Patch "KEYS: trusted: fix writing past end of buffer in trusted_read()" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     keys-trusted-fix-writing-past-end-of-buffer-in-trusted_read.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From a3c812f7cfd80cf51e8f5b7034f7418f6beb56c1 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Thu, 2 Nov 2017 00:47:12 +0000
Subject: KEYS: trusted: fix writing past end of buffer in trusted_read()

From: Eric Biggers <ebiggers@google.com>

commit a3c812f7cfd80cf51e8f5b7034f7418f6beb56c1 upstream.

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>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 security/keys/trusted.c |   23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -1094,20 +1094,21 @@ static long trusted_read(const struct ke
 	p = rcu_dereference_key(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;
 }
 


Patches currently in stable-queue which might be from ebiggers@google.com are

queue-4.4/keys-trusted-sanitize-all-key-material.patch
queue-4.4/keys-trusted-fix-writing-past-end-of-buffer-in-trusted_read.patch