[PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read()

[PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read()

[Eric Biggers]

From: Eric Biggers <ebiggers@google.com>

When calling keyctl_read() on a key of type "trusted", if the
user-supplied buffer was too small, the kernel ignored the buffer length
and just wrote past the end of the buffer, potentially corrupting
userspace memory.  Fix it by instead returning the size required, as per
the documentation for keyctl_read().

We also don't even fill the buffer at all in this case, as this is
slightly easier to implement than doing a short read, and either
behavior appears to be permitted.  It also makes it match the behavior
of the "encrypted" key type.

Fixes: d00a1c72f7f4 ("keys: add new trusted key-type")
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Cc: <stable@vger.kernel.org> # v2.6.38+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 security/keys/trusted.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index bd85315cbfeb..98aa89ff7bfd 100644
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -1147,20 +1147,21 @@ static long trusted_read(const struct key *key, char __user *buffer,
 	p = dereference_key_locked(key);
 	if (!p)
 		return -EINVAL;
-	if (!buffer || buflen <= 0)
-		return 2 * p->blob_len;
-	ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL);
-	if (!ascii_buf)
-		return -ENOMEM;
 
-	bufp = ascii_buf;
-	for (i = 0; i < p->blob_len; i++)
-		bufp = hex_byte_pack(bufp, p->blob[i]);
-	if ((copy_to_user(buffer, ascii_buf, 2 * p->blob_len)) != 0) {
+	if (buffer && buflen >= 2 * p->blob_len) {
+		ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL);
+		if (!ascii_buf)
+			return -ENOMEM;
+
+		bufp = ascii_buf;
+		for (i = 0; i < p->blob_len; i++)
+			bufp = hex_byte_pack(bufp, p->blob[i]);
+		if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) {
+			kzfree(ascii_buf);
+			return -EFAULT;
+		}
 		kzfree(ascii_buf);
-		return -EFAULT;
 	}
-	kzfree(ascii_buf);
 	return 2 * p->blob_len;
 }
 
-- 
2.15.0.rc2.357.g7e34df9404-goog

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[PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read()

[Mimi Zohar]

On Thu, 2017-10-26 at 13:57 -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> When calling keyctl_read() on a key of type "trusted", if the
> user-supplied buffer was too small, the kernel ignored the buffer length
> and just wrote past the end of the buffer, potentially corrupting
> userspace memory.  Fix it by instead returning the size required, as per
> the documentation for keyctl_read().
> 
> We also don't even fill the buffer at all in this case, as this is
> slightly easier to implement than doing a short read, and either
> behavior appears to be permitted.  It also makes it match the behavior
> of the "encrypted" key type.
> 
> Fixes: d00a1c72f7f4 ("keys: add new trusted key-type")
> Reported-by: Ben Hutchings <ben@decadent.org.uk>
> Cc: <stable@vger.kernel.org> # v2.6.38+
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Thanks!

Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

> ---
>  security/keys/trusted.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/security/keys/trusted.c b/security/keys/trusted.c
> index bd85315cbfeb..98aa89ff7bfd 100644
> --- a/security/keys/trusted.c
> +++ b/security/keys/trusted.c
> @@ -1147,20 +1147,21 @@ static long trusted_read(const struct key *key, char __user *buffer,
>  	p = dereference_key_locked(key);
>  	if (!p)
>  		return -EINVAL;
> -	if (!buffer || buflen <= 0)
> -		return 2 * p->blob_len;
> -	ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL);
> -	if (!ascii_buf)
> -		return -ENOMEM;
> 
> -	bufp = ascii_buf;
> -	for (i = 0; i < p->blob_len; i++)
> -		bufp = hex_byte_pack(bufp, p->blob[i]);
> -	if ((copy_to_user(buffer, ascii_buf, 2 * p->blob_len)) != 0) {
> +	if (buffer && buflen >= 2 * p->blob_len) {
> +		ascii_buf = kmalloc(2 * p->blob_len, GFP_KERNEL);
> +		if (!ascii_buf)
> +			return -ENOMEM;
> +
> +		bufp = ascii_buf;
> +		for (i = 0; i < p->blob_len; i++)
> +			bufp = hex_byte_pack(bufp, p->blob[i]);
> +		if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) {
> +			kzfree(ascii_buf);
> +			return -EFAULT;
> +		}
>  		kzfree(ascii_buf);
> -		return -EFAULT;
>  	}
> -	kzfree(ascii_buf);
>  	return 2 * p->blob_len;
>  }
> 

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[PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read()

[James Morris]

On Thu, 26 Oct 2017, Eric Biggers wrote:

> From: Eric Biggers <ebiggers@google.com>
> 
> When calling keyctl_read() on a key of type "trusted", if the
> user-supplied buffer was too small, the kernel ignored the buffer length
> and just wrote past the end of the buffer, potentially corrupting
> userspace memory.  Fix it by instead returning the size required, as per
> the documentation for keyctl_read().
> 
> We also don't even fill the buffer at all in this case, as this is
> slightly easier to implement than doing a short read, and either
> behavior appears to be permitted.  It also makes it match the behavior
> of the "encrypted" key type.
> 
> Fixes: d00a1c72f7f4 ("keys: add new trusted key-type")
> Reported-by: Ben Hutchings <ben@decadent.org.uk>
> Cc: <stable@vger.kernel.org> # v2.6.38+
> Signed-off-by: Eric Biggers <ebiggers@google.com>


Reviewed-by: James Morris <james.l.morris@oracle.com>



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James Morris
<james.l.morris@oracle.com>

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[PATCH] KEYS: trusted: fix writing past end of buffer in trusted_read()

[James Morris]

On Thu, 26 Oct 2017, Eric Biggers wrote:

> From: Eric Biggers <ebiggers@google.com>


David, this needs to go to Linus.

Are you planning on pushing out more fixes for this -rc or shuld I just 
send it up via my tree?


-- 
James Morris
<james.l.morris@oracle.com>

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