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linux/security
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Eric Biggers 3eab231a5b KEYS: prevent KEYCTL_READ on negative key 
commit 37863c43b2 upstream.

Because keyctl_read_key() looks up the key with no permissions
requested, it may find a negatively instantiated key.  If the key is
also possessed, we went ahead and called ->read() on the key.  But the
key payload will actually contain the ->reject_error rather than the
normal payload.  Thus, the kernel oopses trying to read the
user_key_payload from memory address (int)-ENOKEY = 0x00000000ffffff82.

Fortunately the payload data is stored inline, so it shouldn't be
possible to abuse this as an arbitrary memory read primitive...

Reproducer:
    keyctl new_session
    keyctl request2 user desc '' @s
    keyctl read $(keyctl show | awk '/user: desc/ {print $1}')

It causes a crash like the following:
     BUG: unable to handle kernel paging request at 00000000ffffff92
     IP: user_read+0x33/0xa0
     PGD 36a54067 P4D 36a54067 PUD 0
     Oops: 0000 [#1] SMP
     CPU: 0 PID: 211 Comm: keyctl Not tainted 4.14.0-rc1 #337
     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-20170228_101828-anatol 04/01/2014
     task: ffff90aa3b74c3c0 task.stack: ffff9878c0478000
     RIP: 0010:user_read+0x33/0xa0
     RSP: 0018:ffff9878c047bee8 EFLAGS: 00010246
     RAX: 0000000000000001 RBX: ffff90aa3d7da340 RCX: 0000000000000017
     RDX: 0000000000000000 RSI: 00000000ffffff82 RDI: ffff90aa3d7da340
     RBP: ffff9878c047bf00 R08: 00000024f95da94f R09: 0000000000000000
     R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
     R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
     FS:  00007f58ece69740(0000) GS:ffff90aa3e200000(0000) knlGS:0000000000000000
     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
     CR2: 00000000ffffff92 CR3: 0000000036adc001 CR4: 00000000003606f0
     Call Trace:
      keyctl_read_key+0xac/0xe0
      SyS_keyctl+0x99/0x120
      entry_SYSCALL_64_fastpath+0x1f/0xbe
     RIP: 0033:0x7f58ec787bb9
     RSP: 002b:00007ffc8d401678 EFLAGS: 00000206 ORIG_RAX: 00000000000000fa
     RAX: ffffffffffffffda RBX: 00007ffc8d402800 RCX: 00007f58ec787bb9
     RDX: 0000000000000000 RSI: 00000000174a63ac RDI: 000000000000000b
     RBP: 0000000000000004 R08: 00007ffc8d402809 R09: 0000000000000020
     R10: 0000000000000000 R11: 0000000000000206 R12: 00007ffc8d402800
     R13: 00007ffc8d4016e0 R14: 0000000000000000 R15: 0000000000000000
     Code: e5 41 55 49 89 f5 41 54 49 89 d4 53 48 89 fb e8 a4 b4 ad ff 85 c0 74 09 80 3d b9 4c 96 00 00 74 43 48 8b b3 20 01 00 00 4d 85 ed <0f> b7 5e 10 74 29 4d 85 e4 74 24 4c 39 e3 4c 89 e2 4c 89 ef 48
     RIP: user_read+0x33/0xa0 RSP: ffff9878c047bee8
     CR2: 00000000ffffff92

Fixes: 61ea0c0ba9 ("KEYS: Skip key state checks when checking for possession")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
History 2017-11-11 13:33:37 +00:00
..
apparmor sched: move no_new_privs into new atomic flags 2017-10-12 15:28:22 +01:00
integrity ima: accept previously set IMA_NEW_FILE 2017-08-26 02:14:23 +01:00
keys KEYS: prevent KEYCTL_READ on negative key 2017-11-11 13:33:37 +00:00
selinux selinux: fix double free in selinux_parse_opts_str() 2017-09-15 18:30:10 +01:00
smack sysfs: Create mountpoints with sysfs_create_mount_point 2015-08-20 18:24:03 +01:00
tomoyo get rid of pointless checks for NULL ->i_op 2014-04-01 23:19:16 -04:00
yama yama: Better permission check for ptraceme 2013-03-26 13:17:58 -07:00
capability.c Merge tag 'keys-20140314' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs into next 2014-04-14 11:42:49 +10:00
commoncap.c ptrace: use fsuid, fsgid, effective creds for fs access checks 2017-09-15 18:30:17 +01:00
device_cgroup.c device_cgroup: use css_has_online_children() instead of has_children() 2014-05-16 13:22:52 -04:00
inode.c sysfs: Create mountpoints with sysfs_create_mount_point 2015-08-20 18:24:03 +01:00
Kconfig security: select correct default LSM_MMAP_MIN_ADDR on arm on arm64 2014-02-05 14:59:14 +00:00
lsm_audit.c audit: anchor all pid references in the initial pid namespace 2014-03-20 10:11:55 -04:00
Makefile security: cleanup Makefiles to use standard syntax for specifying sub-directories 2014-02-17 11:08:04 +11:00
min_addr.c mmap_min_addr check CAP_SYS_RAWIO only for write 2010-04-23 08:56:31 +10:00
security.c vfs: Commit to never having exectuables on proc and sysfs. 2017-04-04 22:21:56 +01:00