Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir

From: Xiubo Li
Date: Sat Mar 05 2022 - 07:43:23 EST



On 3/5/22 2:20 AM, Jeff Layton wrote:
On Fri, 2022-03-04 at 16:14 +0000, Luís Henriques wrote:
After calling ceph_mdsc_put_request() on dfi->last_readdir, this field
should be set to NULL, otherwise we may end-up freeing it twince and get
the following splat:

refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 229 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
...
Call Trace:
<TASK>
ceph_readdir+0xd35/0x1460 [ceph]
? _raw_spin_unlock+0x12/0x30
? preempt_count_add+0x73/0xa0
? _raw_spin_unlock+0x12/0x30
? __mark_inode_dirty+0x27c/0x3a0
iterate_dir+0x7d/0x190
__x64_sys_getdents64+0x80/0x120
? compat_fillonedir+0x160/0x160
do_syscall_64+0x43/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae

Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
---
fs/ceph/dir.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 0bcb677d2199..934402f5e9e6 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -555,6 +555,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
le32_to_cpu(rde->inode.in->mode) >> 12)) {
dout("filldir stopping us...\n");
ceph_mdsc_put_request(dfi->last_readdir);
+ dfi->last_readdir = NULL;
err = 0;
goto out;
}
I think Xiubo fixed this in the testing branch late yesterday. It should
no longer be needed.

Right and I have sent a new version of my previous patch to remove the buggy code.

- Xiubo

Thanks,