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

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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.

Fixes: b2a4df200d ("KEYS: Expand the capacity of a keyring")
Cc: <stable@vger.kernel.org>	[v3.13+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
Eric Biggers 2017-09-18 11:36:45 -07:00 committed by David Howells
parent 7fc0786d95
commit e645016abc
1 changed files with 5 additions and 9 deletions
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14
security/keys/keyring.c
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@ -423,7 +423,7 @@ static void keyring_describe(const struct key *keyring, struct seq_file *m)
}
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 void *object, void *data)
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 key *keyring,
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) {