Re: [PATCH v2] general protection fault in sock_has_perm
On Thu, Feb 01, 2018 at 07:37:04AM -0800, Mark Salyzyn wrote: > In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket > flag") and all the associated infrastructure changes to take advantage > of a RCU grace period before freeing, there is a heightened > possibility that a security check is performed while an ill-timed > setsockopt call races in from user space. It then is prudent to null > check sk_security, and if the case, reject the permissions. > > Because of the nature of this problem, hard to duplicate, no clear > path, this patch is a simplified band-aid for stable trees lacking the > infrastructure for the series of commits leading up to providing a > suitable RCU grace period. This adjustment is orthogonal to > infrastructure improvements that may nullify the needed check, but > could be added as good code hygiene in all trees. > > general protection fault: [#1] PREEMPT SMP KASAN > CPU: 1 PID: 14233 Comm: syz-executor2 Not tainted 4.4.112-g5f6325b #28 > task: 8801d1095f00 task.stack: 8800b595 > RIP: 0010:[] [] > sock_has_perm+0x1fe/0x3e0 security/selinux/hooks.c:4069 > RSP: 0018:8800b5957ce0 EFLAGS: 00010202 > RAX: dc00 RBX: 110016b2af9f RCX: 81b69b51 > RDX: 0002 RSI: RDI: 0010 > RBP: 8800b5957de0 R08: 0001 R09: 0001 > R10: R11: 110016b2af68 R12: 8800b5957db8 > R13: R14: 8800b7259f40 R15: 00d7 > FS: 7f72f5ae2700() GS:8801db30() knlGS: > CS: 0010 DS: ES: CR0: 80050033 > CR2: 00a2fa38 CR3: 0001d798 CR4: 00160670 > DR0: DR1: DR2: > DR3: DR6: fffe0ff0 DR7: 0400 > Stack: > 81b69a1f 8800b5957d58 8000b5957d30 41b58ab3 > 83fc82f2 81b69980 0246 8801d1096770 > 8801d3165668 8157844b 8801d1095f00 > 8801 > Call Trace: > [] selinux_socket_setsockopt+0x4d/0x80 > security/selinux/hooks.c:4338 > [] security_socket_setsockopt+0x7d/0xb0 > security/security.c:1257 > [] SYSC_setsockopt net/socket.c:1757 [inline] > [] SyS_setsockopt+0xe8/0x250 net/socket.c:1746 > [] entry_SYSCALL_64_fastpath+0x16/0x92 > Code: c2 42 9b b6 81 be 01 00 00 00 48 c7 c7 a0 cb 2b 84 e8 > f7 2f 6d ff 49 8d 7d 10 48 b8 00 00 00 00 00 fc ff df 48 89 > fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 83 01 00 > 00 41 8b 75 10 31 > RIP [] sock_has_perm+0x1fe/0x3e0 > security/selinux/hooks.c:4069 > RSP > ---[ end trace 7b5aaf788fef6174 ]--- > > Signed-off-by: Mark Salyzyn > Signed-off-by: Paul Moore > Signed-off-by: Greg KH > Cc: Eric Dumazet > Cc: Stephen Smalley > Cc: selinux@tycho.nsa.gov > Cc: linux-security-mod...@vger.kernel.org > Cc: Eric Paris > Cc: Serge E. Hallyn > Cc: stable # 3.18, 4.4 > Cc: linux-ker...@vger.kernel.org > --- > v2: return -EFAULT for null sk_security instead of 0 Now queued up, thanks. greg k-h
Re: [PATCH v2] general protection fault in sock_has_perm
On 02/01/2018 09:02 AM, Stephen Smalley wrote: On Thu, 2018-02-01 at 08:20 -0800, Mark Salyzyn wrote: On 02/01/2018 08:00 AM, Paul Moore wrote: On Thu, Feb 1, 2018 at 10:37 AM, Mark Salyzyn wrote: In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket flag") and all the associated infrastructure changes to take advantage of a RCU grace period before freeing, there is a heightened possibility that a security check is performed while an ill-timed setsockopt call races in from user space. It then is prudent to null check sk_security, and if the case, reject the permissions. . . . ---[ end trace 7b5aaf788fef6174 ]--- Signed-off-by: Mark Salyzyn Signed-off-by: Paul Moore No, in the previous thread I gave my ack, not my sign-off; please be more careful in the future. It may seem silly, especially in this particular case, but it is an important distinction when things like the DCO are concerned. Anyway, here is my ack again. Acked-by: Paul Moore Ok, both Greg KH and yours should be considered Acked-By. Been overstepping this boundary for _years_. AFAIK Signed-off-by is still pending from Stephen Smalley before this can roll in. Lesson lurned No, Paul's Acked-by is sufficient, and at most, I would only add another Acked-by or Reviewed-by, not a Signed-off-by. Signed-off-by is only needed when one had something to do with the writing of the patch or was in the path by which it was merged. I don't object to this patch but I have a hard time adding another ack because I don't truly understand the root cause or how this fixes it. Let's say sk_prot_free() calls security_sk_free() calls selinux_sk_free_security() which sets sk->sk_security to NULL, and then we proceed to free the sksec and then sk_prot_free() frees the sk itself. Now another sock is allocated (or perhaps a different object altogether), reuses that memory, and whatever sk->sk_security happens to contain is set to non-NULL. We'll just blithely proceed past your check and who knows what will happen from that point onward. The way I read this is this is part of an RCU operation. Multiple readers are holding on to the object, but as soon as a new writer comes in it _immediately_ frees the sk_security of the 'old' reader copies in order to make the 'new' writer copy. Any pending readers continue operations until they get tripped on the too aggressively released NULL sk_security reference. Commits came in between 4.4 and 4.9 (eduma...@google.com) to restructure and fix this and add the appropriate RCU grace period to the 'old' reader copies for the sk_security resource so that it would be freed after all the readers had exited. Problem goes away. My proposal will break any 'old' readers by blocking their access during the transition rather than panic the kernel. New readers coming in after the writer will progress fine. This is not a 'bug' in the security layer, this is a bandaid to the security layer regarding the bad behavior of the callers. I have not analyzed the code enough to 100% prove my assertion above, in part because I can not duplicate the problem w/o kasan+fuzzing, so still treat this as a hunch. -- Mark
Re: [PATCH v2] general protection fault in sock_has_perm
On Thu, Feb 01, 2018 at 08:20:13AM -0800, Mark Salyzyn wrote: > On 02/01/2018 08:00 AM, Paul Moore wrote: > > On Thu, Feb 1, 2018 at 10:37 AM, Mark Salyzyn wrote: > > > In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket > > > flag") and all the associated infrastructure changes to take advantage > > > of a RCU grace period before freeing, there is a heightened > > > possibility that a security check is performed while an ill-timed > > > setsockopt call races in from user space. It then is prudent to null > > > check sk_security, and if the case, reject the permissions. > > > > > > . . . > > > ---[ end trace 7b5aaf788fef6174 ]--- > > > > > > Signed-off-by: Mark Salyzyn > > > Signed-off-by: Paul Moore > > No, in the previous thread I gave my ack, not my sign-off; please be > > more careful in the future. It may seem silly, especially in this > > particular case, but it is an important distinction when things like > > the DCO are concerned. > > > > Anyway, here is my ack again. > > > > Acked-by: Paul Moore > > > Ok, both Greg KH and yours should be considered Acked-By. Been overstepping > this boundary for _years_. AFAIK Signed-off-by is still pending from Stephen > Smalley before this can roll in. An ack is all I need here, or I can just rely on Paul's :) I'll edit up Paul's when I apply this. thanks, greg k-h
Re: [PATCH v2] general protection fault in sock_has_perm
On Thu, 2018-02-01 at 08:20 -0800, Mark Salyzyn wrote: > On 02/01/2018 08:00 AM, Paul Moore wrote: > > On Thu, Feb 1, 2018 at 10:37 AM, Mark Salyzyn > > wrote: > > > In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE > > > socket > > > flag") and all the associated infrastructure changes to take > > > advantage > > > of a RCU grace period before freeing, there is a heightened > > > possibility that a security check is performed while an ill-timed > > > setsockopt call races in from user space. It then is prudent to > > > null > > > check sk_security, and if the case, reject the permissions. > > > > > > . . . > > > ---[ end trace 7b5aaf788fef6174 ]--- > > > > > > Signed-off-by: Mark Salyzyn > > > Signed-off-by: Paul Moore > > > > No, in the previous thread I gave my ack, not my sign-off; please > > be > > more careful in the future. It may seem silly, especially in this > > particular case, but it is an important distinction when things > > like > > the DCO are concerned. > > > > Anyway, here is my ack again. > > > > Acked-by: Paul Moore > > > > Ok, both Greg KH and yours should be considered Acked-By. Been > overstepping this boundary for _years_. AFAIK Signed-off-by is still > pending from Stephen Smalley before this can roll > in. > > Lesson lurned No, Paul's Acked-by is sufficient, and at most, I would only add another Acked-by or Reviewed-by, not a Signed-off-by. Signed-off-by is only needed when one had something to do with the writing of the patch or was in the path by which it was merged. I don't object to this patch but I have a hard time adding another ack because I don't truly understand the root cause or how this fixes it. Let's say sk_prot_free() calls security_sk_free() calls selinux_sk_free_security() which sets sk->sk_security to NULL, and then we proceed to free the sksec and then sk_prot_free() frees the sk itself. Now another sock is allocated (or perhaps a different object altogether), reuses that memory, and whatever sk->sk_security happens to contain is set to non-NULL. We'll just blithely proceed past your check and who knows what will happen from that point onward.
Re: [PATCH v2] general protection fault in sock_has_perm
On Thu, Feb 1, 2018 at 11:20 AM, Mark Salyzyn wrote: > On 02/01/2018 08:00 AM, Paul Moore wrote: >> >> On Thu, Feb 1, 2018 at 10:37 AM, Mark Salyzyn wrote: >>> >>> In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket >>> flag") and all the associated infrastructure changes to take advantage >>> of a RCU grace period before freeing, there is a heightened >>> possibility that a security check is performed while an ill-timed >>> setsockopt call races in from user space. It then is prudent to null >>> check sk_security, and if the case, reject the permissions. >>> >>> . . . >>> ---[ end trace 7b5aaf788fef6174 ]--- >>> >>> Signed-off-by: Mark Salyzyn >>> Signed-off-by: Paul Moore >> >> No, in the previous thread I gave my ack, not my sign-off; please be >> more careful in the future. It may seem silly, especially in this >> particular case, but it is an important distinction when things like >> the DCO are concerned. >> >> Anyway, here is my ack again. >> >> Acked-by: Paul Moore >> > Ok, both Greg KH and yours should be considered Acked-By. Been overstepping > this boundary for _years_. One more note, which I didn't realize until I hit reply and the email bounced: you used a @linuxfoundation.org email address for me which is clearly not right. I'm sure it's just a typo, but it's another thing that needs to be corrected. > AFAIK Signed-off-by is still pending from Stephen > Smalley before this can roll in. Obviously the more acks the better, but you've got mine which should be sufficient in this case. The MAINTAINER file currently lists three people for SELinux: Stephen, Eric, and myself. I'm responsible for the traditional maintainer tasks: tree management, PRs to Linus, patch review, emptying the waste bin at the end of the week, etc. Stephen maintains the deep historical knowledge and understanding that comes with developing the technology/project from it's inception many, many years ago; no matter how well I may understand SELinux, Stephen will always have me beat. Eric is basically my predecessor, having ventured off to the brave new world of containers and Kubernetes; he is listed out of respect for his contributions and also to safeguard us against the all important "bus factor", while he is not as active as he once was, he still holds a wealth of SELinux knowledge. -- paul moore www.paul-moore.com
Re: [PATCH v2] general protection fault in sock_has_perm
On 02/01/2018 08:00 AM, Paul Moore wrote: On Thu, Feb 1, 2018 at 10:37 AM, Mark Salyzyn wrote: In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket flag") and all the associated infrastructure changes to take advantage of a RCU grace period before freeing, there is a heightened possibility that a security check is performed while an ill-timed setsockopt call races in from user space. It then is prudent to null check sk_security, and if the case, reject the permissions. . . . ---[ end trace 7b5aaf788fef6174 ]--- Signed-off-by: Mark Salyzyn Signed-off-by: Paul Moore No, in the previous thread I gave my ack, not my sign-off; please be more careful in the future. It may seem silly, especially in this particular case, but it is an important distinction when things like the DCO are concerned. Anyway, here is my ack again. Acked-by: Paul Moore Ok, both Greg KH and yours should be considered Acked-By. Been overstepping this boundary for _years_. AFAIK Signed-off-by is still pending from Stephen Smalley before this can roll in. Lesson lurned -- Mark
Re: [PATCH v2] general protection fault in sock_has_perm
On Thu, Feb 1, 2018 at 10:37 AM, Mark Salyzyn wrote: > In the absence of commit a4298e4522d6 ("net: add SOCK_RCU_FREE socket > flag") and all the associated infrastructure changes to take advantage > of a RCU grace period before freeing, there is a heightened > possibility that a security check is performed while an ill-timed > setsockopt call races in from user space. It then is prudent to null > check sk_security, and if the case, reject the permissions. > > Because of the nature of this problem, hard to duplicate, no clear > path, this patch is a simplified band-aid for stable trees lacking the > infrastructure for the series of commits leading up to providing a > suitable RCU grace period. This adjustment is orthogonal to > infrastructure improvements that may nullify the needed check, but > could be added as good code hygiene in all trees. > > general protection fault: [#1] PREEMPT SMP KASAN > CPU: 1 PID: 14233 Comm: syz-executor2 Not tainted 4.4.112-g5f6325b #28 > task: 8801d1095f00 task.stack: 8800b595 > RIP: 0010:[] [] > sock_has_perm+0x1fe/0x3e0 security/selinux/hooks.c:4069 > RSP: 0018:8800b5957ce0 EFLAGS: 00010202 > RAX: dc00 RBX: 110016b2af9f RCX: 81b69b51 > RDX: 0002 RSI: RDI: 0010 > RBP: 8800b5957de0 R08: 0001 R09: 0001 > R10: R11: 110016b2af68 R12: 8800b5957db8 > R13: R14: 8800b7259f40 R15: 00d7 > FS: 7f72f5ae2700() GS:8801db30() knlGS: > CS: 0010 DS: ES: CR0: 80050033 > CR2: 00a2fa38 CR3: 0001d798 CR4: 00160670 > DR0: DR1: DR2: > DR3: DR6: fffe0ff0 DR7: 0400 > Stack: > 81b69a1f 8800b5957d58 8000b5957d30 41b58ab3 > 83fc82f2 81b69980 0246 8801d1096770 > 8801d3165668 8157844b 8801d1095f00 > 8801 > Call Trace: > [] selinux_socket_setsockopt+0x4d/0x80 > security/selinux/hooks.c:4338 > [] security_socket_setsockopt+0x7d/0xb0 > security/security.c:1257 > [] SYSC_setsockopt net/socket.c:1757 [inline] > [] SyS_setsockopt+0xe8/0x250 net/socket.c:1746 > [] entry_SYSCALL_64_fastpath+0x16/0x92 > Code: c2 42 9b b6 81 be 01 00 00 00 48 c7 c7 a0 cb 2b 84 e8 > f7 2f 6d ff 49 8d 7d 10 48 b8 00 00 00 00 00 fc ff df 48 89 > fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 83 01 00 > 00 41 8b 75 10 31 > RIP [] sock_has_perm+0x1fe/0x3e0 > security/selinux/hooks.c:4069 > RSP > ---[ end trace 7b5aaf788fef6174 ]--- > > Signed-off-by: Mark Salyzyn > Signed-off-by: Paul Moore No, in the previous thread I gave my ack, not my sign-off; please be more careful in the future. It may seem silly, especially in this particular case, but it is an important distinction when things like the DCO are concerned. Anyway, here is my ack again. Acked-by: Paul Moore > Signed-off-by: Greg KH > Cc: Eric Dumazet > Cc: Stephen Smalley > Cc: selinux@tycho.nsa.gov > Cc: linux-security-mod...@vger.kernel.org > Cc: Eric Paris > Cc: Serge E. Hallyn > Cc: stable # 3.18, 4.4 > Cc: linux-ker...@vger.kernel.org > --- > v2: return -EFAULT for null sk_security instead of 0 > > security/selinux/hooks.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 8644d864e3c1..795efa71d656 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -4342,6 +4342,8 @@ static int sock_has_perm(struct sock *sk, u32 perms) > struct common_audit_data ad; > struct lsm_network_audit net = {0,}; > > + if (!sksec) > + return -EFAULT; > if (sksec->sid == SECINITSID_KERNEL) > return 0; > > -- > 2.16.0.rc1.238.g530d649a79-goog -- paul moore www.paul-moore.com