Re: [PATCH v1 4/5] LSM: Define SELinux function to measure security state
From: Stephen Smalley <stephen.smalley.work@gmail.com>
Date: 2020-07-15 17:44:30
Also in:
linux-integrity, lkml, selinux
On Wed, Jul 15, 2020 at 11:48 AM Lakshmi Ramasubramanian [off-list ref] wrote:
SELinux configuration and policy are some of the critical data for this security module that needs to be measured. To enable this measurement SELinux needs to implement the interface function, security_state(), that the LSM can call. Define the security_state() function in SELinux to measure SELinux configuration and policy. Call this function to measure SELinux data when there is a change in the security module's state. Sample measurement of SELinux state and hash of the policy: 10 e32e...5ac3 ima-buf sha256:86e8...4594 selinux-state 656e61626c65643d313b656e666f7263696e673d303b636865636b72657170726f743d313b6e6574706565723d313b6f70656e7065726d3d313b657874736f636b636c6173733d313b616c776179736e6574776f726b3d303b6367726f75707365636c6162656c3d313b6e6e706e6f737569647472616e736974696f6e3d313b67656e66737365636c6162656c73796d6c696e6b3d303b 10 f4a7...9408 ima-buf sha256:4941...68fc selinux-policy-hash 8d1d...1834 The data for selinux-state in the above measurement is: enabled=1;enforcing=0;checkreqprot=1;netpeer=1;openperm=1;extsockclass=1;alwaysnetwork=0;cgroupseclabel=1;nnpnosuidtransition=1;genfsseclabelsymlink=0; The data for selinux-policy-hash in the above measurement is the SHA256 hash of the SELinux policy. Signed-off-by: Lakshmi Ramasubramanian <redacted> Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com> ---
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diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h index b0e02cfe3ce1..691c7e35f82a 100644 --- a/security/selinux/include/security.h +++ b/security/selinux/include/security.h@@ -222,16 +222,35 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void) return state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS]; } +static inline bool selinux_checkreqprot(void) +{ + struct selinux_state *state = &selinux_state; + + return state->checkreqprot; +}
Probably should use READ_ONCE().
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diff --git a/security/selinux/measure.c b/security/selinux/measure.c new file mode 100644 index 000000000000..b909e8e61542 --- /dev/null +++ b/security/selinux/measure.c@@ -0,0 +1,122 @@ +int selinux_security_state(void)
Let's call this selinux_measure_state() or similar. Needs a verb. And pass it a struct selinux_state * pointer argument to be measured, even though initially it will always be passed &selinux_state. The encapsulation of selinux state within selinux_state was to support multiple selinux namespaces in the future, each with their own state.
+{
+ int rc = 0;
+ int count;
+ size_t buflen;
+ int policy_hash_len;
+ char *state = NULL;
+ void *policy = NULL;
+ void *policy_hash = NULL;
+ static char *security_state_string =
+ "enabled=%d;enforcing=%d;checkreqprot=%d;" \
+ "netpeer=%d;openperm=%d;extsockclass=%d;" \
+ "alwaysnetwork=%d;cgroupseclabel=%d;" \
+ "nnpnosuidtransition=%d;genfsseclabelsymlink=%d;";Rather than hardcoding policy capability names here, I would recommend using the selinux_policycap_names[] array for the names and the selinux_state.policycap[] array for the values. Also recommend passing in a struct selinux_state * here to allow for future case where there are multiple selinux states, one per selinux namespace.
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diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c index ef0afd878bfc..0c289d13ef6a 100644 --- a/security/selinux/ss/services.c +++ b/security/selinux/ss/services.c@@ -3724,10 +3724,11 @@ int security_netlbl_sid_to_secattr(struct selinux_state *state, * security_read_policy - read the policy. * @data: binary policy data * @len: length of data in bytes - * + * @alloc_kernel_memory: flag to indicate memory allocation */ -int security_read_policy(struct selinux_state *state, - void **data, size_t *len) +int security_read_selinux_policy(struct selinux_state *state, + void **data, size_t *len, + bool alloc_kernel_memory)
Instead of passing in a boolean to control how the memory is allocated, split this into a helper function that takes an already-allocated buffer and two different front-end wrappers, one for kernel-internal use and one for userspace use.
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@@ -3738,7 +3739,10 @@ int security_read_policy(struct selinux_state *state, *len = security_policydb_len(state); - *data = vmalloc_user(*len); + if (alloc_kernel_memory) + *data = kzalloc(*len, GFP_KERNEL);
You need vmalloc() since policy image size may exceed kmalloc max (or at least that used to be the case).