[PATCH v2 1/1] libsepol/cil: do not heap-overflow when too many permissions are in a class

[Nicolas Iooss <nicolas.iooss@xxxxxxx>]

When compiling a CIL policy with more than 32 items in a class (e.g. in
(class capability (chown ...)) with many items),
cil_classorder_to_policydb() overflows perm_value_to_cil[class_index]
array. As this array is allocated on the heap through
calloc(PERMS_PER_CLASS+1, sizeof(...)), this makes secilc crash with the
following message:

    *** Error in `/usr/bin/secilc': double free or corruption (!prev): 0x000000000062be80 ***
    ======= Backtrace: =========
    /usr/lib/libc.so.6(+0x70c4b)[0x7ffff76a7c4b]
    /usr/lib/libc.so.6(+0x76fe6)[0x7ffff76adfe6]
    /usr/lib/libc.so.6(+0x777de)[0x7ffff76ae7de]
    /lib/libsepol.so.1(+0x14fbda)[0x7ffff7b24bda]
    /lib/libsepol.so.1(+0x152db8)[0x7ffff7b27db8]
    /lib/libsepol.so.1(cil_build_policydb+0x63)[0x7ffff7af8723]
    /usr/bin/secilc[0x40273b]
    /usr/lib/libc.so.6(__libc_start_main+0xf1)[0x7ffff7657291]
    /usr/bin/secilc[0x402f7a]

Fix this by detecting the overflow before adding new permissions to a
class.

This bug has been found by fuzzing secilc with american fuzzy lop.

Signed-off-by: Nicolas Iooss <nicolas.iooss@xxxxxxx>
---
v2: check that sepol_common->permissions.nprim would not make
  sepol_class->permissions.nprim overflow when added to it.

 libsepol/cil/src/cil_binary.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/libsepol/cil/src/cil_binary.c b/libsepol/cil/src/cil_binary.c
index cc73648ad1b7..f83dc2ddd1ee 100644
--- a/libsepol/cil/src/cil_binary.c
+++ b/libsepol/cil/src/cil_binary.c
@@ -332,6 +332,12 @@ int cil_classorder_to_policydb(policydb_t *pdb, const struct cil_db *db, struct
 					goto exit;
 				}
 			}
+			if (sepol_common->permissions.nprim > PERMS_PER_CLASS ||
+			    sepol_class->permissions.nprim + sepol_common->permissions.nprim > PERMS_PER_CLASS) {
+				cil_log(CIL_ERR, "Too many permissions in class '%s'\n", cil_class->datum.fqn);
+				rc = SEPOL_ERR;
+				goto exit;
+			}
 			sepol_class->comdatum = sepol_common;
 			sepol_class->comkey = cil_strdup(key);
 			sepol_class->permissions.nprim += sepol_common->permissions.nprim;
@@ -344,9 +350,15 @@ int cil_classorder_to_policydb(policydb_t *pdb, const struct cil_db *db, struct
 
 		for (curr = NODE(cil_class)->cl_head; curr; curr = curr->next) {
 			struct cil_perm *cil_perm = curr->data;
-			perm_datum_t *sepol_perm = cil_malloc(sizeof(*sepol_perm));
-			memset(sepol_perm, 0, sizeof(perm_datum_t));
+			perm_datum_t *sepol_perm;
 
+			if (sepol_class->permissions.nprim + 1 > PERMS_PER_CLASS) {
+				cil_log(CIL_ERR, "Too many permissions in class '%s'\n", cil_class->datum.fqn);
+				rc = SEPOL_ERR;
+				goto exit;
+			}
+			sepol_perm = cil_malloc(sizeof(*sepol_perm));
+			memset(sepol_perm, 0, sizeof(perm_datum_t));
 			key = cil_strdup(cil_perm->datum.fqn);
 			rc = hashtab_insert(sepol_class->permissions.table, key, sepol_perm);
 			if (rc != SEPOL_OK) {
-- 
2.10.0

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