linux-kernel - Re: KASAN: null-ptr-deref Read in xattr

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Date:   Tue, 10 Apr 2018 09:42:50 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     syzbot <syzbot+9369930ca44f29e60e2d@...kaller.appspotmail.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk,
        <linux-security-module@...r.kernel.org>
Subject: Re: KASAN: null-ptr-deref Read in xattr_getsecurity

Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> writes:

> From 904d07a6eb014f3df0c5a1ebfcfd4323276a9a76 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Tue, 10 Apr 2018 15:15:16 +0900
> Subject: [PATCH] commoncap: Handle memory allocation failure.
>
> syzbot is reporting NULL pointer dereference at xattr_getsecurity() [1],
> for cap_inode_getsecurity() is returning sizeof(struct vfs_cap_data) when
> memory allocation failed. Return -ENOMEM if memory allocation failed.
>
> [1] https://syzkaller.appspot.com/bug?id=a55ba438506fe68649a5f50d2d82d56b365e0107

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Tetsuo I can pick this up, or do you have preferred path for getting
this change merged?

Serge does this fix look ok to you?  I am a bit worried that
might be a bit brittler but I don't see any issues with this change.

Eric


> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Fixes: 8db6c34f1dbc8e06 ("Introduce v3 namespaced file capabilities")
> Reported-by: syzbot <syzbot+9369930ca44f29e60e2d@...kaller.appspotmail.com>
> Cc: stable <stable@...r.kernel.org> # 4.14+
> Cc: Serge E. Hallyn <serge@...lyn.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> ---
>  security/commoncap.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 48620c9..1ce701f 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -449,6 +449,8 @@ int cap_inode_getsecurity(struct inode *inode, const char *name, void **buffer,
>  				magic |= VFS_CAP_FLAGS_EFFECTIVE;
>  			memcpy(&cap->data, &nscap->data, sizeof(__le32) * 2 * VFS_CAP_U32);
>  			cap->magic_etc = cpu_to_le32(magic);
> +		} else {
> +			size = -ENOMEM;
>  		}
>  	}
>  	kfree(tmpbuf);
> --
> 1.8.3.1