From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Layton Subject: Re: [PATCH v2] ceph: Fix use-after-free in __ceph_remove_cap Date: Sun, 27 Oct 2019 08:31:49 -0400 Message-ID: <1a9ac7d3097efe53ad6f2fda4dd584204dd7eba2.camel@kernel.org> References: <9c1fe73500ca7dece15c73d7534b9e0ec417c83a.camel@kernel.org> <20191025130524.31755-1-lhenriques@suse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20191025130524.31755-1-lhenriques@suse.com> Sender: linux-kernel-owner@vger.kernel.org To: Luis Henriques , Sage Weil , Ilya Dryomov , "Yan, Zheng" Cc: ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: ceph-devel.vger.kernel.org On Fri, 2019-10-25 at 14:05 +0100, Luis Henriques wrote: > KASAN reports a use-after-free when running xfstest generic/531, with the > following trace: > > [ 293.903362] kasan_report+0xe/0x20 > [ 293.903365] rb_erase+0x1f/0x790 > [ 293.903370] __ceph_remove_cap+0x201/0x370 > [ 293.903375] __ceph_remove_caps+0x4b/0x70 > [ 293.903380] ceph_evict_inode+0x4e/0x360 > [ 293.903386] evict+0x169/0x290 > [ 293.903390] __dentry_kill+0x16f/0x250 > [ 293.903394] dput+0x1c6/0x440 > [ 293.903398] __fput+0x184/0x330 > [ 293.903404] task_work_run+0xb9/0xe0 > [ 293.903410] exit_to_usermode_loop+0xd3/0xe0 > [ 293.903413] do_syscall_64+0x1a0/0x1c0 > [ 293.903417] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > This happens because __ceph_remove_cap() may queue a cap release > (__ceph_queue_cap_release) which can be scheduled before that cap is > removed from the inode list with > > rb_erase(&cap->ci_node, &ci->i_caps); > > And, when this finally happens, the use-after-free will occur. > > This can be fixed by removing the cap from the inode list before being > removed from the session list, and thus eliminating the risk of an UAF. > > Signed-off-by: Luis Henriques > --- > Hi! > > So, after spending some time trying to find possible races throught code > review and testing, I modified the fix according to Jeff's suggestion. > > Cheers, > Luis > > fs/ceph/caps.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c > index d3b9c9d5c1bd..a9ce858c37d0 100644 > --- a/fs/ceph/caps.c > +++ b/fs/ceph/caps.c > @@ -1058,6 +1058,11 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release) > > dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode); > > + /* remove from inode list */ > + rb_erase(&cap->ci_node, &ci->i_caps); > + if (ci->i_auth_cap == cap) > + ci->i_auth_cap = NULL; > + > /* remove from session list */ > spin_lock(&session->s_cap_lock); > if (session->s_cap_iterator == cap) { > @@ -1091,11 +1096,6 @@ void __ceph_remove_cap(struct ceph_cap *cap, bool queue_release) > > spin_unlock(&session->s_cap_lock); > > - /* remove from inode list */ > - rb_erase(&cap->ci_node, &ci->i_caps); > - if (ci->i_auth_cap == cap) > - ci->i_auth_cap = NULL; > - > if (removed) > ceph_put_cap(mdsc, cap); > Looks good. Merged with a slight modification to the comment: + /* remove from inode's cap rbtree, and clear auth cap */ Thanks! -- Jeff Layton