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Message-Id: <20221201033310.18589-1-schspa@gmail.com>
Date: Thu, 1 Dec 2022 11:33:10 +0800
From: Schspa Shi <schspa@...il.com>
To: ericvh@...il.com, lucho@...kov.net, asmadeus@...ewreck.org,
linux_oss@...debyte.com, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com
Cc: v9fs-developer@...ts.sourceforge.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, Schspa Shi <schspa@...il.com>,
syzbot+8f1060e2aaf8ca55220b@...kaller.appspotmail.com
Subject: [PATCH v3] 9p/fd: set req refcount to zero to avoid uninitialized usage
When the new request allocated, the refcount will be zero if it is resued
one. But if the request is newly allocated from slab, it is not fully
initialized before add it to idr.
If the p9_read_work got a response before the refcount initiated. It will
use a uninitialized req, which will result in a bad request data struct.
Here is the logs from syzbot.
Corrupted memory at 0xffff88807eade00b [ 0xff 0x07 0x00 0x00 0x00 0x00
0x00 0x00 . . . . . . . . ] (in kfence-#110):
p9_fcall_fini net/9p/client.c:248 [inline]
p9_req_put net/9p/client.c:396 [inline]
p9_req_put+0x208/0x250 net/9p/client.c:390
p9_client_walk+0x247/0x540 net/9p/client.c:1165
clone_fid fs/9p/fid.h:21 [inline]
v9fs_fid_xattr_set+0xe4/0x2b0 fs/9p/xattr.c:118
v9fs_xattr_set fs/9p/xattr.c:100 [inline]
v9fs_xattr_handler_set+0x6f/0x120 fs/9p/xattr.c:159
__vfs_setxattr+0x119/0x180 fs/xattr.c:182
__vfs_setxattr_noperm+0x129/0x5f0 fs/xattr.c:216
__vfs_setxattr_locked+0x1d3/0x260 fs/xattr.c:277
vfs_setxattr+0x143/0x340 fs/xattr.c:309
setxattr+0x146/0x160 fs/xattr.c:617
path_setxattr+0x197/0x1c0 fs/xattr.c:636
__do_sys_setxattr fs/xattr.c:652 [inline]
__se_sys_setxattr fs/xattr.c:648 [inline]
__ia32_sys_setxattr+0xc0/0x160 fs/xattr.c:648
do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline]
__do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178
do_fast_syscall_32+0x33/0x70 arch/x86/entry/common.c:203
entry_SYSENTER_compat_after_hwframe+0x70/0x82
Below is a similar scenario, the scenario in the syzbot log looks more
complicated than this one, but this patch can fix it.
T21124 p9_read_work
======================== second trans =================================
p9_client_walk
p9_client_rpc
p9_client_prepare_req
p9_tag_alloc
req = kmem_cache_alloc(p9_req_cache, GFP_NOFS);
tag = idr_alloc
<< preempted >>
req->tc.tag = tag;
/* req->[refcount/tag] == uninitialized */
m->rreq = p9_tag_lookup(m->client, m->rc.tag);
/* increments uninitalized refcount */
refcount_set(&req->refcount, 2);
/* cb drops one ref */
p9_client_cb(req)
/* reader thread drops its ref:
request is incorrectly freed */
p9_req_put(req)
/* use after free and ref underflow */
p9_req_put(req)
To fix it, we can initize the refcount to zero before add to idr.
Reported-by: syzbot+8f1060e2aaf8ca55220b@...kaller.appspotmail.com
Signed-off-by: Schspa Shi <schspa@...il.com>
--
Changelog:
v1 -> v2:
- Set refcount to fix the problem.
v2 -> v3:
- Comment messages improve as asmadeus suggested.
---
net/9p/client.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/net/9p/client.c b/net/9p/client.c
index aaa37b07e30a..ec74cd29d3bc 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -297,6 +297,11 @@ p9_tag_alloc(struct p9_client *c, int8_t type, uint t_size, uint r_size,
p9pdu_reset(&req->rc);
req->t_err = 0;
req->status = REQ_STATUS_ALLOC;
+ /* refcount needs to be set to 0 before inserting into the idr
+ * so p9_tag_lookup does not accept a request that is not fully
+ * initialized. refcount_set to 2 below will mark request live.
+ */
+ refcount_set(&req->refcount, 0);
init_waitqueue_head(&req->wq);
INIT_LIST_HEAD(&req->req_list);
--
2.37.3
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