Patch "KEYS: fix writing past end of user-supplied buffer in keyring_read()" 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: fix writing past end of user-supplied buffer in keyring_read()

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-fix-writing-past-end-of-user-supplied-buffer-in-keyring_read.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: Mon, 18 Sep 2017 11:36:45 -0700
Subject: KEYS: fix writing past end of user-supplied buffer in keyring_read()

From: Eric Biggers <[email protected]>

commit e645016abc803dafc75e4b8f6e4118f088900ffb upstream.

Userspace can call keyctl_read() on a keyring to get the list of IDs of keys in the keyring. But if the user-supplied buffer is too small, the kernel would write the full list anyway --- which will corrupt whatever userspace memory happened to be past the end of the buffer. Fix it by only filling the space that is available.

---
 security/keys/keyring.c |   14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

@@ -423,7 +423,7 @@ static void keyring_describe(const struc
 }
 
 struct keyring_read_iterator_context {
-	size_t			qty;
+	size_t			buflen;
 	size_t			count;
 	key_serial_t __user	*buffer;
 };

@@ -435,9 +435,9 @@ static int keyring_read_iterator(const v
 	int ret;
 
 	kenter("{%s,%d},,{%zu/%zu}",
-	       key->type->name, key->serial, ctx->count, ctx->qty);
+	       key->type->name, key->serial, ctx->count, ctx->buflen);
 
-	if (ctx->count >= ctx->qty)
+	if (ctx->count >= ctx->buflen)
 		return 1;
 
 	ret = put_user(key->serial, ctx->buffer);

@@ -472,16 +472,12 @@ static long keyring_read(const struct ke
 		return 0;
 
 	/* Calculate how much data we could return */
-	ctx.qty = nr_keys * sizeof(key_serial_t);
-
 	if (!buffer || !buflen)
-		return ctx.qty;
-
-	if (buflen > ctx.qty)
-		ctx.qty = 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) {

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

queue-4.13/keys-prevent-creating-a-different-user-s-keyrings.patch queue-4.13/keys-fix-writing-past-end-of-user-supplied-buffer-in-keyring_read.patch