On 1/12/22 19:27, Kees Cook wrote:
When building with -Warray-bounds, this warning was emitted:
In function 'memset',
inlined from 'vtpm_proxy_fops_read' at drivers/char/tpm/tpm_vtpm_proxy.c:102:2:
./include/linux/fortify-string.h:43:33: warning: '__builtin_memset' pointer overflow between offset 164 and size [2147483648, 4294967295]
[-Warray-bounds]
43 | #define __underlying_memset __builtin_memset
| ^
There was no checking of the req_len value from the device. A malicious
(or buggy) device could end up leaking (and when wiping) memory contents
beyond the end of the proxy buffer.
Cc: Peter Huewe <peterhuewe@xxxxxx>
Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: linux-integrity@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
drivers/char/tpm/tpm_vtpm_proxy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/char/tpm/tpm_vtpm_proxy.c b/drivers/char/tpm/tpm_vtpm_proxy.c
index 91c772e38bb5..5c865987ba5c 100644
--- a/drivers/char/tpm/tpm_vtpm_proxy.c
+++ b/drivers/char/tpm/tpm_vtpm_proxy.c
@@ -91,7 +91,7 @@ static ssize_t vtpm_proxy_fops_read(struct file *filp, char __user *buf,
len = proxy_dev->req_len;
- if (count < len) {
+ if (count < len || len > sizeof(proxy_dev->buffer)) {
mutex_unlock(&proxy_dev->buf_lock);
pr_debug("Invalid size in recv: count=%zd, req_len=%zd\n",
count, len);
Thanks for this patch.
I just want to clarify this. In vtpm_proxy_tpm_op_send() we have the
only place that sets req_len to a value larger than 0:
static int vtpm_proxy_tpm_op_send(struct tpm_chip *chip, u8 *buf, size_t
count)
{
struct proxy_dev *proxy_dev = dev_get_drvdata(&chip->dev);
if (count > sizeof(proxy_dev->buffer)) {
dev_err(&chip->dev,
"Invalid size in send: count=%zd, buffer size=%zd\n",
count, sizeof(proxy_dev->buffer));
return -EIO;
}
[...]
proxy_dev->req_len = count;
memcpy(proxy_dev->buffer, buf, count);
[...]
}
The above makes sure that we cannot copy more bytes into the
proxy_dev->buffer than the what the buffer has bytes for.
It then sets req_len to a valid value that is less or equal to the
buffer size.
Considering this your check above seems to only be there to make the
compiler happy but otherwise I don't see that this is a real problem
with a buffer overflow?!
Nevertheless, let all those compilers be happy:
Reviewed-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
