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Subject[PATCH] KEYS: fix writing past end of user-supplied buffer in keyring_read()
Date
From: Eric Biggers <ebiggers@google.com>

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: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
Cc: <stable@vger.kernel.org> [v3.13+]
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
security/keys/keyring.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index d8d08bd9c159..4fa82a8a9c0e 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -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) {
--
2.14.1.690.gbb1197296e-goog
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