[pve-devel] [PATCH kernel] cherry-pick fix for CVE-2016-4470

Wolfgang Bumiller w.bumiller at proxmox.com
Thu Jul 14 12:31:02 CEST 2016


Applied

On Wed, Jul 13, 2016 at 03:28:14PM +0200, Fabian Grünbichler wrote:
> ---
>  ...470-KEYS-potential-uninitialized-variable.patch | 94 ++++++++++++++++++++++
>  Makefile                                           |  1 +
>  2 files changed, 95 insertions(+)
>  create mode 100644 CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
> 
> diff --git a/CVE-2016-4470-KEYS-potential-uninitialized-variable.patch b/CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
> new file mode 100644
> index 0000000..052436d
> --- /dev/null
> +++ b/CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
> @@ -0,0 +1,94 @@
> +From edd3cde476d196ebdc771a8fa789d2f4de52ae72 Mon Sep 17 00:00:00 2001
> +From: Dan Carpenter <dan.carpenter at oracle.com>
> +Date: Wed, 13 Jul 2016 11:43:47 +0100
> +Subject: [PATCH] KEYS: potential uninitialized variable
> +
> +If __key_link_begin() failed then "edit" would be uninitialized.  I've
> +added a check to fix that.
> +
> +This allows a random user to crash the kernel, though it's quite
> +difficult to achieve.  There are three ways it can be done as the user
> +would have to cause an error to occur in __key_link():
> +
> + (1) Cause the kernel to run out of memory.  In practice, this is difficult
> +     to achieve without ENOMEM cropping up elsewhere and aborting the
> +     attempt.
> +
> + (2) Revoke the destination keyring between the keyring ID being looked up
> +     and it being tested for revocation.  In practice, this is difficult to
> +     time correctly because the KEYCTL_REJECT function can only be used
> +     from the request-key upcall process.  Further, users can only make use
> +     of what's in /sbin/request-key.conf, though this does including a
> +     rejection debugging test - which means that the destination keyring
> +     has to be the caller's session keyring in practice.
> +
> + (3) Have just enough key quota available to create a key, a new session
> +     keyring for the upcall and a link in the session keyring, but not then
> +     sufficient quota to create a link in the nominated destination keyring
> +     so that it fails with EDQUOT.
> +
> +The bug can be triggered using option (3) above using something like the
> +following:
> +
> +	echo 80 >/proc/sys/kernel/keys/root_maxbytes
> +	keyctl request2 user debug:fred negate @t
> +
> +The above sets the quota to something much lower (80) to make the bug
> +easier to trigger, but this is dependent on the system.  Note also that
> +the name of the keyring created contains a random number that may be
> +between 1 and 10 characters in size, so may throw the test off by
> +changing the amount of quota used.
> +
> +Assuming the failure occurs, something like the following will be seen:
> +
> +	kfree_debugcheck: out of range ptr 6b6b6b6b6b6b6b68h
> +	------------[ cut here ]------------
> +	kernel BUG at ../mm/slab.c:2821!
> +	...
> +	RIP: 0010:[<ffffffff811600f9>] kfree_debugcheck+0x20/0x25
> +	RSP: 0018:ffff8804014a7de8  EFLAGS: 00010092
> +	RAX: 0000000000000034 RBX: 6b6b6b6b6b6b6b68 RCX: 0000000000000000
> +	RDX: 0000000000040001 RSI: 00000000000000f6 RDI: 0000000000000300
> +	RBP: ffff8804014a7df0 R08: 0000000000000001 R09: 0000000000000000
> +	R10: ffff8804014a7e68 R11: 0000000000000054 R12: 0000000000000202
> +	R13: ffffffff81318a66 R14: 0000000000000000 R15: 0000000000000001
> +	...
> +	Call Trace:
> +	  kfree+0xde/0x1bc
> +	  assoc_array_cancel_edit+0x1f/0x36
> +	  __key_link_end+0x55/0x63
> +	  key_reject_and_link+0x124/0x155
> +	  keyctl_reject_key+0xb6/0xe0
> +	  keyctl_negate_key+0x10/0x12
> +	  SyS_keyctl+0x9f/0xe7
> +	  do_syscall_64+0x63/0x13a
> +	  entry_SYSCALL64_slow_path+0x25/0x25
> +
> +Fixes: f70e2e06196a ('KEYS: Do preallocation for __key_link()')
> +Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
> +Signed-off-by: David Howells <dhowells at redhat.com>
> +cc: stable at vger.kernel.org
> +Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> +(cherry picked from commit 38327424b40bcebe2de92d07312c89360ac9229a)
> +CVE-2016-4470
> +Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
> +---
> + security/keys/key.c | 2 +-
> + 1 file changed, 1 insertion(+), 1 deletion(-)
> +
> +diff --git a/security/keys/key.c b/security/keys/key.c
> +index 2779d13..1d2d3a9 100644
> +--- a/security/keys/key.c
> ++++ b/security/keys/key.c
> +@@ -580,7 +580,7 @@ int key_reject_and_link(struct key *key,
> + 
> + 	mutex_unlock(&key_construction_mutex);
> + 
> +-	if (keyring)
> ++	if (keyring && link_ret == 0)
> + 		__key_link_end(keyring, &key->index_key, edit);
> + 
> + 	/* wake up anyone waiting for a key to be constructed */
> +-- 
> +2.1.4
> +
> diff --git a/Makefile b/Makefile
> index 7936548..933adf9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -257,6 +257,7 @@ ${KERNEL_SRC}/README ${KERNEL_CFG_ORG}: ${KERNELSRCTAR}
>  	cd ${KERNEL_SRC}; patch -p1 < ../kvm-dynamic-halt-polling-disable-default.patch
>  	cd ${KERNEL_SRC}; patch -p1 < ../CVE-2016-4794-1-percpu-fix-synchronization-between-chunk-map_extend_.patch
>  	cd ${KERNEL_SRC}; patch -p1 < ../CVE-2016-4794-2-percpu-fix-synchronization-between-synchronous-map-e.patch
> +	cd ${KERNEL_SRC}; patch -p1 < ../CVE-2016-4470-KEYS-potential-uninitialized-variable.patch
>  	sed -i ${KERNEL_SRC}/Makefile -e 's/^EXTRAVERSION.*$$/EXTRAVERSION=${EXTRAVERSION}/'
>  	touch $@
>  
> -- 
> 2.1.4
> 
> 
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