Messages in this thread | | | Subject | Re: [PATCH 1/2] ima: Pre-parse the list of keyrings in a KEY_CHECK rule | From | Nayna <> | Date | Thu, 6 Aug 2020 11:34:43 -0400 |
| |
On 7/27/20 10:08 AM, Tyler Hicks wrote: > The ima_keyrings buffer was used as a work buffer for strsep()-based > parsing of the "keyrings=" option of an IMA policy rule. This parsing > was re-performed each time an asymmetric key was added to a kernel > keyring for each loaded policy rule that contained a "keyrings=" option. > > An example rule specifying this option is: > > measure func=KEY_CHECK keyrings=a|b|c > > The rule says to measure asymmetric keys added to any of the kernel > keyrings named "a", "b", or "c". The size of the buffer size was > equal to the size of the largest "keyrings=" value seen in a previously > loaded rule (5 + 1 for the NUL-terminator in the previous example) and > the buffer was pre-allocated at the time of policy load. > > The pre-allocated buffer approach suffered from a couple bugs: > > 1) There was no locking around the use of the buffer so concurrent key > add operations, to two different keyrings, would result in the > strsep() loop of ima_match_keyring() to modify the buffer at the same > time. This resulted in unexpected results from ima_match_keyring() > and, therefore, could cause unintended keys to be measured or keys to > not be measured when IMA policy intended for them to be measured. > > 2) If the kstrdup() that initialized entry->keyrings in ima_parse_rule() > failed, the ima_keyrings buffer was freed and set to NULL even when a > valid KEY_CHECK rule was previously loaded. The next KEY_CHECK event > would trigger a call to strcpy() with a NULL destination pointer and > crash the kernel. > > Remove the need for a pre-allocated global buffer by parsing the list of > keyrings in a KEY_CHECK rule at the time of policy load. The > ima_rule_entry will contain an array of string pointers which point to > the name of each keyring specified in the rule. No string processing > needs to happen at the time of asymmetric key add so iterating through > the list and doing a string comparison is all that's required at the > time of policy check. > > In the process of changing how the "keyrings=" policy option is handled, > a couple additional bugs were fixed: > > 1) The rule parser accepted rules containing invalid "keyrings=" values > such as "a|b||c", "a|b|", or simply "|". > > 2) The /sys/kernel/security/ima/policy file did not display the entire > "keyrings=" value if the list of keyrings was longer than what could > fit in the fixed size tbuf buffer in ima_policy_show(). > > Fixes: 5c7bac9fb2c5 ("IMA: pre-allocate buffer to hold keyrings string") > Fixes: 2b60c0ecedf8 ("IMA: Read keyrings= option from the IMA policy") > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com> > --- > security/integrity/ima/ima_policy.c | 138 +++++++++++++++++++--------- > 1 file changed, 93 insertions(+), 45 deletions(-) > > diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c > index 07f033634b27..c328cfa0fc49 100644 > --- a/security/integrity/ima/ima_policy.c > +++ b/security/integrity/ima/ima_policy.c > @@ -59,6 +59,11 @@ enum policy_types { ORIGINAL_TCB = 1, DEFAULT_TCB }; > > enum policy_rule_list { IMA_DEFAULT_POLICY = 1, IMA_CUSTOM_POLICY }; > > +struct ima_rule_opt_list { > + size_t count; > + char *items[]; > +}; > + > struct ima_rule_entry { > struct list_head list; > int action; > @@ -78,7 +83,7 @@ struct ima_rule_entry { > int type; /* audit type */ > } lsm[MAX_LSM_RULES]; > char *fsname; > - char *keyrings; /* Measure keys added to these keyrings */ > + struct ima_rule_opt_list *keyrings; /* Measure keys added to these keyrings */ > struct ima_template_desc *template; > }; > > @@ -206,10 +211,6 @@ static LIST_HEAD(ima_policy_rules); > static LIST_HEAD(ima_temp_rules); > static struct list_head *ima_rules = &ima_default_rules; > > -/* Pre-allocated buffer used for matching keyrings. */ > -static char *ima_keyrings; > -static size_t ima_keyrings_len; > - > static int ima_policy __initdata; > > static int __init default_measure_policy_setup(char *str) > @@ -253,6 +254,72 @@ static int __init default_appraise_policy_setup(char *str) > } > __setup("ima_appraise_tcb", default_appraise_policy_setup); > > +static struct ima_rule_opt_list *ima_alloc_rule_opt_list(const substring_t *src) > +{ > + struct ima_rule_opt_list *opt_list; > + size_t count = 0; > + char *src_copy; > + char *cur, *next; > + size_t i; > + > + src_copy = match_strdup(src); > + if (!src_copy) > + return NULL;
The caller of this function checks for IS_ERR(..) and not IS_ERR_OR_NULL(..). Shouldn't it return ERR_PTR(-EINVAL) instead of NULL ?
Thanks & Regards,
- Nayna
| |