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security: Allow more LSM callbacks than available slots #5

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security: Allow more LSM callbacks than available slots #5

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45 changes: 33 additions & 12 deletions security/security.c
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Original file line number Diff line number Diff line change
Expand Up @@ -436,28 +436,25 @@ static void __init lsm_init_hook_static_slot(struct static_slot *slots,
int *first_slot_idx)
{
struct security_hook_list *pos;
struct static_slot *slot;
int slot_cnt;
int slot_cnt, slot_idx;

slot_cnt = 0;
hlist_for_each_entry_rcu(pos, head, list)
slot_cnt++;

if (slot_cnt > SECURITY_STATIC_SLOT_COUNT)
panic("%s - No static hook slot remaining to add LSM hook.\n",
__func__);

if (slot_cnt == 0) {
*first_slot_idx = INT_MAX;
return;
}

*first_slot_idx = SECURITY_STATIC_SLOT_COUNT - slot_cnt;
slot = slots + *first_slot_idx;
slot_idx = *first_slot_idx;
hlist_for_each_entry_rcu(pos, head, list) {
__static_call_update(slot->key, slot->trampoline,
pos->hook.generic_func);
slot++;
if (slot_idx >= 0)
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@bjackman bjackman Aug 25, 2020

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Shouldn't this be if slot_idx < SECURITY_STATIC_SLOT_COUNT?

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@PaulRenauld PaulRenauld Aug 26, 2020

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I didn't provide enough context here: the slots will hold the callbacks that are at the end of the linked list. This way, we can iterate over the first few elements of the list which are not in the slots.
E.g. if we have 10 slots and 15 callbacks, slot_idx will be -5 at first. It will skip the first 5 elements in the list, and then start adding the callbacks to the slots.

__static_call_update(slots[slot_idx].key,
slots[slot_idx].trampoline,
pos->hook.generic_func);
slot_idx++;
}
}

Expand Down Expand Up @@ -869,9 +866,20 @@ static void __init lsm_early_task(struct task_struct *task)

#define call_void_hook(FUNC, ...) do { \
switch (base_slot_idx.FUNC) { \
default : { /* Callbacks that don't fit in the static slots */ \
struct security_hook_list *__hook_list_pos; \
int __remaining = base_slot_idx.FUNC; \
hlist_for_each_entry(__hook_list_pos, \
&security_hook_heads.FUNC, list) { \
__hook_list_pos->hook.FUNC(__VA_ARGS__); \
if (++__remaining >= 0) \
break; \
} \
fallthrough; \
} \
SECURITY_FOREACH_STATIC_SLOT(__CASE_CALL_STATIC_VOID, \
FUNC, __VA_ARGS__) \
default : \
case INT_MAX: /* No callback registered */ \
break; \
} \
} while (0)
Expand All @@ -886,9 +894,22 @@ static void __init lsm_early_task(struct task_struct *task)
#define call_int_hook(FUNC, IRC, ...) ({ \
int RC = IRC; \
switch (base_slot_idx.FUNC) { \
default : { /* Callbacks that don't fit in the static slots */ \
struct security_hook_list *__hook_list_pos; \
int __remaining = base_slot_idx.FUNC; \
hlist_for_each_entry(__hook_list_pos, \
&security_hook_heads.FUNC, list) { \
RC = __hook_list_pos->hook.FUNC(__VA_ARGS__); \
if (RC != 0 || ++__remaining >= 0) \
break; \
} \
if (RC != 0) \
break; \
fallthrough; \
} \
SECURITY_FOREACH_STATIC_SLOT(__CASE_CALL_STATIC_INT, \
RC, FUNC, __VA_ARGS__) \
default : \
case INT_MAX: /* No callback registered */ \
break; \
} \
RC; \
Expand Down