From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Al Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org
Cc: syzbot <syzbot+0341f6a4d729d4e0acf1@syzkaller.appspotmail.com>,
jmorris@namei.org, linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org, serge@hallyn.com,
syzkaller-bugs@googlegroups.com, takedakn@nttdata.co.jp
Subject: Re: KASAN: use-after-free Read in tomoyo_realpath_from_path
Date: Thu, 06 Jun 2019 11:08:29 +0900 [thread overview]
Message-ID: <201906060208.x5628T0g064822@www262.sakura.ne.jp> (raw)
In-Reply-To: <0000000000004f43fa058a97f4d3@google.com>
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
----------------------------------------
next parent reply other threads:[~2019-06-06 2:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0000000000004f43fa058a97f4d3@google.com>
2019-06-06 2:08 ` Tetsuo Handa [this message]
2019-06-06 5:20 ` KASAN: use-after-free Read in tomoyo_realpath_from_path Tetsuo Handa
2019-06-09 6:41 ` [PATCH] tomoyo: Don't check open/getattr permission on sockets Tetsuo Handa
2019-06-16 6:49 ` Tetsuo Handa
2019-06-18 20:49 ` Al Viro
2019-06-22 4:45 ` [PATCH v2] " Tetsuo Handa
2019-08-22 6:30 ` Eric Biggers
2019-08-22 6:55 ` Tetsuo Handa
2019-08-22 7:01 ` Eric Biggers
2019-08-22 7:42 ` Tetsuo Handa
2019-08-22 15:47 ` Eric Biggers
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