Re: [libvirt] [CFT][PATCH 00/10] Making new mounts of proc and sysfs as safe as bind mounts (take 2)
Am 16.06.2015 um 14:31 schrieb Daniel P. Berrange: Thanks Richard / Eric for the suggested patches. I'll apply Eric's simplified patch to libvirt now, and backport it to our stable libvirt branches. Thank you Daniel! -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
Re: [libvirt] [CFT][PATCH 00/10] Making new mounts of proc and sysfs as safe as bind mounts (take 2)
On Sat, Jun 06, 2015 at 01:56:54PM -0500, Eric W. Biederman wrote:
Richard Weinberger rich...@nod.at writes:
[CC'ing libvirt-lxc folks]
Am 28.05.2015 um 23:32 schrieb Eric W. Biederman:
Richard Weinberger rich...@nod.at writes:
Am 28.05.2015 um 21:57 schrieb Eric W. Biederman:
FWIW, it breaks also libvirt-lxc:
Error: internal error: guest failed to start: Failed to re-mount
/proc/sys on /proc/sys flags=1021: Operation not permitted
Interesting. I had not anticipated a failure there? And it is failing
in remount? Oh that is interesting.
That implies that there is some flag of the original mount of /proc that
the remount of /proc/sys is clearing, and that previously
The flags specified are current rdonly,remount,bind so I expect there
are some other flags on proc that libvirt-lxc is clearing by accident
and we did not fail before because the kernel was not enforcing things.
Please see:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l933
lxcContainerMountBasicFS()
and:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l850
lxcBasicMounts
What are the mount flags in a working libvirt-lxc?
See:
test1:~ # cat /proc/self/mountinfo
149 147 0:56 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
150 149 0:56 /sys /proc/sys ro,nodev,relatime - proc proc rw
If you need more info, please let me know. :-)
Oh interesting I had not realized libvirt-lxc had grown an unprivileged
mode using user namespaces.
This does appear to be a classic remount bug, where you are not
preserving the permissions. It appears the fact that the code
failed to enforce locked permissions on the fresh mount of proc
was hiding this bug until now.
I expect what you actually want is the code below:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..f008a7484bfe 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false,
false, false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false,
false },
+{ /proc/sys, /proc/sys, NULL,
MS_BIND|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false, false },
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
Or possibly just:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..a60ccbd12bfc 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false,
false, false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false,
false },
+{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, true, false,
false },
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
As the there is little point in making /proc/sys read-only in a
user-namespace, as the permission checks are uid based and no-one should
have the global uid 0 in your container. Making mounting /proc/sys
read-only rather pointless.
Eric, using the patch below I was able to spawn a user-namespace enabled
container
using libvirt-lxc. :-)
I had to:
1. Disable the read-only mount of /proc/sys which is anyway useless in the
user-namespace case.
2. Disable the /proc/sys/net/ipv{4,6} bind mounts, this ugly hack is only
needed for the non user-namespace case.
3. Remove MS_RDONLY from the sysfs mount (For the non user-namespace case
we'd have to keep this, though).
Daniel, I'd take this as a chance to disable all the MS_RDONLY games if
user-namespace are configured.
With Eric's fixes they hurt us. And as I wrote many times before if root
within the user-namespace
is able to do nasty things in /sys and /proc that's a plain kernel bug
which needs fixing. There is no
point in mounting these read-only. Except for the case then no
user-namespace is used.
For clarity the patch below appears to be the minimal change needed to
fix this security issue.
AKA add mnt_mflags in when remounting something read-only.
/proc/sys needed to be updated so it had the proper flags to be added
back in.
I hope
Re: [libvirt] [CFT][PATCH 00/10] Making new mounts of proc and sysfs as safe as bind mounts (take 2)
Richard Weinberger rich...@nod.at writes:
[CC'ing libvirt-lxc folks]
Am 28.05.2015 um 23:32 schrieb Eric W. Biederman:
Richard Weinberger rich...@nod.at writes:
Am 28.05.2015 um 21:57 schrieb Eric W. Biederman:
FWIW, it breaks also libvirt-lxc:
Error: internal error: guest failed to start: Failed to re-mount
/proc/sys on /proc/sys flags=1021: Operation not permitted
Interesting. I had not anticipated a failure there? And it is failing
in remount? Oh that is interesting.
That implies that there is some flag of the original mount of /proc that
the remount of /proc/sys is clearing, and that previously
The flags specified are current rdonly,remount,bind so I expect there
are some other flags on proc that libvirt-lxc is clearing by accident
and we did not fail before because the kernel was not enforcing things.
Please see:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l933
lxcContainerMountBasicFS()
and:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l850
lxcBasicMounts
What are the mount flags in a working libvirt-lxc?
See:
test1:~ # cat /proc/self/mountinfo
149 147 0:56 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
150 149 0:56 /sys /proc/sys ro,nodev,relatime - proc proc rw
If you need more info, please let me know. :-)
Oh interesting I had not realized libvirt-lxc had grown an unprivileged
mode using user namespaces.
This does appear to be a classic remount bug, where you are not
preserving the permissions. It appears the fact that the code
failed to enforce locked permissions on the fresh mount of proc
was hiding this bug until now.
I expect what you actually want is the code below:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..f008a7484bfe 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false,
false },
+{ /proc/sys, /proc/sys, NULL,
MS_BIND|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false, false },
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
Or possibly just:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..a60ccbd12bfc 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false,
false },
+{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, true, false, false
},
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
As the there is little point in making /proc/sys read-only in a
user-namespace, as the permission checks are uid based and no-one should
have the global uid 0 in your container. Making mounting /proc/sys
read-only rather pointless.
Eric, using the patch below I was able to spawn a user-namespace enabled
container
using libvirt-lxc. :-)
I had to:
1. Disable the read-only mount of /proc/sys which is anyway useless in the
user-namespace case.
2. Disable the /proc/sys/net/ipv{4,6} bind mounts, this ugly hack is only
needed for the non user-namespace case.
3. Remove MS_RDONLY from the sysfs mount (For the non user-namespace case
we'd have to keep this, though).
Daniel, I'd take this as a chance to disable all the MS_RDONLY games if
user-namespace are configured.
With Eric's fixes they hurt us. And as I wrote many times before if root
within the user-namespace
is able to do nasty things in /sys and /proc that's a plain kernel bug which
needs fixing. There is no
point in mounting these read-only. Except for the case then no user-namespace
is used.
For clarity the patch below appears to be the minimal change needed to
fix this security issue.
AKA add mnt_mflags in when remounting something read-only.
/proc/sys needed to be updated so it had the proper flags to be added
back in.
I hope this helps.
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..11e9514e0761 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7
Re: [libvirt] [CFT][PATCH 00/10] Making new mounts of proc and sysfs as safe as bind mounts (take 2)
[CC'ing libvirt-lxc folks]
Am 28.05.2015 um 23:32 schrieb Eric W. Biederman:
Richard Weinberger rich...@nod.at writes:
Am 28.05.2015 um 21:57 schrieb Eric W. Biederman:
FWIW, it breaks also libvirt-lxc:
Error: internal error: guest failed to start: Failed to re-mount /proc/sys
on /proc/sys flags=1021: Operation not permitted
Interesting. I had not anticipated a failure there? And it is failing
in remount? Oh that is interesting.
That implies that there is some flag of the original mount of /proc that
the remount of /proc/sys is clearing, and that previously
The flags specified are current rdonly,remount,bind so I expect there
are some other flags on proc that libvirt-lxc is clearing by accident
and we did not fail before because the kernel was not enforcing things.
Please see:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l933
lxcContainerMountBasicFS()
and:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l850
lxcBasicMounts
What are the mount flags in a working libvirt-lxc?
See:
test1:~ # cat /proc/self/mountinfo
149 147 0:56 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
150 149 0:56 /sys /proc/sys ro,nodev,relatime - proc proc rw
If you need more info, please let me know. :-)
Oh interesting I had not realized libvirt-lxc had grown an unprivileged
mode using user namespaces.
This does appear to be a classic remount bug, where you are not
preserving the permissions. It appears the fact that the code
failed to enforce locked permissions on the fresh mount of proc
was hiding this bug until now.
I expect what you actually want is the code below:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..f008a7484bfe 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false, false
},
+{ /proc/sys, /proc/sys, NULL,
MS_BIND|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false, false },
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
Or possibly just:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..a60ccbd12bfc 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false, false
},
+{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, true, false, false
},
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
As the there is little point in making /proc/sys read-only in a
user-namespace, as the permission checks are uid based and no-one should
have the global uid 0 in your container. Making mounting /proc/sys
read-only rather pointless.
Eric, using the patch below I was able to spawn a user-namespace enabled
container
using libvirt-lxc. :-)
I had to:
1. Disable the read-only mount of /proc/sys which is anyway useless in the
user-namespace case.
2. Disable the /proc/sys/net/ipv{4,6} bind mounts, this ugly hack is only
needed for the non user-namespace case.
3. Remove MS_RDONLY from the sysfs mount (For the non user-namespace case we'd
have to keep this, though).
Daniel, I'd take this as a chance to disable all the MS_RDONLY games if
user-namespace are configured.
With Eric's fixes they hurt us. And as I wrote many times before if root within
the user-namespace
is able to do nasty things in /sys and /proc that's a plain kernel bug which
needs fixing. There is no
point in mounting these read-only. Except for the case then no user-namespace
is used.
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c..497e05f 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,10 +850,10 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false, false },
-{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
-
Re: [libvirt] [CFT][PATCH 00/10] Making new mounts of proc and sysfs as safe as bind mounts (take 2)
Richard Weinberger rich...@nod.at writes:
[CC'ing libvirt-lxc folks]
Am 28.05.2015 um 23:32 schrieb Eric W. Biederman:
Richard Weinberger rich...@nod.at writes:
Am 28.05.2015 um 21:57 schrieb Eric W. Biederman:
FWIW, it breaks also libvirt-lxc:
Error: internal error: guest failed to start: Failed to re-mount
/proc/sys on /proc/sys flags=1021: Operation not permitted
Interesting. I had not anticipated a failure there? And it is failing
in remount? Oh that is interesting.
That implies that there is some flag of the original mount of /proc that
the remount of /proc/sys is clearing, and that previously
The flags specified are current rdonly,remount,bind so I expect there
are some other flags on proc that libvirt-lxc is clearing by accident
and we did not fail before because the kernel was not enforcing things.
Please see:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l933
lxcContainerMountBasicFS()
and:
http://libvirt.org/git/?p=libvirt.git;a=blob;f=src/lxc/lxc_container.c;h=9a9ae5c2aaf0f90ff472f24fda43c077b44998c7;hb=HEAD#l850
lxcBasicMounts
What are the mount flags in a working libvirt-lxc?
See:
test1:~ # cat /proc/self/mountinfo
149 147 0:56 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
150 149 0:56 /sys /proc/sys ro,nodev,relatime - proc proc rw
If you need more info, please let me know. :-)
Oh interesting I had not realized libvirt-lxc had grown an unprivileged
mode using user namespaces.
This does appear to be a classic remount bug, where you are not
preserving the permissions. It appears the fact that the code
failed to enforce locked permissions on the fresh mount of proc
was hiding this bug until now.
I expect what you actually want is the code below:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..f008a7484bfe 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false,
false },
+{ /proc/sys, /proc/sys, NULL,
MS_BIND|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false, false, false },
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
Or possibly just:
diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 9a9ae5c2aaf0..a60ccbd12bfc 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -850,7 +850,7 @@ typedef struct {
static const virLXCBasicMountInfo lxcBasicMounts[] = {
{ proc, /proc, proc, MS_NOSUID|MS_NOEXEC|MS_NODEV, false, false,
false },
-{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, false, false,
false },
+{ /proc/sys, /proc/sys, NULL, MS_BIND|MS_RDONLY, true, false, false
},
{ /.oldroot/proc/sys/net/ipv4, /proc/sys/net/ipv4, NULL, MS_BIND,
false, false, true },
{ /.oldroot/proc/sys/net/ipv6, /proc/sys/net/ipv6, NULL, MS_BIND,
false, false, true },
{ sysfs, /sys, sysfs, MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY,
false, false, false },
As the there is little point in making /proc/sys read-only in a
user-namespace, as the permission checks are uid based and no-one should
have the global uid 0 in your container. Making mounting /proc/sys
read-only rather pointless.
Eric, using the patch below I was able to spawn a user-namespace enabled
container
using libvirt-lxc. :-)
I am glad.
I am trying to figure out which set of changes were necessary vs just
nice to have, to inform that part of the conversation that is asking is
there a way we can avoid breaking userspace for this security fix.
I had to:
1. Disable the read-only mount of /proc/sys which is anyway useless in
the user-namespace case.
It is likely worth addressing the libvirt-lxc MS_REMOUNT code as it does
not preserve any mount flags, or even have the capability to try.
if (bindOverReadonly
mount(mnt_src, mnt-dst, NULL,
MS_BIND|MS_REMOUNT|MS_RDONLY, NULL) 0) {
virReportSystemError(errno,
_(Failed to re-mount %s on %s flags=%x),
mnt_src, mnt-dst,
MS_BIND|MS_REMOUNT|MS_RDONLY);
goto cleanup;
}
Aka the flags during remount are hard coded (which is buggy).
So I believe even without the use of user-namespaces this code does the
wrong thing.
Likely statvfs needs to be called to get the existing mount flags and
those should be applied during remount or possibly just the mount flags
from the
