linux/security/keys/process_keys.c, branch v3.12.14

keys: fix race with concurrent install_user_keyrings()

2013-03-12T05:44:31Z

This fixes CVE-2013-1792. There is a race in install_user_keyrings() that can cause a NULL pointer dereference when called concurrently for the same user if the uid and uid-session keyrings are not yet created. It might be possible for an unprivileged user to trigger this by calling keyctl() from userspace in parallel immediately after logging in. Assume that we have two threads both executing lookup_user_key(), both looking for KEY_SPEC_USER_SESSION_KEYRING. THREAD A THREAD B =============================== =============================== ==>call install_user_keyrings(); if (!cred->user->session_keyring) ==>call install_user_keyrings() ... user->uid_keyring = uid_keyring; if (user->uid_keyring) return 0; <== key = cred->user->session_keyring [== NULL] user->session_keyring = session_keyring; atomic_inc(&key->usage); [oops] At the point thread A dereferences cred->user->session_keyring, thread B hasn't updated user->session_keyring yet, but thread A assumes it is populated because install_user_keyrings() returned ok. The race window is really small but can be exploited if, for example, thread B is interrupted or preempted after initializing uid_keyring, but before doing setting session_keyring. This couldn't be reproduced on a stock kernel. However, after placing systemtap probe on 'user->session_keyring = session_keyring;' that introduced some delay, the kernel could be crashed reliably. Fix this by checking both pointers before deciding whether to return. Alternatively, the test could be done away with entirely as it is checked inside the mutex - but since the mutex is global, that may not be the best way. Signed-off-by: David Howells Reported-by: Mateusz Guzik Cc: Signed-off-by: Andrew Morton Signed-off-by: James Morris

userns: Stop oopsing in key_change_session_keyring

2013-03-04T03:35:38Z

Dave Jones writes: > Just hit this on Linus' current tree. > > [ 89.621770] BUG: unable to handle kernel NULL pointer dereference at 00000000000000c8 > [ 89.623111] IP: [] commit_creds+0x250/0x2f0 > [ 89.624062] PGD 122bfd067 PUD 122bfe067 PMD 0 > [ 89.624901] Oops: 0000 [#1] PREEMPT SMP > [ 89.625678] Modules linked in: caif_socket caif netrom bridge hidp 8021q garp stp mrp rose llc2 af_rxrpc phonet af_key binfmt_misc bnep l2tp_ppp can_bcm l2tp_core pppoe pppox can_raw scsi_transport_iscsi ppp_generic slhc nfnetlink can ipt_ULOG ax25 decnet irda nfc rds x25 crc_ccitt appletalk atm ipx p8023 psnap p8022 llc lockd sunrpc ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_conntrack nf_conntrack ip6table_filter ip6_tables btusb bluetooth snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_pcm vhost_net snd_page_alloc snd_timer tun macvtap usb_debug snd rfkill microcode macvlan edac_core pcspkr serio_raw kvm_amd soundcore kvm r8169 mii > [ 89.637846] CPU 2 > [ 89.638175] Pid: 782, comm: trinity-main Not tainted 3.8.0+ #63 Gigabyte Technology Co., Ltd. GA-MA78GM-S2H/GA-MA78GM-S2H > [ 89.639850] RIP: 0010:[] [] commit_creds+0x250/0x2f0 > [ 89.641161] RSP: 0018:ffff880115657eb8 EFLAGS: 00010207 > [ 89.641984] RAX: 00000000000003e8 RBX: ffff88012688b000 RCX: 0000000000000000 > [ 89.643069] RDX: 0000000000000000 RSI: ffffffff81c32960 RDI: ffff880105839600 > [ 89.644167] RBP: ffff880115657ed8 R08: 0000000000000000 R09: 0000000000000000 > [ 89.645254] R10: 0000000000000001 R11: 0000000000000246 R12: ffff880105839600 > [ 89.646340] R13: ffff88011beea490 R14: ffff88011beea490 R15: 0000000000000000 > [ 89.647431] FS: 00007f3ac063b740(0000) GS:ffff88012b200000(0000) knlGS:0000000000000000 > [ 89.648660] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > [ 89.649548] CR2: 00000000000000c8 CR3: 0000000122bfc000 CR4: 00000000000007e0 > [ 89.650635] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 89.651723] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > [ 89.652812] Process trinity-main (pid: 782, threadinfo ffff880115656000, task ffff88011beea490) > [ 89.654128] Stack: > [ 89.654433] 0000000000000000 ffff8801058396a0 ffff880105839600 ffff88011beeaa78 > [ 89.655769] ffff880115657ef8 ffffffff812c7d9b ffffffff82079be0 0000000000000000 > [ 89.657073] ffff880115657f28 ffffffff8106c665 0000000000000002 ffff880115657f58 > [ 89.658399] Call Trace: > [ 89.658822] [] key_change_session_keyring+0xfb/0x140 > [ 89.659845] [] task_work_run+0xa5/0xd0 > [ 89.660698] [] do_notify_resume+0x71/0xb0 > [ 89.661581] [] int_signal+0x12/0x17 > [ 89.662385] Code: 24 90 00 00 00 48 8b b3 90 00 00 00 49 8b 4c 24 40 48 39 f2 75 08 e9 83 00 00 00 48 89 ca 48 81 fa 60 29 c3 81 0f 84 41 fe ff ff <48> 8b 8a c8 00 00 00 48 39 ce 75 e4 3b 82 d0 00 00 00 0f 84 4b > [ 89.667778] RIP [] commit_creds+0x250/0x2f0 > [ 89.668733] RSP > [ 89.669301] CR2: 00000000000000c8 > > My fastest trinity induced oops yet! > > > Appears to be.. > > if ((set_ns == subset_ns->parent) && > 850: 48 8b 8a c8 00 00 00 mov 0xc8(%rdx),%rcx > > from the inlined cred_cap_issubset By historical accident we have been reading trying to set new->user_ns from new->user_ns. Which is totally silly as new->user_ns is NULL (as is every other field in new except session_keyring at that point). The intent is clearly to copy all of the fields from old to new so copy old->user_ns into into new->user_ns. Cc: stable@vger.kernel.org Reported-by: Dave Jones Tested-by: Dave Jones Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman"

KEYS: Revert one application of "Fix unreachable code" patch

2013-02-21T15:56:25Z

A patch to fix some unreachable code in search_my_process_keyrings() got applied twice by two different routes upstream as commits e67eab39bee2 and b010520ab3d2 (both "fix unreachable code"). Unfortunately, the second application removed something it shouldn't have and this wasn't detected by GIT. This is due to the patch not having sufficient lines of context to distinguish the two places of application. The effect of this is relatively minor: inside the kernel, the keyring search routines may search multiple keyrings and then prioritise the errors if no keys or negative keys are found in any of them. With the extra deletion, the presence of a negative key in the thread keyring (causing ENOKEY) is incorrectly overridden by an error searching the process keyring. So revert the second application of the patch. Signed-off-by: David Howells Cc: Jiri Kosina Cc: Andrew Morton Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds

keys: fix unreachable code

2012-12-21T01:40:21Z

We set ret to NULL then test it. Remove the bogus test Signed-off-by: Alan Cox Signed-off-by: David Howells Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

2012-12-16T23:40:50Z

Pull security subsystem updates from James Morris: "A quiet cycle for the security subsystem with just a few maintenance updates." * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: Smack: create a sysfs mount point for smackfs Smack: use select not depends in Kconfig Yama: remove locking from delete path Yama: add RCU to drop read locking drivers/char/tpm: remove tasklet and cleanup KEYS: Use keyring_alloc() to create special keyrings KEYS: Reduce initial permissions on keys KEYS: Make the session and process keyrings per-thread seccomp: Make syscall skipping and nr changes more consistent key: Fix resource leak keys: Fix unreachable code KEYS: Add payload preparsing opportunity prior to key instantiate or update

Merge branch 'master' into for-next

2012-10-28T18:29:19Z

Sync up with Linus' tree to be able to apply Cesar's patch against newer version of the code. Signed-off-by: Jiri Kosina

keys: Fix unreachable code

2012-10-25T16:00:27Z

We set ret to NULL then test it. Remove the bogus test Signed-off-by: Alan Cox Signed-off-by: Jiri Kosina

KEYS: Reduce initial permissions on keys

2012-10-02T18:24:56Z

Reduce the initial permissions on new keys to grant the possessor everything, view permission only to the user (so the keys can be seen in /proc/keys) and nothing else. This gives the creator a chance to adjust the permissions mask before other processes can access the new key or create a link to it. To aid with this, keyring_alloc() now takes a permission argument rather than setting the permissions itself. The following permissions are now set: (1) The user and user-session keyrings grant the user that owns them full permissions and grant a possessor everything bar SETATTR. (2) The process and thread keyrings grant the possessor full permissions but only grant the user VIEW. This permits the user to see them in /proc/keys, but not to do anything with them. (3) Anonymous session keyrings grant the possessor full permissions, but only grant the user VIEW and READ. This means that the user can see them in /proc/keys and can list them, but nothing else. Possibly READ shouldn't be provided either. (4) Named session keyrings grant everything an anonymous session keyring does, plus they grant the user LINK permission. The whole point of named session keyrings is that others can also subscribe to them. Possibly this should be a separate permission to LINK. (5) The temporary session keyring created by call_sbin_request_key() gets the same permissions as an anonymous session keyring. (6) Keys created by add_key() get VIEW, SEARCH, LINK and SETATTR for the possessor, plus READ and/or WRITE if the key type supports them. The used only gets VIEW now. (7) Keys created by request_key() now get the same as those created by add_key(). Reported-by: Lennart Poettering Reported-by: Stef Walter Signed-off-by: David Howells

KEYS: Make the session and process keyrings per-thread

2012-10-02T18:24:29Z

Make the session keyring per-thread rather than per-process, but still inherited from the parent thread to solve a problem with PAM and gdm. The problem is that join_session_keyring() will reject attempts to change the session keyring of a multithreaded program but gdm is now multithreaded before it gets to the point of starting PAM and running pam_keyinit to create the session keyring. See: https://bugs.freedesktop.org/show_bug.cgi?id=49211 The reason that join_session_keyring() will only change the session keyring under a single-threaded environment is that it's hard to alter the other thread's credentials to effect the change in a multi-threaded program. The problems are such as: (1) How to prevent two threads both running join_session_keyring() from racing. (2) Another thread's credentials may not be modified directly by this process. (3) The number of threads is uncertain whilst we're not holding the appropriate spinlock, making preallocation slightly tricky. (4) We could use TIF_NOTIFY_RESUME and key_replace_session_keyring() to get another thread to replace its keyring, but that means preallocating for each thread. A reasonable way around this is to make the session keyring per-thread rather than per-process and just document that if you want a common session keyring, you must get it before you spawn any threads - which is the current situation anyway. Whilst we're at it, we can the process keyring behave in the same way. This means we can clean up some of the ickyness in the creds code. Basically, after this patch, the session, process and thread keyrings are about inheritance rules only and not about sharing changes of keyring. Reported-by: Mantas M. Signed-off-by: David Howells Tested-by: Ray Strode

keys: Fix unreachable code

2012-09-28T11:20:02Z

We set ret to NULL then test it. Remove the bogus test Signed-off-by: Alan Cox Signed-off-by: David Howells