Revision aeb309b81c6bada783c3695528a3e10748e97285 authored by Huang Ying on 12 July 2019, 03:55:44 UTC, committed by Linus Torvalds on 12 July 2019, 18:05:43 UTC
Via commit 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks"),
after swapoff, the address_space associated with the swap device will be
freed. So swap_address_space() users which touch the address_space need
some kind of mechanism to prevent the address_space from being freed
during accessing.
When mincore processes an unmapped range for swapped shmem pages, it
doesn't hold the lock to prevent swap device from being swapped off. So
the following race is possible:
CPU1 CPU2
do_mincore() swapoff()
walk_page_range()
mincore_unmapped_range()
__mincore_unmapped_range
mincore_page
as = swap_address_space()
... exit_swap_address_space()
... kvfree(spaces)
find_get_page(as)
The address space may be accessed after being freed.
To fix the race, get_swap_device()/put_swap_device() is used to enclose
find_get_page() to check whether the swap entry is valid and prevent the
swap device from being swapoff during accessing.
Link: http://lkml.kernel.org/r/20190611020510.28251-1-ying.huang@intel.com
Fixes: 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks")
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 4efaceb
digsig.txt
==================================
Digital Signature Verification API
==================================
:Author: Dmitry Kasatkin
:Date: 06.10.2011
.. CONTENTS
1. Introduction
2. API
3. User-space utilities
Introduction
============
Digital signature verification API provides a method to verify digital signature.
Currently digital signatures are used by the IMA/EVM integrity protection subsystem.
Digital signature verification is implemented using cut-down kernel port of
GnuPG multi-precision integers (MPI) library. The kernel port provides
memory allocation errors handling, has been refactored according to kernel
coding style, and checkpatch.pl reported errors and warnings have been fixed.
Public key and signature consist of header and MPIs::
struct pubkey_hdr {
uint8_t version; /* key format version */
time_t timestamp; /* key made, always 0 for now */
uint8_t algo;
uint8_t nmpi;
char mpi[0];
} __packed;
struct signature_hdr {
uint8_t version; /* signature format version */
time_t timestamp; /* signature made */
uint8_t algo;
uint8_t hash;
uint8_t keyid[8];
uint8_t nmpi;
char mpi[0];
} __packed;
keyid equals to SHA1[12-19] over the total key content.
Signature header is used as an input to generate a signature.
Such approach insures that key or signature header could not be changed.
It protects timestamp from been changed and can be used for rollback
protection.
API
===
API currently includes only 1 function::
digsig_verify() - digital signature verification with public key
/**
* digsig_verify() - digital signature verification with public key
* @keyring: keyring to search key in
* @sig: digital signature
* @sigen: length of the signature
* @data: data
* @datalen: length of the data
* @return: 0 on success, -EINVAL otherwise
*
* Verifies data integrity against digital signature.
* Currently only RSA is supported.
* Normally hash of the content is used as a data for this function.
*
*/
int digsig_verify(struct key *keyring, const char *sig, int siglen,
const char *data, int datalen);
User-space utilities
====================
The signing and key management utilities evm-utils provide functionality
to generate signatures, to load keys into the kernel keyring.
Keys can be in PEM or converted to the kernel format.
When the key is added to the kernel keyring, the keyid defines the name
of the key: 5D2B05FC633EE3E8 in the example bellow.
Here is example output of the keyctl utility::
$ keyctl show
Session Keyring
-3 --alswrv 0 0 keyring: _ses
603976250 --alswrv 0 -1 \_ keyring: _uid.0
817777377 --alswrv 0 0 \_ user: kmk
891974900 --alswrv 0 0 \_ encrypted: evm-key
170323636 --alswrv 0 0 \_ keyring: _module
548221616 --alswrv 0 0 \_ keyring: _ima
128198054 --alswrv 0 0 \_ keyring: _evm
$ keyctl list 128198054
1 key in keyring:
620789745: --alswrv 0 0 user: 5D2B05FC633EE3E8
Computing file changes ...
