6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Baokun Li <libaokun1@xxxxxxxxxx> [ 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> --- fs/cachefiles/ondemand.c | 3 +++ include/trace/events/cachefiles.h | 6 +++++- 2 files changed, 8 insertions(+), 1 deletion(-) 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 e3213af847cdf..7d931db02b934 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 ") \ -- 2.43.0