[PATCH v2 06/12] cachefiles: add consistency check for copen/cread

[libaokun]

From: Baokun Li <libaok...@huawei.com>

This prevents malicious processes from completing random copen/cread
requests and crashing the system. Added checks are listed below:

  * Generic, copen can only complete open requests, and cread can only
    complete read requests.
  * For copen, ondemand_id must not be 0, because this indicates that the
    request has not been read by the daemon.
  * For cread, the object corresponding to fd and req should be the same.

Signed-off-by: Baokun Li <libaok...@huawei.com>
---
 fs/cachefiles/ondemand.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index bb94ef6a6f61..898fab68332b 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -82,12 +82,12 @@ static loff_t cachefiles_ondemand_fd_llseek(struct file 
*filp, loff_t pos,
 }
 
 static long cachefiles_ondemand_fd_ioctl(struct file *filp, unsigned int ioctl,
-                                        unsigned long arg)
+                                        unsigned long id)
 {
        struct cachefiles_object *object = filp->private_data;
        struct cachefiles_cache *cache = object->volume->cache;
        struct cachefiles_req *req;
-       unsigned long id;
+       XA_STATE(xas, &cache->reqs, id);
 
        if (ioctl != CACHEFILES_IOC_READ_COMPLETE)
                return -EINVAL;
@@ -95,10 +95,15 @@ static long cachefiles_ondemand_fd_ioctl(struct file *filp, 
unsigned int ioctl,
        if (!test_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags))
                return -EOPNOTSUPP;
 
-       id = arg;
-       req = xa_erase(&cache->reqs, id);
-       if (!req)
+       xa_lock(&cache->reqs);
+       req = xas_load(&xas);
+       if (!req || req->msg.opcode != CACHEFILES_OP_READ ||
+           req->object != object) {
+               xa_unlock(&cache->reqs);
                return -EINVAL;
+       }
+       xas_store(&xas, NULL);
+       xa_unlock(&cache->reqs);
 
        trace_cachefiles_ondemand_cread(object, id);
        complete(&req->done);
@@ -126,6 +131,7 @@ int cachefiles_ondemand_copen(struct cachefiles_cache 
*cache, char *args)
        unsigned long id;
        long size;
        int ret;
+       XA_STATE(xas, &cache->reqs, 0);
 
        if (!test_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags))
                return -EOPNOTSUPP;
@@ -149,9 +155,16 @@ int cachefiles_ondemand_copen(struct cachefiles_cache 
*cache, char *args)
        if (ret)
                return ret;
 
-       req = xa_erase(&cache->reqs, id);
-       if (!req)
+       xa_lock(&cache->reqs);
+       xas.xa_index = id;
+       req = xas_load(&xas);
+       if (!req || req->msg.opcode != CACHEFILES_OP_OPEN ||
+           !req->object->ondemand->ondemand_id) {
+               xa_unlock(&cache->reqs);
                return -EINVAL;
+       }
+       xas_store(&xas, NULL);
+       xa_unlock(&cache->reqs);
 
        /* fail OPEN request if copen format is invalid */
        ret = kstrtol(psize, 0, &size);
-- 
2.39.2