Patch "KEYS: return full count in keyring_read() if buffer is too small" has been added to the 4.13-stable tree

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

KEYS: return full count in keyring_read() if buffer is too small

to the 4.13-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-return-full-count-in-keyring_read-if-buffer-is-too-small.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Biggers <[email protected]>
Date: Thu, 2 Nov 2017 00:47:03 +0000
Subject: KEYS: return full count in keyring_read() if buffer is too small

From: Eric Biggers <[email protected]>

commit 3239b6f29bdfb4b0a2ba59df995fc9e6f4df7f1f upstream.

Commit e645016abc80 ("KEYS: fix writing past end of user-supplied buffer in keyring_read()") made keyring_read() stop corrupting userspace memory when the user-supplied buffer is too small. However it also made the return value in that case be the short buffer size rather than the size required, yet keyctl_read() is actually documented to return the size required. Therefore, switch it over to the documented behavior.

Note that for now we continue to have it fill the short buffer, since it did that before (pre-v3.13) and dump_key_tree_aux() in keyutils arguably relies on it.

---
 security/keys/keyring.c |   39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

@@ -459,34 +459,33 @@ static long keyring_read(const struct ke
 			 char __user *buffer, size_t buflen)
 {
 	struct keyring_read_iterator_context ctx;
-	unsigned long nr_keys;
-	int ret;
+	long ret;
 
 	kenter("{%d},,%zu", key_serial(keyring), buflen);
 
 	if (buflen & (sizeof(key_serial_t) - 1))
 		return -EINVAL;
 
-	nr_keys = keyring->keys.nr_leaves_on_tree;
-	if (nr_keys == 0)
-		return 0;
-
-	/* Calculate how much data we could return */
-	if (!buffer || !buflen)
-		return nr_keys * sizeof(key_serial_t);
-
-	/* Copy the IDs of the subscribed keys into the buffer */
-	ctx.buffer = (key_serial_t __user *)buffer;
-	ctx.buflen = buflen;
-	ctx.count = 0;
-	ret = assoc_array_iterate(&keyring->keys, keyring_read_iterator, &ctx);
-	if (ret < 0) {
-		kleave(" = %d [iterate]", ret);
-		return ret;
+	/* Copy as many key IDs as fit into the buffer */
+	if (buffer && buflen) {
+		ctx.buffer = (key_serial_t __user *)buffer;
+		ctx.buflen = buflen;
+		ctx.count = 0;
+		ret = assoc_array_iterate(&keyring->keys,
+					  keyring_read_iterator, &ctx);
+		if (ret < 0) {
+			kleave(" = %ld [iterate]", ret);
+			return ret;
+		}
 	}
 
-	kleave(" = %zu [ok]", ctx.count);
-	return ctx.count;
+	/* Return the size of the buffer needed */
+	ret = keyring->keys.nr_leaves_on_tree * sizeof(key_serial_t);
+	if (ret <= buflen)
+		kleave("= %ld [ok]", ret);
+	else
+		kleave("= %ld [buffer too small]", ret);
+	return ret;
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/keys-fix-out-of-bounds-read-during-asn.1-parsing.patch queue-4.13/keys-trusted-fix-writing-past-end-of-buffer-in-trusted_read.patch queue-4.13/keys-return-full-count-in-keyring_read-if-buffer-is-too-small.patch