From 521e6a2f478a4c7a7c198c017d4d12e8667d89e7 Mon Sep 17 00:00:00 2001 From: Nicolas Iooss Date: Sat, 3 Oct 2020 15:19:08 +0200 Subject: [PATCH] libsepol/cil: fix signed overflow caused by using (1 << 31) - 1 When compiling SELinux userspace tools with -ftrapv (this option generates traps for signed overflow on addition, subtraction, multiplication operations, instead of silently wrapping around), semodule crashes when running the tests from scripts/ci/fedora-test-runner.sh in a Fedora 32 virtual machine: [root@localhost selinux-testsuite]# make test make -C policy load make[1]: Entering directory '/root/selinux-testsuite/policy' # Test for "expand-check = 0" in /etc/selinux/semanage.conf # General policy build make[2]: Entering directory '/root/selinux-testsuite/policy/test_policy' Compiling targeted test_policy module Creating targeted test_policy.pp policy package rm tmp/test_policy.mod.fc make[2]: Leaving directory '/root/selinux-testsuite/policy/test_policy' # General policy load domain_fd_use --> off /usr/sbin/semodule -i test_policy/test_policy.pp test_mlsconstrain.cil test_overlay_defaultrange.cil test_add_levels.cil test_glblub.cil make[1]: *** [Makefile:174: load] Aborted (core dumped) Using "coredumpctl gdb" leads to the following strack trace: (gdb) bt #0 0x00007f608fe4fa25 in raise () from /lib64/libc.so.6 #1 0x00007f608fe38895 in abort () from /lib64/libc.so.6 #2 0x00007f6090028aca in __addvsi3.cold () from /lib64/libsepol.so.1 #3 0x00007f6090096f59 in __avrule_xperm_setrangebits (low=30, high=30, xperms=0x8b9eea0) at ../cil/src/cil_binary.c:1551 #4 0x00007f60900970dd in __cil_permx_bitmap_to_sepol_xperms_list (xperms=0xb650a30, xperms_list=0x7ffce2653b18) at ../cil/src/cil_binary.c:1596 #5 0x00007f6090097286 in __cil_avrulex_ioctl_to_policydb (k=0xb8ec200 "@\023\214\022\006", datum=0xb650a30, args=0x239a640) at ../cil/src/cil_binary.c:1649 #6 0x00007f609003f1e5 in hashtab_map (h=0x41f8710, apply=0x7f60900971da <__cil_avrulex_ioctl_to_policydb>, args=0x239a640) at hashtab.c:234 #7 0x00007f609009ea19 in cil_binary_create_allocated_pdb (db=0x2394f10, policydb=0x239a640) at ../cil/src/cil_binary.c:4969 #8 0x00007f609009d19d in cil_binary_create (db=0x2394f10, policydb=0x7ffce2653d30) at ../cil/src/cil_binary.c:4329 #9 0x00007f609008ec23 in cil_build_policydb_create_pdb (db=0x2394f10, sepol_db=0x7ffce2653d30) at ../cil/src/cil.c:631 #10 0x00007f608fff4bf3 in semanage_direct_commit () from /lib64/libsemanage.so.1 #11 0x00007f608fff9fae in semanage_commit () from /lib64/libsemanage.so.1 #12 0x0000000000403e2b in main (argc=7, argv=0x7ffce2655058) at semodule.c:753 (gdb) f 3 #3 0x00007f6090096f59 in __avrule_xperm_setrangebits (low=30, high=30, xperms=0x8b9eea0) at ../cil/src/cil_binary.c:1551 1551 xperms->perms[i] |= XPERM_SETBITS(h) - XPERM_SETBITS(low); A signed integer overflow therefore occurs in XPERM_SETBITS(h): #define XPERM_SETBITS(x) ((1 << (x & 0x1f)) - 1) This macro is expanded with h=31, so "(1 << 31) - 1" is computed: * (1 << 31) = -0x80000000 is the lowest signed 32-bit integer value * (1 << 31) - 1 overflows the capacity of a signed 32-bit integer and results in 0x7fffffff (which is unsigned) Using unsigned integers (with "1U") fixes the crash, as (1U << 31) = 0x80000000U has no overflowing issues. Signed-off-by: Nicolas Iooss Acked-by: Petr Lautrbach --- libsepol/cil/src/cil_binary.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libsepol/cil/src/cil_binary.c b/libsepol/cil/src/cil_binary.c index 36720eda4549..e417c5c28b8b 100644 --- a/libsepol/cil/src/cil_binary.c +++ b/libsepol/cil/src/cil_binary.c @@ -1526,7 +1526,7 @@ int cil_avrule_to_policydb(policydb_t *pdb, const struct cil_db *db, struct cil_ /* index of the u32 containing the permission */ #define XPERM_IDX(x) (x >> 5) /* set bits 0 through x-1 within the u32 */ -#define XPERM_SETBITS(x) ((1 << (x & 0x1f)) - 1) +#define XPERM_SETBITS(x) ((1U << (x & 0x1f)) - 1) /* low value for this u32 */ #define XPERM_LOW(x) (x << 5) /* high value for this u32 */ -- 2.29.0.rc2