KASAN: use-after-free Read in tomoyo_realpath_from_path

KASAN: use-after-free Read in tomoyo_realpath_from_path

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    788a0249 Merge tag 'arc-5.2-rc4' of git://git.kernel.org/p..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=179848d4a00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=60564cb52ab29d5b
dashboard link: https://syzkaller.appspot.com/bug?extid=0341f6a4d729d4e0acf1
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13ac35baa00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in tomoyo_get_socket_name  
security/tomoyo/realpath.c:238 [inline]
BUG: KASAN: use-after-free in tomoyo_realpath_from_path+0x722/0x7a0  
security/tomoyo/realpath.c:284
Read of size 2 at addr ffff8880a91276d0 by task syz-executor.3/17397

CPU: 0 PID: 17397 Comm: syz-executor.3 Not tainted 5.2.0-rc3+ #12
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
  print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
  __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
  kasan_report+0x12/0x20 mm/kasan/common.c:614
  __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:130
  tomoyo_get_socket_name security/tomoyo/realpath.c:238 [inline]
  tomoyo_realpath_from_path+0x722/0x7a0 security/tomoyo/realpath.c:284
  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
  tomoyo_check_open_permission+0x2a8/0x3f0 security/tomoyo/file.c:771
  tomoyo_file_open security/tomoyo/tomoyo.c:319 [inline]
  tomoyo_file_open+0xa9/0xd0 security/tomoyo/tomoyo.c:314
  security_file_open+0x71/0x300 security/security.c:1454
  do_dentry_open+0x373/0x1250 fs/open.c:765
  vfs_open+0xa0/0xd0 fs/open.c:887
  do_last fs/namei.c:3416 [inline]
  path_openat+0x10e9/0x46d0 fs/namei.c:3533
  do_filp_open+0x1a1/0x280 fs/namei.c:3563
  do_sys_open+0x3fe/0x5d0 fs/open.c:1070
  __do_sys_open fs/open.c:1088 [inline]
  __se_sys_open fs/open.c:1083 [inline]
  __x64_sys_open+0x7e/0xc0 fs/open.c:1083
  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x413161
Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48  
83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007f65230f8bb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000413161
RDX: fffffffffffffffa RSI: 0000000000000000 RDI: 00007f65230f8bd0
RBP: 000000000075c060 R08: 0000000000000050 R09: 000000000000000f
R10: 0000000000000004 R11: 0000000000000293 R12: 00007f65230f96d4
R13: 00000000004c83f6 R14: 00000000004dea40 R15: 00000000ffffffff

Allocated by task 17373:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_kmalloc mm/kasan/common.c:489 [inline]
  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
  __do_kmalloc mm/slab.c:3660 [inline]
  __kmalloc+0x15c/0x740 mm/slab.c:3669
  kmalloc include/linux/slab.h:552 [inline]
  sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1602
  sk_alloc+0x39/0xf70 net/core/sock.c:1656
  base_sock_create drivers/isdn/mISDN/socket.c:758 [inline]
  mISDN_sock_create+0xb4/0x3a0 drivers/isdn/mISDN/socket.c:780
  __sock_create+0x3d8/0x730 net/socket.c:1424
  sock_create net/socket.c:1475 [inline]
  __sys_socket+0x103/0x220 net/socket.c:1517
  __do_sys_socket net/socket.c:1526 [inline]
  __se_sys_socket net/socket.c:1524 [inline]
  __x64_sys_socket+0x73/0xb0 net/socket.c:1524
  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 17371:
  save_stack+0x23/0x90 mm/kasan/common.c:71
  set_track mm/kasan/common.c:79 [inline]
  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
  __cache_free mm/slab.c:3432 [inline]
  kfree+0xcf/0x220 mm/slab.c:3755
  sk_prot_free net/core/sock.c:1639 [inline]
  __sk_destruct+0x4f7/0x6e0 net/core/sock.c:1725
  sk_destruct+0x7b/0x90 net/core/sock.c:1733
  __sk_free+0xce/0x300 net/core/sock.c:1744
  sk_free+0x42/0x50 net/core/sock.c:1755
  sock_put include/net/sock.h:1723 [inline]
  base_sock_release+0x269/0x279 drivers/isdn/mISDN/socket.c:628
  __sock_release+0xce/0x2a0 net/socket.c:601
  sock_close+0x1b/0x30 net/socket.c:1273
  __fput+0x2ff/0x890 fs/file_table.c:280
  ____fput+0x16/0x20 fs/file_table.c:313
  task_work_run+0x145/0x1c0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:185 [inline]
  exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
  prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
  do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a91276c0
  which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 16 bytes inside of
  2048-byte region [ffff8880a91276c0, ffff8880a9127ec0)
The buggy address belongs to the page:
page:ffffea0002a44980 refcount:1 mapcount:0 mapping:ffff8880aa400c40  
index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea00022c9f88 ffffea0002234408 ffff8880aa400c40
raw: 0000000000000000 ffff8880a91265c0 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8880a9127580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a9127600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> ffff8880a9127680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                  ^
  ffff8880a9127700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8880a9127780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

Re: KASAN: use-after-free Read in tomoyo_realpath_from_path

[Tetsuo Handa]

Hello, Al.

syzbot found that SOCKET_I(d_backing_inode("struct path"->dentry))->sk
was already kfree()d when trying to calculate pathname for open().
"struct path"->dentry should remain valid but portion of memory
reachable via inode already became invalid. What should we do?

On 2019/06/06 3:42, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    788a0249 Merge tag 'arc-5.2-rc4' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=179848d4a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=60564cb52ab29d5b
> dashboard link: https://syzkaller.appspot.com/bug?extid=0341f6a4d729d4e0acf1
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13ac35baa00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com
> 
> ==================================================================
> BUG: KASAN: use-after-free in tomoyo_get_socket_name security/tomoyo/realpath.c:238 [inline]
> BUG: KASAN: use-after-free in tomoyo_realpath_from_path+0x722/0x7a0 security/tomoyo/realpath.c:284
> Read of size 2 at addr ffff8880a91276d0 by task syz-executor.3/17397
> 
> CPU: 0 PID: 17397 Comm: syz-executor.3 Not tainted 5.2.0-rc3+ #12
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
>  print_address_description.cold+0x7c/0x20d mm/kasan/report.c:188
>  __kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
>  kasan_report+0x12/0x20 mm/kasan/common.c:614
>  __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:130
>  tomoyo_get_socket_name security/tomoyo/realpath.c:238 [inline]
>  tomoyo_realpath_from_path+0x722/0x7a0 security/tomoyo/realpath.c:284
>  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
>  tomoyo_check_open_permission+0x2a8/0x3f0 security/tomoyo/file.c:771
>  tomoyo_file_open security/tomoyo/tomoyo.c:319 [inline]
>  tomoyo_file_open+0xa9/0xd0 security/tomoyo/tomoyo.c:314
>  security_file_open+0x71/0x300 security/security.c:1454
>  do_dentry_open+0x373/0x1250 fs/open.c:765
>  vfs_open+0xa0/0xd0 fs/open.c:887
>  do_last fs/namei.c:3416 [inline]
>  path_openat+0x10e9/0x46d0 fs/namei.c:3533
>  do_filp_open+0x1a1/0x280 fs/namei.c:3563
>  do_sys_open+0x3fe/0x5d0 fs/open.c:1070
>  __do_sys_open fs/open.c:1088 [inline]
>  __se_sys_open fs/open.c:1083 [inline]
>  __x64_sys_open+0x7e/0xc0 fs/open.c:1083
>  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x413161
> Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d 01
> RSP: 002b:00007f65230f8bb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
> RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000413161
> RDX: fffffffffffffffa RSI: 0000000000000000 RDI: 00007f65230f8bd0
> RBP: 000000000075c060 R08: 0000000000000050 R09: 000000000000000f
> R10: 0000000000000004 R11: 0000000000000293 R12: 00007f65230f96d4
> R13: 00000000004c83f6 R14: 00000000004dea40 R15: 00000000ffffffff
> 
> Allocated by task 17373:
>  save_stack+0x23/0x90 mm/kasan/common.c:71
>  set_track mm/kasan/common.c:79 [inline]
>  __kasan_kmalloc mm/kasan/common.c:489 [inline]
>  __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:462
>  kasan_kmalloc+0x9/0x10 mm/kasan/common.c:503
>  __do_kmalloc mm/slab.c:3660 [inline]
>  __kmalloc+0x15c/0x740 mm/slab.c:3669
>  kmalloc include/linux/slab.h:552 [inline]
>  sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1602
>  sk_alloc+0x39/0xf70 net/core/sock.c:1656
>  base_sock_create drivers/isdn/mISDN/socket.c:758 [inline]
>  mISDN_sock_create+0xb4/0x3a0 drivers/isdn/mISDN/socket.c:780
>  __sock_create+0x3d8/0x730 net/socket.c:1424
>  sock_create net/socket.c:1475 [inline]
>  __sys_socket+0x103/0x220 net/socket.c:1517
>  __do_sys_socket net/socket.c:1526 [inline]
>  __se_sys_socket net/socket.c:1524 [inline]
>  __x64_sys_socket+0x73/0xb0 net/socket.c:1524
>  do_syscall_64+0xfd/0x680 arch/x86/entry/common.c:301
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 17371:
>  save_stack+0x23/0x90 mm/kasan/common.c:71
>  set_track mm/kasan/common.c:79 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/common.c:451
>  kasan_slab_free+0xe/0x10 mm/kasan/common.c:459
>  __cache_free mm/slab.c:3432 [inline]
>  kfree+0xcf/0x220 mm/slab.c:3755
>  sk_prot_free net/core/sock.c:1639 [inline]
>  __sk_destruct+0x4f7/0x6e0 net/core/sock.c:1725
>  sk_destruct+0x7b/0x90 net/core/sock.c:1733
>  __sk_free+0xce/0x300 net/core/sock.c:1744
>  sk_free+0x42/0x50 net/core/sock.c:1755
>  sock_put include/net/sock.h:1723 [inline]
>  base_sock_release+0x269/0x279 drivers/isdn/mISDN/socket.c:628
>  __sock_release+0xce/0x2a0 net/socket.c:601
>  sock_close+0x1b/0x30 net/socket.c:1273
>  __fput+0x2ff/0x890 fs/file_table.c:280
>  ____fput+0x16/0x20 fs/file_table.c:313
>  task_work_run+0x145/0x1c0 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:185 [inline]
>  exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:168
>  prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
>  syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
>  do_syscall_64+0x58e/0x680 arch/x86/entry/common.c:304
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> The buggy address belongs to the object at ffff8880a91276c0
>  which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 16 bytes inside of
>  2048-byte region [ffff8880a91276c0, ffff8880a9127ec0)
> The buggy address belongs to the page:
> page:ffffea0002a44980 refcount:1 mapcount:0 mapping:ffff8880aa400c40 index:0x0 compound_mapcount: 0
> flags: 0x1fffc0000010200(slab|head)
> raw: 01fffc0000010200 ffffea00022c9f88 ffffea0002234408 ffff8880aa400c40
> raw: 0000000000000000 ffff8880a91265c0 0000000100000003 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8880a9127580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880a9127600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>> ffff8880a9127680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>                                                  ^
>  ffff8880a9127700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8880a9127780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

Re: KASAN: use-after-free Read in tomoyo_realpath_from_path

[Tetsuo Handa]

Here is a reproducer.

The problem is that TOMOYO is accessing already freed socket from security_file_open()
which later fails with -ENXIO (because we can't get file descriptor of sockets via
/proc/pid/fd/n interface), and the file descriptor is getting released before
security_file_open() completes because we do not raise "struct file"->f_count of
the file which is accessible via /proc/pid/fd/n interface. We can avoid this problem
if we can avoid calling security_file_open() which after all fails with -ENXIO.
How should we handle this race? Let LSM modules check if security_file_open() was
called on a socket?

----------------------------------------
diff --git a/fs/open.c b/fs/open.c
index b5b80469b93d..995ffcb37128 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -765,6 +765,12 @@ static int do_dentry_open(struct file *f,
 	error = security_file_open(f);
 	if (error)
 		goto cleanup_all;
+	if (!strcmp(current->comm, "a.out") &&
+	    f->f_path.dentry->d_sb->s_magic == SOCKFS_MAGIC) {
+		printk("Start open(socket) delay\n");
+		schedule_timeout_killable(HZ * 5);
+		printk("End open(socket) delay\n");
+	}
 
 	error = break_lease(locks_inode(f), f->f_flags);
 	if (error)
----------------------------------------

----------------------------------------
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/socket.h>

int main(int argc, char *argv[])
{
	pid_t pid = getpid();
	int fd = socket(AF_ISDN, SOCK_RAW, 0);
	char buffer[128] = { };
	if (fork() == 0) {
		close(fd);
		snprintf(buffer, sizeof(buffer) - 1, "/proc/%u/fd/%u", pid, fd);
		open(buffer, 3);
		_exit(0);
	}
	sleep(2);
	close(fd);
	return 0;
}
----------------------------------------

----------------------------------------
getpid()                                = 32504
socket(AF_ISDN, SOCK_RAW, 0)            = 3
clone(strace: Process 32505 attached
child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7efea30dda10) = 32505
[pid 32504] rt_sigprocmask(SIG_BLOCK, [CHLD],  <unfinished ...>
[pid 32505] close(3 <unfinished ...>
[pid 32504] <... rt_sigprocmask resumed> [], 8) = 0
[pid 32505] <... close resumed> )       = 0
[pid 32504] rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
[pid 32505] open("/proc/32504/fd/3", O_ACCMODE <unfinished ...>
[pid 32504] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
[pid 32504] nanosleep({2, 0}, 0x7ffd3c608150) = 0
[pid 32504] close(3)                    = 0
[pid 32504] exit_group(0)               = ?
[pid 32504] +++ exited with 0 +++
<... open resumed> )                    = -1 ENXIO (No such device or address)
exit_group(0)                           = ?
----------------------------------------

----------------------------------------
[   95.109628] Start open(socket) delay
[   97.113150] base_sock_release(00000000506a3239) sk=00000000016d0ceb
[  100.142235] End open(socket) delay
----------------------------------------

Re: KASAN: use-after-free Read in tomoyo_realpath_from_path

[Tetsuo Handa]

Tetsuo Handa wrote:
> The problem is that TOMOYO is accessing already freed socket from security_file_open()
> which later fails with -ENXIO (because we can't get file descriptor of sockets via
> /proc/pid/fd/n interface), and the file descriptor is getting released before
> security_file_open() completes because we do not raise "struct file"->f_count of
> the file which is accessible via /proc/pid/fd/n interface. We can avoid this problem
> if we can avoid calling security_file_open() which after all fails with -ENXIO.
> How should we handle this race? Let LSM modules check if security_file_open() was
> called on a socket?

Well, just refusing security_file_open() is not sufficient, for open(O_PATH) allows installing
file descriptor where SOCKET_I(inode)->sk can change at any moment, and TOMOYO cannot tell
whether it is safe to access SOCKET_I(inode)->sk from security_inode_getattr().

But refusing open(O_PATH) as well might break userspace programs. Oh, no...

----------------------------------------
diff --git a/fs/open.c b/fs/open.c
index b5b80469b93d..ea69668e2cd8 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -728,6 +728,16 @@ static int do_dentry_open(struct file *f,
 	/* Ensure that we skip any errors that predate opening of the file */
 	f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
 
+	/*
+	 * Sockets must not be opened via /proc/pid/fd/n, even with O_PATH,
+	 * for SOCKET_I(inode)->sk can be kfree()d at any moment after a file
+	 * descriptor obtained by opening /proc/pid/fd/n was installed.
+	 */
+	if (unlikely(S_ISSOCK(inode->i_mode))) {
+		error = (f->f_flags & O_PATH) ? -ENOENT : -ENXIO;
+		goto cleanup_file;
+	}
+
 	if (unlikely(f->f_flags & O_PATH)) {
 		f->f_mode = FMODE_PATH | FMODE_OPENED;
 		f->f_op = &empty_fops;
----------------------------------------

----------------------------------------
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/socket.h>

int main(int argc, char *argv[])
{
        pid_t pid = getpid();
        int fd = socket(AF_INET, SOCK_STREAM, 0);
        char buffer[128] = { };
        if (fork() == 0) {
                struct stat buf = { };
                close(fd);
                snprintf(buffer, sizeof(buffer) - 1, "/proc/%u/fd/%u", pid, fd);
                fd = open(buffer, __O_PATH);
                sleep(5);
                fstat(fd, &buf);
                _exit(0);
        }
        sleep(2);
        close(fd);
        return 0;
}
----------------------------------------

[PATCH] tomoyo: Don't check open/getattr permission on sockets.

[Tetsuo Handa]

syzbot is reporting that use of SOCKET_I()->sk from open() can result in
use after free problem [1], for socket's inode is still reachable via
/proc/pid/fd/n despite destruction of SOCKET_I()->sk already completed.

But there is no point with calling security_file_open() on sockets
because open("/proc/pid/fd/n", !O_PATH) on sockets fails with -ENXIO.

There is some point with calling security_inode_getattr() on sockets
because stat("/proc/pid/fd/n") and fstat(open("/proc/pid/fd/n", O_PATH))
are valid. If we want to access "struct sock"->sk_{family,type,protocol}
fields, we will need to use security_socket_post_create() hook and
security_inode_free() hook in order to remember these fields because
security_sk_free() hook is called before the inode is destructed. But
since information which can be protected by checking
security_inode_getattr() on sockets is trivial, let's not be bothered by
"struct inode"->i_security management.

There is point with calling security_file_ioctl() on sockets. Since
ioctl(open("/proc/pid/fd/n", O_PATH)) is invalid, security_file_ioctl()
on sockets should remain safe.

[1] https://syzkaller.appspot.com/bug?id=73d590010454403d55164cca23bd0565b1eb3b74

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com>
---
 security/tomoyo/tomoyo.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 716c92e..9661b86 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -126,6 +126,9 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
  */
 static int tomoyo_inode_getattr(const struct path *path)
 {
+	/* It is not safe to call tomoyo_get_socket_name(). */
+	if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode))
+		return 0;
 	return tomoyo_path_perm(TOMOYO_TYPE_GETATTR, path, NULL);
 }
 
@@ -316,6 +319,10 @@ static int tomoyo_file_open(struct file *f)
 	/* Don't check read permission here if called from do_execve(). */
 	if (current->in_execve)
 		return 0;
+	/* Sockets can't be opened by open(). */
+	if (f->f_path.dentry->d_inode &&
+	    S_ISSOCK(f->f_path.dentry->d_inode->i_mode))
+		return 0;
 	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
 					    f->f_flags);
 }
-- 
1.8.3.1

Re: [PATCH] tomoyo: Don't check open/getattr permission on sockets.

[Tetsuo Handa]

Hello, Al.

Q1: Do you agree that we should fix TOMOYO side rather than SOCKET_I()->sk
    management.

Q2: Do you see any problem with using f->f_path.dentry->d_inode ?
    Do we need to use d_backing_inode() or d_inode() ?

Regards.

On 2019/06/09 15:41, Tetsuo Handa wrote:
> syzbot is reporting that use of SOCKET_I()->sk from open() can result in
> use after free problem [1], for socket's inode is still reachable via
> /proc/pid/fd/n despite destruction of SOCKET_I()->sk already completed.
> 
> But there is no point with calling security_file_open() on sockets
> because open("/proc/pid/fd/n", !O_PATH) on sockets fails with -ENXIO.
> 
> There is some point with calling security_inode_getattr() on sockets
> because stat("/proc/pid/fd/n") and fstat(open("/proc/pid/fd/n", O_PATH))
> are valid. If we want to access "struct sock"->sk_{family,type,protocol}
> fields, we will need to use security_socket_post_create() hook and
> security_inode_free() hook in order to remember these fields because
> security_sk_free() hook is called before the inode is destructed. But
> since information which can be protected by checking
> security_inode_getattr() on sockets is trivial, let's not be bothered by
> "struct inode"->i_security management.
> 
> There is point with calling security_file_ioctl() on sockets. Since
> ioctl(open("/proc/pid/fd/n", O_PATH)) is invalid, security_file_ioctl()
> on sockets should remain safe.
> 
> [1] https://syzkaller.appspot.com/bug?id=73d590010454403d55164cca23bd0565b1eb3b74
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com>
> ---
>  security/tomoyo/tomoyo.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
> index 716c92e..9661b86 100644
> --- a/security/tomoyo/tomoyo.c
> +++ b/security/tomoyo/tomoyo.c
> @@ -126,6 +126,9 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
>   */
>  static int tomoyo_inode_getattr(const struct path *path)
>  {
> +	/* It is not safe to call tomoyo_get_socket_name(). */
> +	if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode))
> +		return 0;
>  	return tomoyo_path_perm(TOMOYO_TYPE_GETATTR, path, NULL);
>  }
>  
> @@ -316,6 +319,10 @@ static int tomoyo_file_open(struct file *f)
>  	/* Don't check read permission here if called from do_execve(). */
>  	if (current->in_execve)
>  		return 0;
> +	/* Sockets can't be opened by open(). */
> +	if (f->f_path.dentry->d_inode &&
> +	    S_ISSOCK(f->f_path.dentry->d_inode->i_mode))
> +		return 0;
>  	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
>  					    f->f_flags);
>  }
> 

Re: [PATCH] tomoyo: Don't check open/getattr permission on sockets.

[Al Viro]

On Sun, Jun 16, 2019 at 03:49:00PM +0900, Tetsuo Handa wrote:
> Hello, Al.
> 
> Q1: Do you agree that we should fix TOMOYO side rather than SOCKET_I()->sk
>     management.

You do realize that sockets are not unique in that respect, right?
All kinds of interesting stuff can be accessed via /proc/*/fd/*, and
it _can_ be closed under you.  So I'd suggest checking how your code
copes with similar for pipes, FIFOs, epoll, etc., accessed that way...

We are _not_ going to be checking that in fs/open.c - the stuff found
via /proc/*/fd/* can have the associated file closed by the time
we get to calling ->open() and we won't know that until said call.

> Q2: Do you see any problem with using f->f_path.dentry->d_inode ?
>     Do we need to use d_backing_inode() or d_inode() ?

Huh?  What's wrong with file_inode(f), in the first place?  And
just when can that be NULL, while we are at it?

> >  static int tomoyo_inode_getattr(const struct path *path)
> >  {
> > +	/* It is not safe to call tomoyo_get_socket_name(). */
> > +	if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode))
> > +		return 0;

Can that be called for a negative?

[PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[Tetsuo Handa]

On 2019/06/19 5:49, Al Viro wrote:
> On Sun, Jun 16, 2019 at 03:49:00PM +0900, Tetsuo Handa wrote:
>> Hello, Al.
>>
>> Q1: Do you agree that we should fix TOMOYO side rather than SOCKET_I()->sk
>>     management.
> 
> You do realize that sockets are not unique in that respect, right?
> All kinds of interesting stuff can be accessed via /proc/*/fd/*, and
> it _can_ be closed under you.  So I'd suggest checking how your code
> copes with similar for pipes, FIFOs, epoll, etc., accessed that way...

I know all kinds of interesting stuff can be accessed via /proc/*/fd/*,
and it _can_ be closed under me.

Regarding sockets, I was accessing "struct socket" memory and
"struct sock" memory which are outside of "struct inode" memory.

But regarding other objects, I am accessing "struct dentry" memory,
"struct super_block" memory and "struct inode" memory. I'm expecting
that these memory can't be kfree()d as long as "struct path" holds
a reference. Is my expectation correct?

> 
> We are _not_ going to be checking that in fs/open.c - the stuff found
> via /proc/*/fd/* can have the associated file closed by the time
> we get to calling ->open() and we won't know that until said call.

OK. Then, fixing TOMOYO side is the correct way.

> 
>> Q2: Do you see any problem with using f->f_path.dentry->d_inode ?
>>     Do we need to use d_backing_inode() or d_inode() ?
> 
> Huh?  What's wrong with file_inode(f), in the first place?  And
> just when can that be NULL, while we are at it?

Oh, I was not aware of file_inode(). Thanks.

> 
>>>  static int tomoyo_inode_getattr(const struct path *path)
>>>  {
>>> +	/* It is not safe to call tomoyo_get_socket_name(). */
>>> +	if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode))
>>> +		return 0;
> 
> Can that be called for a negative?
> 

I check for NULL when I'm not sure it is guaranteed to hold a valid pointer.
You meant "we are sure that path->dentry->d_inode is valid", don't you?

By the way, "negative" associates with IS_ERR() range. I guess that
"NULL" is the better name...

Anyway, here is V2 patch.

From c63c4074300921d6d1c33c3b8dc9c84ebfededf5 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sat, 22 Jun 2019 13:14:26 +0900
Subject: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

syzbot is reporting that use of SOCKET_I()->sk from open() can result in
use after free problem [1], for socket's inode is still reachable via
/proc/pid/fd/n despite destruction of SOCKET_I()->sk already completed.

But there is no point with calling security_file_open() on sockets
because open("/proc/pid/fd/n", !O_PATH) on sockets fails with -ENXIO.

There is some point with calling security_inode_getattr() on sockets
because stat("/proc/pid/fd/n") and fstat(open("/proc/pid/fd/n", O_PATH))
are valid. If we want to access "struct sock"->sk_{family,type,protocol}
fields, we will need to use security_socket_post_create() hook and
security_inode_free() hook in order to remember these fields because
security_sk_free() hook is called before the inode is destructed. But
since information which can be protected by checking
security_inode_getattr() on sockets is trivial, let's not be bothered by
"struct inode"->i_security management.

There is point with calling security_file_ioctl() on sockets. Since
ioctl(open("/proc/pid/fd/n", O_PATH)) is invalid, security_file_ioctl()
on sockets should remain safe.

[1] https://syzkaller.appspot.com/bug?id=73d590010454403d55164cca23bd0565b1eb3b74

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com>
---
 security/tomoyo/tomoyo.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 716c92e..8ea3f5d 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -126,6 +126,9 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
  */
 static int tomoyo_inode_getattr(const struct path *path)
 {
+	/* It is not safe to call tomoyo_get_socket_name(). */
+	if (S_ISSOCK(d_inode(path->dentry)->i_mode))
+		return 0;
 	return tomoyo_path_perm(TOMOYO_TYPE_GETATTR, path, NULL);
 }
 
@@ -316,6 +319,9 @@ static int tomoyo_file_open(struct file *f)
 	/* Don't check read permission here if called from do_execve(). */
 	if (current->in_execve)
 		return 0;
+	/* Sockets can't be opened by open(). */
+	if (S_ISSOCK(file_inode(f)->i_mode))
+		return 0;
 	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
 					    f->f_flags);
 }
-- 
1.8.3.1

Re: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[Eric Biggers]

Hi Tetsuo,

On Sat, Jun 22, 2019 at 01:45:30PM +0900, Tetsuo Handa wrote:
> On 2019/06/19 5:49, Al Viro wrote:
> > On Sun, Jun 16, 2019 at 03:49:00PM +0900, Tetsuo Handa wrote:
> >> Hello, Al.
> >>
> >> Q1: Do you agree that we should fix TOMOYO side rather than SOCKET_I()->sk
> >>     management.
> > 
> > You do realize that sockets are not unique in that respect, right?
> > All kinds of interesting stuff can be accessed via /proc/*/fd/*, and
> > it _can_ be closed under you.  So I'd suggest checking how your code
> > copes with similar for pipes, FIFOs, epoll, etc., accessed that way...
> 
> I know all kinds of interesting stuff can be accessed via /proc/*/fd/*,
> and it _can_ be closed under me.
> 
> Regarding sockets, I was accessing "struct socket" memory and
> "struct sock" memory which are outside of "struct inode" memory.
> 
> But regarding other objects, I am accessing "struct dentry" memory,
> "struct super_block" memory and "struct inode" memory. I'm expecting
> that these memory can't be kfree()d as long as "struct path" holds
> a reference. Is my expectation correct?
> 
> > 
> > We are _not_ going to be checking that in fs/open.c - the stuff found
> > via /proc/*/fd/* can have the associated file closed by the time
> > we get to calling ->open() and we won't know that until said call.
> 
> OK. Then, fixing TOMOYO side is the correct way.
> 
> > 
> >> Q2: Do you see any problem with using f->f_path.dentry->d_inode ?
> >>     Do we need to use d_backing_inode() or d_inode() ?
> > 
> > Huh?  What's wrong with file_inode(f), in the first place?  And
> > just when can that be NULL, while we are at it?
> 
> Oh, I was not aware of file_inode(). Thanks.
> 
> > 
> >>>  static int tomoyo_inode_getattr(const struct path *path)
> >>>  {
> >>> +	/* It is not safe to call tomoyo_get_socket_name(). */
> >>> +	if (path->dentry->d_inode && S_ISSOCK(path->dentry->d_inode->i_mode))
> >>> +		return 0;
> > 
> > Can that be called for a negative?
> > 
> 
> I check for NULL when I'm not sure it is guaranteed to hold a valid pointer.
> You meant "we are sure that path->dentry->d_inode is valid", don't you?
> 
> By the way, "negative" associates with IS_ERR() range. I guess that
> "NULL" is the better name...
> 
> Anyway, here is V2 patch.
> 
> From c63c4074300921d6d1c33c3b8dc9c84ebfededf5 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Sat, 22 Jun 2019 13:14:26 +0900
> Subject: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.
> 
> syzbot is reporting that use of SOCKET_I()->sk from open() can result in
> use after free problem [1], for socket's inode is still reachable via
> /proc/pid/fd/n despite destruction of SOCKET_I()->sk already completed.
> 
> But there is no point with calling security_file_open() on sockets
> because open("/proc/pid/fd/n", !O_PATH) on sockets fails with -ENXIO.
> 
> There is some point with calling security_inode_getattr() on sockets
> because stat("/proc/pid/fd/n") and fstat(open("/proc/pid/fd/n", O_PATH))
> are valid. If we want to access "struct sock"->sk_{family,type,protocol}
> fields, we will need to use security_socket_post_create() hook and
> security_inode_free() hook in order to remember these fields because
> security_sk_free() hook is called before the inode is destructed. But
> since information which can be protected by checking
> security_inode_getattr() on sockets is trivial, let's not be bothered by
> "struct inode"->i_security management.
> 
> There is point with calling security_file_ioctl() on sockets. Since
> ioctl(open("/proc/pid/fd/n", O_PATH)) is invalid, security_file_ioctl()
> on sockets should remain safe.
> 
> [1] https://syzkaller.appspot.com/bug?id=73d590010454403d55164cca23bd0565b1eb3b74
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com>
> ---
>  security/tomoyo/tomoyo.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
> index 716c92e..8ea3f5d 100644
> --- a/security/tomoyo/tomoyo.c
> +++ b/security/tomoyo/tomoyo.c
> @@ -126,6 +126,9 @@ static int tomoyo_bprm_check_security(struct linux_binprm *bprm)
>   */
>  static int tomoyo_inode_getattr(const struct path *path)
>  {
> +	/* It is not safe to call tomoyo_get_socket_name(). */
> +	if (S_ISSOCK(d_inode(path->dentry)->i_mode))
> +		return 0;
>  	return tomoyo_path_perm(TOMOYO_TYPE_GETATTR, path, NULL);
>  }
>  
> @@ -316,6 +319,9 @@ static int tomoyo_file_open(struct file *f)
>  	/* Don't check read permission here if called from do_execve(). */
>  	if (current->in_execve)
>  		return 0;
> +	/* Sockets can't be opened by open(). */
> +	if (S_ISSOCK(file_inode(f)->i_mode))
> +		return 0;
>  	return tomoyo_check_open_permission(tomoyo_domain(), &f->f_path,
>  					    f->f_flags);
>  }
> -- 

What happened to this patch?

Also, isn't the same bug in other places too?:

	- tomoyo_path_chmod()
	- tomoyo_path_chown()
	- smack_inode_getsecurity()
	- smack_inode_setsecurity()

- Eric

Re: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[Tetsuo Handa]

Eric Biggers wrote:
> What happened to this patch?

I have to learn how to manage a git tree for sending
pull requests, but I can't find time to try.

> 
> Also, isn't the same bug in other places too?:
> 
> 	- tomoyo_path_chmod()
> 	- tomoyo_path_chown()
> 	- smack_inode_getsecurity()
> 	- smack_inode_setsecurity()

What's the bug? The file descriptor returned by open(O_PATH) cannot be
passed to read(2), write(2), fchmod(2), fchown(2), fgetxattr(2), mmap(2) etc.

Re: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[Eric Biggers]

On Thu, Aug 22, 2019 at 03:55:31PM +0900, Tetsuo Handa wrote:
> Eric Biggers wrote:
> > What happened to this patch?
> 
> I have to learn how to manage a git tree for sending
> pull requests, but I can't find time to try.
> 
> > 
> > Also, isn't the same bug in other places too?:
> > 
> > 	- tomoyo_path_chmod()
> > 	- tomoyo_path_chown()
> > 	- smack_inode_getsecurity()
> > 	- smack_inode_setsecurity()
> 
> What's the bug? The file descriptor returned by open(O_PATH) cannot be
> passed to read(2), write(2), fchmod(2), fchown(2), fgetxattr(2), mmap(2) etc.
> 

chmod(2), chown(2), getxattr(2), and setxattr(2) take a path, not a fd.

- Eric

Re: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[Tetsuo Handa]

Eric Biggers wrote:
> On Thu, Aug 22, 2019 at 03:55:31PM +0900, Tetsuo Handa wrote:
> > > Also, isn't the same bug in other places too?:
> > > 
> > > 	- tomoyo_path_chmod()
> > > 	- tomoyo_path_chown()
> > > 	- smack_inode_getsecurity()
> > > 	- smack_inode_setsecurity()
> > 
> > What's the bug? The file descriptor returned by open(O_PATH) cannot be
> > passed to read(2), write(2), fchmod(2), fchown(2), fgetxattr(2), mmap(2) etc.
> > 
> 
> chmod(2), chown(2), getxattr(2), and setxattr(2) take a path, not a fd.
> 

OK. Then, is the correct fix

  inode_lock(inode);
  if (SOCKET_I(inode)->sk) {
    // Can access SOCKET_I(sock)->sk->*
  } else {
    // Already close()d. Don't touch.
  }
  inode_unlock(inode);

thanks to

  commit 6d8c50dcb029872b ("socket: close race condition between sock_close() and sockfs_setattr()")
  commit ff7b11aa481f682e ("net: socket: set sock->sk to NULL after calling proto_ops::release()")

changes?

Re: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.

[Eric Biggers]

On Thu, Aug 22, 2019 at 04:42:26PM +0900, Tetsuo Handa wrote:
> Eric Biggers wrote:
> > On Thu, Aug 22, 2019 at 03:55:31PM +0900, Tetsuo Handa wrote:
> > > > Also, isn't the same bug in other places too?:
> > > > 
> > > > 	- tomoyo_path_chmod()
> > > > 	- tomoyo_path_chown()
> > > > 	- smack_inode_getsecurity()
> > > > 	- smack_inode_setsecurity()
> > > 
> > > What's the bug? The file descriptor returned by open(O_PATH) cannot be
> > > passed to read(2), write(2), fchmod(2), fchown(2), fgetxattr(2), mmap(2) etc.
> > > 
> > 
> > chmod(2), chown(2), getxattr(2), and setxattr(2) take a path, not a fd.
> > 
> 
> OK. Then, is the correct fix
> 
>   inode_lock(inode);
>   if (SOCKET_I(inode)->sk) {
>     // Can access SOCKET_I(sock)->sk->*
>   } else {
>     // Already close()d. Don't touch.
>   }
>   inode_unlock(inode);
> 
> thanks to
> 
>   commit 6d8c50dcb029872b ("socket: close race condition between sock_close() and sockfs_setattr()")
>   commit ff7b11aa481f682e ("net: socket: set sock->sk to NULL after calling proto_ops::release()")
> 
> changes?

inode_lock() is already held during security_path_chmod(),
security_path_chown(), and security_inode_setxattr().
So you can't just take it again.

- Eric