archive mirror
 help / color / mirror / Atom feed
From: Tetsuo Handa <>
To: Al Viro <>
	syzbot <>,,,,,,,
	"David S. Miller" <>
Subject: [PATCH v2] tomoyo: Don't check open/getattr permission on sockets.
Date: Sat, 22 Jun 2019 13:45:30 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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 <>
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.


Signed-off-by: Tetsuo Handa <>
Reported-by: syzbot <>
 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,

  reply	other threads:[~2019-06-22  4:46 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2019-06-06  2:08 ` KASAN: use-after-free Read in tomoyo_realpath_from_path Tetsuo Handa
2019-06-06  5:20 ` 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         ` Tetsuo Handa [this message]
2019-08-22  6:30           ` [PATCH v2] " 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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).