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We miss to take the crypto_alg_sem semaphore when traversing the
crypto_alg_list for CRYPTO_MSG_GETALG dumps. This allows a race with
crypto_unregister_alg() removing algorithms from the list while we're
still traversing it, thereby leading to a use-after-free as show below:

[ 3482.071639] general protection fault: 0000 [#1] SMP
[ 3482.075639] Modules linked in: aes_x86_64 glue_helper lrw ablk_helper cryptd gf128mul ipv6 pcspkr serio_raw virtio_net microcode virtio_pci virtio_ring virtio sr_mod cdrom [last unloaded: aesni_intel]
[ 3482.075639] CPU: 1 PID: 11065 Comm: crconf Not tainted 4.3.4-grsec+ #126
[ 3482.075639] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[ 3482.075639] task: ffff88001cd41a40 ti: ffff88001cd422c8 task.ti: ffff88001cd422c8
[ 3482.075639] RIP: 0010:[<ffffffff93722bd3>]  [<ffffffff93722bd3>] strncpy+0x13/0x30
[ 3482.075639] RSP: 0018:ffff88001f713b60  EFLAGS: 00010202
[ 3482.075639...