On 29/09/16 00:44, William Roberts wrote: > On Wed, Sep 28, 2016 at 5:34 PM, Nicolas Iooss <nicolas.iooss@xxxxxxx> wrote: >> On 28/09/16 23:06, William Roberts wrote: >>> On Sep 28, 2016 17:02, "Nicolas Iooss" <nicolas.iooss@xxxxxxx >>> <mailto:nicolas.iooss@xxxxxxx>> wrote: >>>> >>>> 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 >>> <mailto:nicolas.iooss@xxxxxxx>> >>>> --- >>>> libsepol/cil/src/cil_binary.c | 15 +++++++++++++-- >>>> 1 file changed, 13 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/libsepol/cil/src/cil_binary.c b/libsepol/cil/src/cil_binary.c >>>> index cc73648ad1b7..d3b3e90df45b 100644 >>>> --- a/libsepol/cil/src/cil_binary.c >>>> +++ b/libsepol/cil/src/cil_binary.c >>>> @@ -332,6 +332,11 @@ int cil_classorder_to_policydb(policydb_t *pdb, >>> const struct cil_db *db, struct >>>> goto exit; >>>> } >>>> } >>>> + if (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 +349,15 @@ 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) >>> >>> Is nprim input data? This could overflow here and be 0 right? You >>> probably want to check if nprim is saturated assuming unsigned. >> >> I mostly read the code of cil_classorder_to_policydb() in the way it is >> used in secilc: ...permissions.nprim is both the length of an array of >> perm_value_to_cil[] (off one) and the length of a linked list of CIL >> nodes. Therefore I did not consider the possibility of the addition to >> overflow here, and afterwards I still fail to see how it could overflow. >> >> In case you want to reproduce the bug, please find attached the source >> file I used (it is secilc/test/minimum.cil with 33 permissions defined >> in the first class). >> > > Its that both additions in that file, and the nprim++ statements are > ripe for overflows. > > All those additions occur based on the inputs from source code. > So, if you defined (uint32_t)~0 amount of classes, you should > be able to hit an overflow. nprim itself is a uint32_t. After a good night sleep I see now "rc = symtab_init(&sepol_class->permissions, PERM_SYMTAB_SIZE);" in cil_classorder_to_policydb(). This statement initializes sepol_class->permissions.nprim with 0. Later nprim is incremented both with sepol_common->permissions.nprim (which should be <= 32 and I will add a check for this) and one. If I define (uint32_t)~0 permissions in a CIL class object, I hit the if() when it crosses 32. Is there a way to make nprim equals to a value which would overflow that I am missing? -- Nicolas _______________________________________________ Selinux mailing list Selinux@xxxxxxxxxxxxx To unsubscribe, send email to Selinux-leave@xxxxxxxxxxxxx. To get help, send an email containing "help" to Selinux-request@xxxxxxxxxxxxx.
