From 685f577aa01ed378374cde9c0105b19c18ca7c07 Mon Sep 17 00:00:00 2001 From: James Carter Date: Wed, 9 Sep 2020 16:57:12 -0400 Subject: [PATCH] libsepol/cil: Validate constraint expressions before adding to binary policy 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 Signed-off-by: James Carter Acked-by: Stephen Smalley --- libsepol/cil/src/cil_binary.c | 48 ++++++++++++++++++++++++++++++++ libsepol/cil/src/cil_build_ast.c | 20 ++++--------- 2 files changed, 53 insertions(+), 15 deletions(-) diff --git a/libsepol/cil/src/cil_binary.c b/libsepol/cil/src/cil_binary.c index 7726685809af..c8e41f09e53f 100644 --- a/libsepol/cil/src/cil_binary.c +++ b/libsepol/cil/src/cil_binary.c @@ -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; diff --git a/libsepol/cil/src/cil_build_ast.c b/libsepol/cil/src/cil_build_ast.c index 60ecaaff3060..870c6923b4de 100644 --- a/libsepol/cil/src/cil_build_ast.c +++ b/libsepol/cil/src/cil_build_ast.c @@ -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; } -- 2.29.0.rc2