The patch below does not apply to the 3.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

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

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 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

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; }