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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: [PATCH] tomoyo: Don't check open/getattr permission on sockets.
Date: Sun, 9 Jun 2019 15:41:18 +0900
Message-ID: <1b5722cc-adbc-035d-5ca1-9aa56e70d312@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <201906060520.x565Kd8j017983@www262.sakura.ne.jp>

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



  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-05 18:42 KASAN: use-after-free Read in tomoyo_realpath_from_path syzbot
2019-06-05 22:09 ` Tetsuo Handa
2019-06-06  2:08 ` Tetsuo Handa
2019-06-06  5:20 ` Tetsuo Handa
2019-06-09  6:41   ` Tetsuo Handa [this message]
2019-06-16  6:49     ` [PATCH] tomoyo: Don't check open/getattr permission on sockets Tetsuo Handa
2019-06-18 20:49       ` Al Viro
2019-06-22  4:45         ` [PATCH v2] " Tetsuo Handa
2019-07-04 11:58           ` Tetsuo Handa
2019-07-07  2:44             ` James Morris
2019-07-07  2:50               ` James Morris
2019-08-09 15:51                 ` Tetsuo Handa
2019-09-03  6:52                 ` Tetsuo Handa
2019-09-13 13:41                   ` Tetsuo Handa
     [not found]                     ` <A9CE5147-4047-4C42-B772-F0ED510FA283@canb.auug.org.au>
2019-10-02 10:50                       ` Tetsuo Handa
2019-10-02 22:25                         ` Stephen Rothwell
2019-10-03  9:59                           ` Tetsuo Handa
2019-11-13 13:49                             ` Tetsuo Handa
2019-10-02 22:22                     ` Stephen Rothwell
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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