| Message ID | 20200108162447.3347-1-sds@tycho.nsa.gov (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | Documentation,selinux: deprecate setting checkreqprot to 1 | expand |
On Wed, Jan 8, 2020 at 11:24 AM Stephen Smalley <sds@tycho.nsa.gov> wrote: > Deprecate setting the SELinux checkreqprot tunable to 1 via kernel > parameter or /sys/fs/selinux/checkreqprot. Setting it to 0 is left > intact for compatibility since Android and some Linux distributions > do so for security and treat an inability to set it as a fatal error. > Eventually setting it to 0 will become a no-op and the kernel will > stop using checkreqprot's value internally altogether. > > checkreqprot was originally introduced as a compatibility mechanism > for legacy userspace and the READ_IMPLIES_EXEC personality flag. > However, if set to 1, it weakens security by allowing mappings to be > made executable without authorization by policy. The default value > for the SECURITY_SELINUX_CHECKREQPROT_VALUE config option was changed > from 1 to 0 in commit 2a35d196c160e3 ("selinux: change > CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE default") and both Android > and Linux distributions began explicitly setting > /sys/fs/selinux/checkreqprot to 0 some time ago. > > Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov> > --- > .../ABI/obsolete/sysfs-selinux-checkreqprot | 23 +++++++++++++++++++ > .../admin-guide/kernel-parameters.txt | 1 + > MAINTAINERS | 1 + > security/selinux/Kconfig | 3 +++ > security/selinux/hooks.c | 5 +++- > security/selinux/selinuxfs.c | 8 +++++++ > 6 files changed, 40 insertions(+), 1 deletion(-) > create mode 100644 Documentation/ABI/obsolete/sysfs-selinux-checkreqprot I think this looks fine, but considering this week was the first time we really discussed this, let's hold off until after the next merge window so we get a full cycle in linux-next for folks to complain :)
On Fri, Jan 10, 2020 at 3:15 PM Paul Moore <paul@paul-moore.com> wrote: > On Wed, Jan 8, 2020 at 11:24 AM Stephen Smalley <sds@tycho.nsa.gov> wrote: > > Deprecate setting the SELinux checkreqprot tunable to 1 via kernel > > parameter or /sys/fs/selinux/checkreqprot. Setting it to 0 is left > > intact for compatibility since Android and some Linux distributions > > do so for security and treat an inability to set it as a fatal error. > > Eventually setting it to 0 will become a no-op and the kernel will > > stop using checkreqprot's value internally altogether. > > > > checkreqprot was originally introduced as a compatibility mechanism > > for legacy userspace and the READ_IMPLIES_EXEC personality flag. > > However, if set to 1, it weakens security by allowing mappings to be > > made executable without authorization by policy. The default value > > for the SECURITY_SELINUX_CHECKREQPROT_VALUE config option was changed > > from 1 to 0 in commit 2a35d196c160e3 ("selinux: change > > CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE default") and both Android > > and Linux distributions began explicitly setting > > /sys/fs/selinux/checkreqprot to 0 some time ago. > > > > Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov> > > --- > > .../ABI/obsolete/sysfs-selinux-checkreqprot | 23 +++++++++++++++++++ > > .../admin-guide/kernel-parameters.txt | 1 + > > MAINTAINERS | 1 + > > security/selinux/Kconfig | 3 +++ > > security/selinux/hooks.c | 5 +++- > > security/selinux/selinuxfs.c | 8 +++++++ > > 6 files changed, 40 insertions(+), 1 deletion(-) > > create mode 100644 Documentation/ABI/obsolete/sysfs-selinux-checkreqprot > > I think this looks fine, but considering this week was the first time > we really discussed this, let's hold off until after the next merge > window so we get a full cycle in linux-next for folks to complain :) I've queued this up in selinux/next, you'll see it in the tree once the merge window closes.
diff --git a/Documentation/ABI/obsolete/sysfs-selinux-checkreqprot b/Documentation/ABI/obsolete/sysfs-selinux-checkreqprot new file mode 100644 index 000000000000..49ed9c8fd1e5 --- /dev/null +++ b/Documentation/ABI/obsolete/sysfs-selinux-checkreqprot @@ -0,0 +1,23 @@ +What: /sys/fs/selinux/checkreqprot +Date: April 2005 (predates git) +KernelVersion: 2.6.12-rc2 (predates git) +Contact: selinux@vger.kernel.org +Description: + + The selinuxfs "checkreqprot" node allows SELinux to be configured + to check the protection requested by userspace for mmap/mprotect + calls instead of the actual protection applied by the kernel. + This was a compatibility mechanism for legacy userspace and + for the READ_IMPLIES_EXEC personality flag. However, if set to + 1, it weakens security by allowing mappings to be made executable + without authorization by policy. The default value of checkreqprot + at boot was changed starting in Linux v4.4 to 0 (i.e. check the + actual protection), and Android and Linux distributions have been + explicitly writing a "0" to /sys/fs/selinux/checkreqprot during + initialization for some time. Support for setting checkreqprot to 1 + will be removed in a future kernel release, at which point the kernel + will always cease using checkreqprot internally and will always + check the actual protections being applied upon mmap/mprotect calls. + The checkreqprot selinuxfs node will remain for backward compatibility + but will discard writes of the "0" value and will reject writes of the + "1" value when this mechanism is removed. diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index eed51293d6cf..c894ddfa1393 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -512,6 +512,7 @@ Default value is set via a kernel config option. Value can be changed at runtime via /sys/fs/selinux/checkreqprot. + Setting checkreqprot to 1 is deprecated. cio_ignore= [S390] See Documentation/s390/common_io.rst for details. diff --git a/MAINTAINERS b/MAINTAINERS index 9dc5767861b5..1af5e9e8abb5 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -14807,6 +14807,7 @@ F: security/selinux/ F: scripts/selinux/ F: Documentation/admin-guide/LSM/SELinux.rst F: Documentation/ABI/obsolete/sysfs-selinux-disable +F: Documentation/ABI/obsolete/sysfs-selinux-checkreqprot SENSABLE PHANTOM M: Jiri Slaby <jirislaby@gmail.com> diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig index 1014cb0ee956..9e921fc72538 100644 --- a/security/selinux/Kconfig +++ b/security/selinux/Kconfig @@ -88,6 +88,9 @@ config SECURITY_SELINUX_CHECKREQPROT_VALUE 'checkreqprot=' boot parameter. It may also be changed at runtime via /sys/fs/selinux/checkreqprot if authorized by policy. + WARNING: this option is deprecated and will be removed in a future + kernel release. + If you are unsure how to answer this question, answer 0. config SECURITY_SELINUX_SIDTAB_HASH_BITS diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 63a6e36abe9f..6777e04fd942 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -142,8 +142,11 @@ static int __init checkreqprot_setup(char *str) { unsigned long checkreqprot; - if (!kstrtoul(str, 0, &checkreqprot)) + if (!kstrtoul(str, 0, &checkreqprot)) { selinux_checkreqprot_boot = checkreqprot ? 1 : 0; + if (checkreqprot) + pr_warn("SELinux: checkreqprot set to 1 via kernel parameter. This is deprecated and will be rejected in a future kernel release.\n"); + } return 1; } __setup("checkreqprot=", checkreqprot_setup); diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c index 79c710911a3c..d6566adc73a6 100644 --- a/security/selinux/selinuxfs.c +++ b/security/selinux/selinuxfs.c @@ -668,6 +668,14 @@ static ssize_t sel_write_checkreqprot(struct file *file, const char __user *buf, if (sscanf(page, "%u", &new_value) != 1) goto out; + if (new_value) { + char comm[sizeof(current->comm)]; + + memcpy(comm, current->comm, sizeof(comm)); + pr_warn_once("SELinux: %s (%d) set checkreqprot to 1. This is deprecated and will be rejected in a future kernel release.\n", + comm, current->pid); + } + fsi->state->checkreqprot = new_value ? 1 : 0; length = count; out:
Deprecate setting the SELinux checkreqprot tunable to 1 via kernel parameter or /sys/fs/selinux/checkreqprot. Setting it to 0 is left intact for compatibility since Android and some Linux distributions do so for security and treat an inability to set it as a fatal error. Eventually setting it to 0 will become a no-op and the kernel will stop using checkreqprot's value internally altogether. checkreqprot was originally introduced as a compatibility mechanism for legacy userspace and the READ_IMPLIES_EXEC personality flag. However, if set to 1, it weakens security by allowing mappings to be made executable without authorization by policy. The default value for the SECURITY_SELINUX_CHECKREQPROT_VALUE config option was changed from 1 to 0 in commit 2a35d196c160e3 ("selinux: change CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE default") and both Android and Linux distributions began explicitly setting /sys/fs/selinux/checkreqprot to 0 some time ago. Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov> --- .../ABI/obsolete/sysfs-selinux-checkreqprot | 23 +++++++++++++++++++ .../admin-guide/kernel-parameters.txt | 1 + MAINTAINERS | 1 + security/selinux/Kconfig | 3 +++ security/selinux/hooks.c | 5 +++- security/selinux/selinuxfs.c | 8 +++++++ 6 files changed, 40 insertions(+), 1 deletion(-) create mode 100644 Documentation/ABI/obsolete/sysfs-selinux-checkreqprot