struct u132_command *command = &ftdi->command[
@@ -1876,7 +1876,7 @@ more:{ 
		if (packet_bytes > 2) {

			char diag[30 *3 + 4];

			char *d = diag;

			int m = (sizeof(diag) - 1) / 3;

			int m = (sizeof(diag) - 1) / 3 - 1;

			char *b = ftdi->bulk_in_buffer;

			int bytes_read = 0;

			diag[0] = 0;
@@ -2053,7 +2053,7 @@ static int ftdi_elan_synchronize(struct usb_ftdi *ftdi) 
			if (packet_bytes > 2) {

				char diag[30 *3 + 4];

				char *d = diag;

				int m = (sizeof(diag) - 1) / 3;

				int m = (sizeof(diag) - 1) / 3 - 1;

				char *b = ftdi->bulk_in_buffer;

				int bytes_read = 0;

				unsigned char c = 0;
@@ -2155,7 +2155,7 @@ more:{ 
		if (packet_bytes > 2) {

			char diag[30 *3 + 4];

			char *d = diag;

			int m = (sizeof(diag) - 1) / 3;

			int m = (sizeof(diag) - 1) / 3 - 1;

			char *b = ftdi->bulk_in_buffer;

			int bytes_read = 0;

			diag[0] = 0;