Patch "cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cachefiles-fix-slab-use-after-free-in-cachefiles_ond.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 209b422248ee51b76d4dab06cba3be99267585f1
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Wed May 22 19:43:00 2024 +0800

    cachefiles: fix slab-use-after-free in cachefiles_ondemand_daemon_read()
    
    [ Upstream commit da4a827416066191aafeeccee50a8836a826ba10 ]
    
    We got the following issue in a fuzz test of randomly issuing the restore
    command:
    
    ==================================================================
    BUG: KASAN: slab-use-after-free in cachefiles_ondemand_daemon_read+0xb41/0xb60
    Read of size 8 at addr ffff888122e84088 by task ondemand-04-dae/963
    
    CPU: 13 PID: 963 Comm: ondemand-04-dae Not tainted 6.8.0-dirty #564
    Call Trace:
     kasan_report+0x93/0xc0
     cachefiles_ondemand_daemon_read+0xb41/0xb60
     vfs_read+0x169/0xb50
     ksys_read+0xf5/0x1e0
    
    Allocated by task 116:
     kmem_cache_alloc+0x140/0x3a0
     cachefiles_lookup_cookie+0x140/0xcd0
     fscache_cookie_state_machine+0x43c/0x1230
     [...]
    
    Freed by task 792:
     kmem_cache_free+0xfe/0x390
     cachefiles_put_object+0x241/0x480
     fscache_cookie_state_machine+0x5c8/0x1230
     [...]
    ==================================================================
    
    Following is the process that triggers the issue:
    
         mount  |   daemon_thread1    |    daemon_thread2
    ------------------------------------------------------------
    cachefiles_withdraw_cookie
     cachefiles_ondemand_clean_object(object)
      cachefiles_ondemand_send_req
       REQ_A = kzalloc(sizeof(*req) + data_len)
       wait_for_completion(&REQ_A->done)
    
                cachefiles_daemon_read
                 cachefiles_ondemand_daemon_read
                  REQ_A = cachefiles_ondemand_select_req
                  msg->object_id = req->object->ondemand->ondemand_id
                                      ------ restore ------
                                      cachefiles_ondemand_restore
                                      xas_for_each(&xas, req, ULONG_MAX)
                                       xas_set_mark(&xas, CACHEFILES_REQ_NEW)
    
                                      cachefiles_daemon_read
                                       cachefiles_ondemand_daemon_read
                                        REQ_A = cachefiles_ondemand_select_req
                  copy_to_user(_buffer, msg, n)
                   xa_erase(&cache->reqs, id)
                   complete(&REQ_A->done)
                  ------ close(fd) ------
                  cachefiles_ondemand_fd_release
                   cachefiles_put_object
     cachefiles_put_object
      kmem_cache_free(cachefiles_object_jar, object)
                                        REQ_A->object->ondemand->ondemand_id
                                         // object UAF !!!
    
    When we see the request within xa_lock, req->object must not have been
    freed yet, so grab the reference count of object before xa_unlock to
    avoid the above issue.
    
    Fixes: 0a7e54c1959c ("cachefiles: resend an open request if the read request's object is closed")
    Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240522114308.2402121-5-libaokun@xxxxxxxxxxxxxxx
    Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
    Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
    Stable-dep-of: 4b4391e77a6b ("cachefiles: defer exposing anon_fd until after copy_to_user() succeeds")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index f8d0a01795702..fd73811c7ce4f 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -369,6 +369,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 	xas_clear_mark(&xas, CACHEFILES_REQ_NEW);
 	cache->req_id_next = xas.xa_index + 1;
 	refcount_inc(&req->ref);
+	cachefiles_grab_object(req->object, cachefiles_obj_get_read_req);
 	xa_unlock(&cache->reqs);
 
 	id = xas.xa_index;
@@ -389,6 +390,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 		goto err_put_fd;
 	}
 
+	cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
 	/* CLOSE request has no reply */
 	if (msg->opcode == CACHEFILES_OP_CLOSE) {
 		xa_erase(&cache->reqs, id);
@@ -402,6 +404,7 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 	if (msg->opcode == CACHEFILES_OP_OPEN)
 		close_fd(((struct cachefiles_open *)msg->data)->fd);
 error:
+	cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
 	xas_reset(&xas);
 	xas_lock(&xas);
 	if (xas_load(&xas) == req) {
diff --git a/include/trace/events/cachefiles.h b/include/trace/events/cachefiles.h
index b4939097f5116..dff9a48502247 100644
--- a/include/trace/events/cachefiles.h
+++ b/include/trace/events/cachefiles.h
@@ -33,6 +33,8 @@ enum cachefiles_obj_ref_trace {
 	cachefiles_obj_see_withdrawal,
 	cachefiles_obj_get_ondemand_fd,
 	cachefiles_obj_put_ondemand_fd,
+	cachefiles_obj_get_read_req,
+	cachefiles_obj_put_read_req,
 };
 
 enum fscache_why_object_killed {
@@ -129,7 +131,9 @@ enum cachefiles_error_trace {
 	EM(cachefiles_obj_see_withdraw_cookie,	"SEE withdraw_cookie")	\
 	EM(cachefiles_obj_see_withdrawal,	"SEE withdrawal")	\
 	EM(cachefiles_obj_get_ondemand_fd,      "GET ondemand_fd")	\
-	E_(cachefiles_obj_put_ondemand_fd,      "PUT ondemand_fd")
+	EM(cachefiles_obj_put_ondemand_fd,      "PUT ondemand_fd")	\
+	EM(cachefiles_obj_get_read_req,		"GET read_req")		\
+	E_(cachefiles_obj_put_read_req,		"PUT read_req")
 
 #define cachefiles_coherency_traces					\
 	EM(cachefiles_coherency_check_aux,	"BAD aux ")		\




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