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upektc_img: Prevent image frame overflow

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The frame length and the offset (which depends on the device-supplied
frame type) are derived from device bytes, so validate both the source
read (against the response buffer) and the destination write (against
the image buffer) before copying.
A malicious or malfunctioning device could otherwise drive a negative
(huge once unsigned) or out-of-bounds length.

Note: the response is reassembled across several USB transfers, so the
bound here is the response buffer capacity rather than a single
transfer's actual_length.

Reported by: Keith Linneman (LinnemanLabs)
This commit is contained in:
Marco Trevisan (Treviño)
2026-07-13 08:13:46 +00:00
committed by Marco Trevisan
parent 07152e43ef
commit 44dd97bf5e
1 changed files with 24 additions and 4 deletions
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libfprint/drivers/upektc_img.c
+24 -4
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@@ -155,7 +155,8 @@ capture_reqs_cb (FpiUsbTransfer *transfer, FpDevice *device,
}
static int
upektc_img_process_image_frame (unsigned char *image_buf, unsigned char *cmd_res)
upektc_img_process_image_frame (unsigned char *image_buf, size_t image_buf_len,
unsigned char *cmd_res, size_t cmd_res_len)
{
int offset = 8;
int len = ((cmd_res[5] & 0x0f) << 8) | (cmd_res[6]);
@@ -168,6 +169,16 @@ upektc_img_process_image_frame (unsigned char *image_buf, unsigned char *cmd_res
}
if (cmd_res[7] == 0x20)
len -= 4;
if (len <= 0 ||
(size_t) offset + (size_t) len > cmd_res_len ||
(size_t) len > image_buf_len)
{
fp_dbg ("Invalid image frame length %d (offset %d, source %zu, dest %zu)",
len, offset, cmd_res_len, image_buf_len);
return 0;
}
memcpy (image_buf, cmd_res + offset, len);
return len;
@@ -321,7 +332,8 @@ capture_read_data_cb (FpiUsbTransfer *transfer, FpDevice *device,
case 0x24:
self->image_size +=
upektc_img_process_image_frame (self->image_bits + self->image_size,
data);
(self->expected_image_size * 2) - self->image_size,
data, MAX_RESPONSE_SIZE);
fpi_ssm_jump_to_state (transfer->ssm,
CAPTURE_ACK_FRAME);
break;
@@ -330,8 +342,16 @@ capture_read_data_cb (FpiUsbTransfer *transfer, FpDevice *device,
case 0x20:
self->image_size +=
upektc_img_process_image_frame (self->image_bits + self->image_size,
data);
BUG_ON (self->image_size != self->expected_image_size);
(self->expected_image_size * 2) - self->image_size,
data, MAX_RESPONSE_SIZE);
if (self->image_size != self->expected_image_size)
{
fp_err ("Image size mismatch: got %zu, expected %zu",
self->image_size, self->expected_image_size);
fpi_ssm_mark_failed (transfer->ssm,
fpi_device_error_new (FP_DEVICE_ERROR_PROTO));
return;
}
fp_dbg ("Image size is %lu",
(gulong) self->image_size);
img = fp_image_new (img_class->img_width, img_class->img_height);