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lkdtm: Add READ_AFTER_FREE test 

In a similar manner to WRITE_AFTER_FREE, add a READ_AFTER_FREE
test to test free poisoning features. Sample output when
no sanitization is present:

 # echo READ_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[   17.542473] lkdtm: Performing direct entry READ_AFTER_FREE
[   17.543866] lkdtm: Value in memory before free: 12345678
[   17.545212] lkdtm: Attempting bad read from freed memory
[   17.546542] lkdtm: Memory was not poisoned

with slub_debug=P:

 # echo READ_AFTER_FREE > /sys/kernel/debug/provoke-crash/DIRECT
[   22.415531] lkdtm: Performing direct entry READ_AFTER_FREE
[   22.416366] lkdtm: Value in memory before free: 12345678
[   22.417137] lkdtm: Attempting bad read from freed memory
[   22.417897] lkdtm: Memory correctly poisoned, calling BUG

Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Laura Abbott 2016-02-25 16:36:42 -08:00 committed by Kees Cook
parent ea861d73a9
commit bc0b8cc6cb
1 changed files with 38 additions and 0 deletions
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38
drivers/misc/lkdtm.c
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@ -92,6 +92,7 @@ enum ctype {
CT_UNALIGNED_LOAD_STORE_WRITE,
CT_OVERWRITE_ALLOCATION,
CT_WRITE_AFTER_FREE,
CT_READ_AFTER_FREE,
CT_SOFTLOCKUP,
CT_HARDLOCKUP,
CT_SPINLOCKUP,
@ -129,6 +130,7 @@ static char* cp_type[] = {
"UNALIGNED_LOAD_STORE_WRITE",
"OVERWRITE_ALLOCATION",
"WRITE_AFTER_FREE",
"READ_AFTER_FREE",
"SOFTLOCKUP",
"HARDLOCKUP",
"SPINLOCKUP",
@ -417,6 +419,42 @@ static void lkdtm_do_action(enum ctype which)
memset(data, 0x78, len);
break;
}
case CT_READ_AFTER_FREE: {
int *base, *val, saw;
size_t len = 1024;
/*
* The slub allocator uses the first word to store the free
* pointer in some configurations. Use the middle of the
* allocation to avoid running into the freelist
*/
size_t offset = (len / sizeof(*base)) / 2;
base = kmalloc(len, GFP_KERNEL);
if (!base)
break;
val = kmalloc(len, GFP_KERNEL);
if (!val)
break;
*val = 0x12345678;
base[offset] = *val;
pr_info("Value in memory before free: %x\n", base[offset]);
kfree(base);
pr_info("Attempting bad read from freed memory\n");
saw = base[offset];
if (saw != *val) {
/* Good! Poisoning happened, so declare a win. */
pr_info("Memory correctly poisoned, calling BUG\n");
BUG();
}
pr_info("Memory was not poisoned\n");
kfree(val);
break;
}
case CT_SOFTLOCKUP:
preempt_disable();
for (;;)