From: Dmitry Torokhov dmitry.torokhov@gmail.com
commit b86dab054059b970111b5516ae548efaae5b3aae upstream.
When k_ascii is invoked several times in a row there is a potential for signed integer overflow:
UBSAN: Undefined behaviour in drivers/tty/vt/keyboard.c:888:19 signed integer overflow: 10 * 1111111111 cannot be represented in type 'int' CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.6.11 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: <IRQ> __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xce/0x128 lib/dump_stack.c:118 ubsan_epilogue+0xe/0x30 lib/ubsan.c:154 handle_overflow+0xdc/0xf0 lib/ubsan.c:184 __ubsan_handle_mul_overflow+0x2a/0x40 lib/ubsan.c:205 k_ascii+0xbf/0xd0 drivers/tty/vt/keyboard.c:888 kbd_keycode drivers/tty/vt/keyboard.c:1477 [inline] kbd_event+0x888/0x3be0 drivers/tty/vt/keyboard.c:1495
While it can be worked around by using check_mul_overflow()/ check_add_overflow(), it is better to introduce a separate flag to signal that number pad is being used to compose a symbol, and change type of the accumulator from signed to unsigned, thus avoiding undefined behavior when it overflows.
Reported-by: Kyungtae Kim kt0755@gmail.com Signed-off-by: Dmitry Torokhov dmitry.torokhov@gmail.com Cc: stable stable@vger.kernel.org Link: https://lore.kernel.org/r/20200525232740.GA262061@dtor-ws Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/vt/keyboard.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-)
--- a/drivers/tty/vt/keyboard.c +++ b/drivers/tty/vt/keyboard.c @@ -126,7 +126,11 @@ static DEFINE_SPINLOCK(func_buf_lock); / static unsigned long key_down[BITS_TO_LONGS(KEY_CNT)]; /* keyboard key bitmap */ static unsigned char shift_down[NR_SHIFT]; /* shift state counters.. */ static bool dead_key_next; -static int npadch = -1; /* -1 or number assembled on pad */ + +/* Handles a number being assembled on the number pad */ +static bool npadch_active; +static unsigned int npadch_value; + static unsigned int diacr; static char rep; /* flag telling character repeat */
@@ -816,12 +820,12 @@ static void k_shift(struct vc_data *vc, shift_state &= ~(1 << value);
/* kludge */ - if (up_flag && shift_state != old_state && npadch != -1) { + if (up_flag && shift_state != old_state && npadch_active) { if (kbd->kbdmode == VC_UNICODE) - to_utf8(vc, npadch); + to_utf8(vc, npadch_value); else - put_queue(vc, npadch & 0xff); - npadch = -1; + put_queue(vc, npadch_value & 0xff); + npadch_active = false; } }
@@ -839,7 +843,7 @@ static void k_meta(struct vc_data *vc, u
static void k_ascii(struct vc_data *vc, unsigned char value, char up_flag) { - int base; + unsigned int base;
if (up_flag) return; @@ -853,10 +857,12 @@ static void k_ascii(struct vc_data *vc, base = 16; }
- if (npadch == -1) - npadch = value; - else - npadch = npadch * base + value; + if (!npadch_active) { + npadch_value = 0; + npadch_active = true; + } + + npadch_value = npadch_value * base + value; }
static void k_lock(struct vc_data *vc, unsigned char value, char up_flag)