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libsepol/cil: Validate constraint expressions before adding to binary policy

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CIL was not correctly determining the depth of constraint expressions
which prevented it from giving an error when the max depth was exceeded.
This allowed invalid policy binaries with constraint expressions exceeding
the max depth to be created.

Validate the constraint expression using the same logic that is used
when reading the binary policy. This includes checking the depth of the
the expression.

Reported-by: Jonathan Hettwer <j2468h@gmail.com>
Signed-off-by: James Carter <jwcart2@gmail.com>
Acked-by: Stephen Smalley <stephen.smalley.work@gmail.com>
This commit is contained in:
James Carter 2020-09-09 16:57:12 -04:00 committed by Stephen Smalley
parent 8bc865e1fe
commit 685f577aa0
2 changed files with 53 additions and 15 deletions
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48
libsepol/cil/src/cil_binary.c
View File

@ -2713,6 +2713,49 @@ int __cil_constrain_expr_to_sepol_expr(policydb_t *pdb, const struct cil_db *db,
return SEPOL_OK;
}
int __cil_validate_constrain_expr(constraint_expr_t *sepol_expr)
{
constraint_expr_t *e;
int depth = -1;
for (e = sepol_expr; e != NULL; e = e->next) {
switch (e->expr_type) {
case CEXPR_NOT:
if (depth < 0) {
cil_log(CIL_ERR,"Invalid constraint expression\n");
return SEPOL_ERR;
}
break;
case CEXPR_AND:
case CEXPR_OR:
if (depth < 1) {
cil_log(CIL_ERR,"Invalid constraint expression\n");
return SEPOL_ERR;
}
depth--;
break;
case CEXPR_ATTR:
case CEXPR_NAMES:
if (depth == (CEXPR_MAXDEPTH - 1)) {
cil_log(CIL_ERR,"Constraint expression exceeded max allowable depth\n");
return SEPOL_ERR;
}
depth++;
break;
default:
cil_log(CIL_ERR,"Invalid constraint expression\n");
return SEPOL_ERR;
}
}
if (depth != 0) {
cil_log(CIL_ERR,"Invalid constraint expression\n");
return SEPOL_ERR;
}
return SEPOL_OK;
}
int cil_constrain_to_policydb_helper(policydb_t *pdb, const struct cil_db *db, struct cil_symtab_datum *class, struct cil_list *perms, struct cil_list *expr)
{
int rc = SEPOL_ERR;
@ -2736,6 +2779,11 @@ int cil_constrain_to_policydb_helper(policydb_t *pdb, const struct cil_db *db, s
goto exit;
}
rc = __cil_validate_constrain_expr(sepol_expr);
if (rc != SEPOL_OK) {
goto exit;
}
sepol_constrain->expr = sepol_expr;
sepol_constrain->next = sepol_class->constraints;
sepol_class->constraints = sepol_constrain;

20
libsepol/cil/src/cil_build_ast.c
View File

@ -2738,7 +2738,7 @@ exit:
return SEPOL_ERR;
}
static int __cil_fill_constraint_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list **expr, int *depth)
static int __cil_fill_constraint_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list **expr)
{
int rc = SEPOL_ERR;
enum cil_flavor op;
@ -2750,12 +2750,6 @@ static int __cil_fill_constraint_expr(struct cil_tree_node *current, enum cil_fl
goto exit;
}
if (*depth > CEXPR_MAXDEPTH) {
cil_log(CIL_ERR, "Max depth of %d exceeded for constraint expression\n", CEXPR_MAXDEPTH);
rc = SEPOL_ERR;
goto exit;
}
op = __cil_get_constraint_operator_flavor(current->data);
rc = cil_verify_constraint_expr_syntax(current, op);
@ -2769,14 +2763,13 @@ static int __cil_fill_constraint_expr(struct cil_tree_node *current, enum cil_fl
case CIL_CONS_DOM:
case CIL_CONS_DOMBY:
case CIL_CONS_INCOMP:
(*depth)++;
rc = __cil_fill_constraint_leaf_expr(current, flavor, op, expr);
if (rc != SEPOL_OK) {
goto exit;
}
break;
case CIL_NOT:
rc = __cil_fill_constraint_expr(current->next->cl_head, flavor, &lexpr, depth);
rc = __cil_fill_constraint_expr(current->next->cl_head, flavor, &lexpr);
if (rc != SEPOL_OK) {
goto exit;
}
@ -2785,11 +2778,11 @@ static int __cil_fill_constraint_expr(struct cil_tree_node *current, enum cil_fl
cil_list_append(*expr, CIL_LIST, lexpr);
break;
default:
rc = __cil_fill_constraint_expr(current->next->cl_head, flavor, &lexpr, depth);
rc = __cil_fill_constraint_expr(current->next->cl_head, flavor, &lexpr);
if (rc != SEPOL_OK) {
goto exit;
}
rc = __cil_fill_constraint_expr(current->next->next->cl_head, flavor, &rexpr, depth);
rc = __cil_fill_constraint_expr(current->next->next->cl_head, flavor, &rexpr);
if (rc != SEPOL_OK) {
cil_list_destroy(&lexpr, CIL_TRUE);
goto exit;
@ -2801,8 +2794,6 @@ static int __cil_fill_constraint_expr(struct cil_tree_node *current, enum cil_fl
break;
}
(*depth)--;
return SEPOL_OK;
exit:
@ -2812,13 +2803,12 @@ exit:
int cil_gen_constraint_expr(struct cil_tree_node *current, enum cil_flavor flavor, struct cil_list **expr)
{
int rc = SEPOL_ERR;
int depth = 0;
if (current->cl_head == NULL) {
goto exit;
}
rc = __cil_fill_constraint_expr(current->cl_head, flavor, expr, &depth);
rc = __cil_fill_constraint_expr(current->cl_head, flavor, expr);
if (rc != SEPOL_OK) {
goto exit;
}