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

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: d00a1c72f7 ("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: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Eric Biggers 2017-11-02 00:47:12 +00:00 committed by syphyr
parent 26ecd2f35d
commit 4237e3091c
1 changed files with 12 additions and 11 deletions
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23
security/keys/trusted.c
View File

@ -1064,20 +1064,21 @@ static long trusted_read(const struct key *key, char __user *buffer,
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;
}