| Message ID | 20230303071959.144604-3-ebiggers@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fix blk-crypto keyslot race condition | expand |
Hi Eric, On Thu, Mar 2, 2023 at 11:23 PM Eric Biggers <ebiggers@kernel.org> wrote: > > From: Eric Biggers <ebiggers@google.com> > > If blk_crypto_evict_key() sees that the key is still in-use (due to a > bug) or that ->keyslot_evict failed, it currently just returns an error > while leaving the key linked into the keyslot management structures. > > However, blk_crypto_evict_key() is only called in contexts such as inode > eviction where failure is not an option. So actually the caller > proceeds with freeing the blk_crypto_key regardless of the return value > of blk_crypto_evict_key(). > > These two assumptions don't match, and the result is that there can be a > use-after-free in blk_crypto_reprogram_all_keys() after one of these > errors occurs. (Note, these errors *shouldn't* happen; we're just > talking about what happens if they do anyway.) > > Fix this by making blk_crypto_evict_key() unlink the key from the > keyslot management structures even on failure. > > Fixes: 1b2628397058 ("block: Keyslot Manager for Inline Encryption") > Cc: stable@vger.kernel.org > Signed-off-by: Eric Biggers <ebiggers@google.com> > --- > block/blk-crypto-profile.c | 50 +++++++++++++++----------------------- > block/blk-crypto.c | 23 +++++++++++------- > 2 files changed, 33 insertions(+), 40 deletions(-) > > diff --git a/block/blk-crypto-profile.c b/block/blk-crypto-profile.c > index 0307fb0d95d34..1b20ead59f39b 100644 > --- a/block/blk-crypto-profile.c > +++ b/block/blk-crypto-profile.c > @@ -354,22 +354,10 @@ bool __blk_crypto_cfg_supported(struct blk_crypto_profile *profile, > return true; > } > > -/** > - * __blk_crypto_evict_key() - Evict a key from a device. > - * @profile: the crypto profile of the device > - * @key: the key to evict. It must not still be used in any I/O. > - * > - * If the device has keyslots, this finds the keyslot (if any) that contains the > - * specified key and calls the driver's keyslot_evict function to evict it. > - * > - * Otherwise, this just calls the driver's keyslot_evict function if it is > - * implemented, passing just the key (without any particular keyslot). This > - * allows layered devices to evict the key from their underlying devices. > - * > - * Context: Process context. Takes and releases profile->lock. > - * Return: 0 on success or if there's no keyslot with the specified key, -EBUSY > - * if the keyslot is still in use, or another -errno value on other > - * error. > +/* > + * This is an internal function that evicts a key from an inline encryption > + * device that can be either a real device or the blk-crypto-fallback "device". > + * It is used only by blk_crypto_evict_key(); see that function for details. > */ > int __blk_crypto_evict_key(struct blk_crypto_profile *profile, > const struct blk_crypto_key *key) > @@ -389,22 +377,22 @@ int __blk_crypto_evict_key(struct blk_crypto_profile *profile, > > blk_crypto_hw_enter(profile); > slot = blk_crypto_find_keyslot(profile, key); > - if (!slot) > - goto out_unlock; > - > - if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { > - err = -EBUSY; > - goto out_unlock; > + if (slot) { > + if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { > + /* BUG: key is still in use by I/O */ > + err = -EBUSY; > + } else { > + err = profile->ll_ops.keyslot_evict( > + profile, key, > + blk_crypto_keyslot_index(slot)); > + } > + /* > + * Callers may free the key even on error, so unlink the key > + * from the hash table and clear slot->key even on error. > + */ > + hlist_del(&slot->hash_node); > + slot->key = NULL; > } The !slot case still needs to be handled. If profile->num_slots != 0 and !slot, we'll get an invalid index from blk_crypto_keyslot_index. With that change, Reviewed-by: Nathan Huckleberry <nhuck@google.com> Thanks, Huck > - err = profile->ll_ops.keyslot_evict(profile, key, > - blk_crypto_keyslot_index(slot)); > - if (err) > - goto out_unlock; > - > - hlist_del(&slot->hash_node); > - slot->key = NULL; > - err = 0; > -out_unlock: > blk_crypto_hw_exit(profile); > return err; > } > diff --git a/block/blk-crypto.c b/block/blk-crypto.c > index 8e5612364c48c..caa86a210cb6c 100644 > --- a/block/blk-crypto.c > +++ b/block/blk-crypto.c > @@ -399,17 +399,22 @@ int blk_crypto_start_using_key(struct block_device *bdev, > } > > /** > - * blk_crypto_evict_key() - Evict a key from any inline encryption hardware > - * it may have been programmed into > - * @bdev: The block_device who's associated inline encryption hardware this key > - * might have been programmed into > - * @key: The key to evict > + * blk_crypto_evict_key() - Evict a blk_crypto_key from a block_device > + * @bdev: a block_device on which I/O using the key may have been done > + * @key: the key to evict > * > - * Upper layers (filesystems) must call this function to ensure that a key is > - * evicted from any hardware that it might have been programmed into. The key > - * must not be in use by any in-flight IO when this function is called. > + * For a given block_device, this function removes the given blk_crypto_key from > + * the keyslot management structures and evicts it from any underlying hardware > + * keyslot(s) or blk-crypto-fallback keyslot it may have been programmed into. > * > - * Return: 0 on success or if the key wasn't in any keyslot; -errno on error. > + * Upper layers must call this before freeing the blk_crypto_key. It must be > + * called for every block_device the key may have been used on. The key must no > + * longer be in use by any I/O when this function is called. > + * > + * Context: May sleep. > + * Return: 0 on success or if the key wasn't in any keyslot; -errno if the key > + * failed to be evicted from a keyslot or is still in-use. Even on > + * "failure", the key is removed from the keyslot management structures. > */ > int blk_crypto_evict_key(struct block_device *bdev, > const struct blk_crypto_key *key) > -- > 2.39.2 >
On Fri, Mar 03, 2023 at 11:45:00AM -0800, Nathan Huckleberry wrote: > > int __blk_crypto_evict_key(struct blk_crypto_profile *profile, > > const struct blk_crypto_key *key) > > @@ -389,22 +377,22 @@ int __blk_crypto_evict_key(struct blk_crypto_profile *profile, > > > > blk_crypto_hw_enter(profile); > > slot = blk_crypto_find_keyslot(profile, key); > > - if (!slot) > > - goto out_unlock; > > - > > - if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { > > - err = -EBUSY; > > - goto out_unlock; > > + if (slot) { > > + if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { > > + /* BUG: key is still in use by I/O */ > > + err = -EBUSY; > > + } else { > > + err = profile->ll_ops.keyslot_evict( > > + profile, key, > > + blk_crypto_keyslot_index(slot)); > > + } > > + /* > > + * Callers may free the key even on error, so unlink the key > > + * from the hash table and clear slot->key even on error. > > + */ > > + hlist_del(&slot->hash_node); > > + slot->key = NULL; > > } > > The !slot case still needs to be handled. If profile->num_slots != 0 > and !slot, we'll get an invalid index from blk_crypto_keyslot_index. > > With that change, > Reviewed-by: Nathan Huckleberry <nhuck@google.com> > > Thanks, > Huck > > > - err = profile->ll_ops.keyslot_evict(profile, key, > > - blk_crypto_keyslot_index(slot)); > > - if (err) > > - goto out_unlock; > > - > > - hlist_del(&slot->hash_node); > > - slot->key = NULL; > > - err = 0; > > -out_unlock: > > blk_crypto_hw_exit(profile); > > return err; > > } I'm not sure what you're referring to. The !slot case is handled correctly, and it's the same as before. - Eric
You're right. Nevermind. Reviewed-by: Nathan Huckleberry <nhuck@google.com> On Fri, Mar 3, 2023 at 11:50 AM Eric Biggers <ebiggers@kernel.org> wrote: > > On Fri, Mar 03, 2023 at 11:45:00AM -0800, Nathan Huckleberry wrote: > > > int __blk_crypto_evict_key(struct blk_crypto_profile *profile, > > > const struct blk_crypto_key *key) > > > @@ -389,22 +377,22 @@ int __blk_crypto_evict_key(struct blk_crypto_profile *profile, > > > > > > blk_crypto_hw_enter(profile); > > > slot = blk_crypto_find_keyslot(profile, key); > > > - if (!slot) > > > - goto out_unlock; > > > - > > > - if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { > > > - err = -EBUSY; > > > - goto out_unlock; > > > + if (slot) { > > > + if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { > > > + /* BUG: key is still in use by I/O */ > > > + err = -EBUSY; > > > + } else { > > > + err = profile->ll_ops.keyslot_evict( > > > + profile, key, > > > + blk_crypto_keyslot_index(slot)); > > > + } > > > + /* > > > + * Callers may free the key even on error, so unlink the key > > > + * from the hash table and clear slot->key even on error. > > > + */ > > > + hlist_del(&slot->hash_node); > > > + slot->key = NULL; > > > } > > > > The !slot case still needs to be handled. If profile->num_slots != 0 > > and !slot, we'll get an invalid index from blk_crypto_keyslot_index. > > > > With that change, > > Reviewed-by: Nathan Huckleberry <nhuck@google.com> > > > > Thanks, > > Huck > > > > > - err = profile->ll_ops.keyslot_evict(profile, key, > > > - blk_crypto_keyslot_index(slot)); > > > - if (err) > > > - goto out_unlock; > > > - > > > - hlist_del(&slot->hash_node); > > > - slot->key = NULL; > > > - err = 0; > > > -out_unlock: > > > blk_crypto_hw_exit(profile); > > > return err; > > > } > > I'm not sure what you're referring to. The !slot case is handled correctly, and > it's the same as before. > > - Eric
diff --git a/block/blk-crypto-profile.c b/block/blk-crypto-profile.c index 0307fb0d95d34..1b20ead59f39b 100644 --- a/block/blk-crypto-profile.c +++ b/block/blk-crypto-profile.c @@ -354,22 +354,10 @@ bool __blk_crypto_cfg_supported(struct blk_crypto_profile *profile, return true; } -/** - * __blk_crypto_evict_key() - Evict a key from a device. - * @profile: the crypto profile of the device - * @key: the key to evict. It must not still be used in any I/O. - * - * If the device has keyslots, this finds the keyslot (if any) that contains the - * specified key and calls the driver's keyslot_evict function to evict it. - * - * Otherwise, this just calls the driver's keyslot_evict function if it is - * implemented, passing just the key (without any particular keyslot). This - * allows layered devices to evict the key from their underlying devices. - * - * Context: Process context. Takes and releases profile->lock. - * Return: 0 on success or if there's no keyslot with the specified key, -EBUSY - * if the keyslot is still in use, or another -errno value on other - * error. +/* + * This is an internal function that evicts a key from an inline encryption + * device that can be either a real device or the blk-crypto-fallback "device". + * It is used only by blk_crypto_evict_key(); see that function for details. */ int __blk_crypto_evict_key(struct blk_crypto_profile *profile, const struct blk_crypto_key *key) @@ -389,22 +377,22 @@ int __blk_crypto_evict_key(struct blk_crypto_profile *profile, blk_crypto_hw_enter(profile); slot = blk_crypto_find_keyslot(profile, key); - if (!slot) - goto out_unlock; - - if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { - err = -EBUSY; - goto out_unlock; + if (slot) { + if (WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)) { + /* BUG: key is still in use by I/O */ + err = -EBUSY; + } else { + err = profile->ll_ops.keyslot_evict( + profile, key, + blk_crypto_keyslot_index(slot)); + } + /* + * Callers may free the key even on error, so unlink the key + * from the hash table and clear slot->key even on error. + */ + hlist_del(&slot->hash_node); + slot->key = NULL; } - err = profile->ll_ops.keyslot_evict(profile, key, - blk_crypto_keyslot_index(slot)); - if (err) - goto out_unlock; - - hlist_del(&slot->hash_node); - slot->key = NULL; - err = 0; -out_unlock: blk_crypto_hw_exit(profile); return err; } diff --git a/block/blk-crypto.c b/block/blk-crypto.c index 8e5612364c48c..caa86a210cb6c 100644 --- a/block/blk-crypto.c +++ b/block/blk-crypto.c @@ -399,17 +399,22 @@ int blk_crypto_start_using_key(struct block_device *bdev, } /** - * blk_crypto_evict_key() - Evict a key from any inline encryption hardware - * it may have been programmed into - * @bdev: The block_device who's associated inline encryption hardware this key - * might have been programmed into - * @key: The key to evict + * blk_crypto_evict_key() - Evict a blk_crypto_key from a block_device + * @bdev: a block_device on which I/O using the key may have been done + * @key: the key to evict * - * Upper layers (filesystems) must call this function to ensure that a key is - * evicted from any hardware that it might have been programmed into. The key - * must not be in use by any in-flight IO when this function is called. + * For a given block_device, this function removes the given blk_crypto_key from + * the keyslot management structures and evicts it from any underlying hardware + * keyslot(s) or blk-crypto-fallback keyslot it may have been programmed into. * - * Return: 0 on success or if the key wasn't in any keyslot; -errno on error. + * Upper layers must call this before freeing the blk_crypto_key. It must be + * called for every block_device the key may have been used on. The key must no + * longer be in use by any I/O when this function is called. + * + * Context: May sleep. + * Return: 0 on success or if the key wasn't in any keyslot; -errno if the key + * failed to be evicted from a keyslot or is still in-use. Even on + * "failure", the key is removed from the keyslot management structures. */ int blk_crypto_evict_key(struct block_device *bdev, const struct blk_crypto_key *key)