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

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Date:   Tue, 10 Apr 2018 19:13:23 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     syzbot <syzbot+9369930ca44f29e60e2d@...kaller.appspotmail.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, viro@...iv.linux.org.uk
Subject: Re: KASAN: null-ptr-deref Read in xattr_getsecurity

>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

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