6.6-stable review patch. If anyone has any objections, please let me know.
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From: Baokun Li libaokun1@huawei.com
[ Upstream commit 19f4f399091478c95947f6bd7ad61622300c30d9 ]
Reusing the msg_id after a maliciously completed reopen request may cause a read request to remain unprocessed and result in a hung, as shown below:
t1 | t2 | t3 ------------------------------------------------- cachefiles_ondemand_select_req cachefiles_ondemand_object_is_close(A) cachefiles_ondemand_set_object_reopening(A) queue_work(fscache_object_wq, &info->work) ondemand_object_worker cachefiles_ondemand_init_object(A) cachefiles_ondemand_send_req(OPEN) // get msg_id 6 wait_for_completion(&req_A->done) cachefiles_ondemand_daemon_read // read msg_id 6 req_A cachefiles_ondemand_get_fd copy_to_user // Malicious completion msg_id 6 copen 6,-1 cachefiles_ondemand_copen complete(&req_A->done) // will not set the object to close // because ondemand_id && fd is valid.
// ondemand_object_worker() is done // but the object is still reopening.
// new open req_B cachefiles_ondemand_init_object(B) cachefiles_ondemand_send_req(OPEN) // reuse msg_id 6 process_open_req copen 6,A.size // The expected failed copen was executed successfully
Expect copen to fail, and when it does, it closes fd, which sets the object to close, and then close triggers reopen again. However, due to msg_id reuse resulting in a successful copen, the anonymous fd is not closed until the daemon exits. Therefore read requests waiting for reopen to complete may trigger hung task.
To avoid this issue, allocate the msg_id cyclically to avoid reusing the msg_id for a very short duration of time.
Fixes: c8383054506c ("cachefiles: notify the user daemon when looking up cookie") Signed-off-by: Baokun Li libaokun1@huawei.com Link: https://lore.kernel.org/r/20240628062930.2467993-9-libaokun@huaweicloud.com Acked-by: Jeff Layton jlayton@kernel.org Reviewed-by: Gao Xiang hsiangkao@linux.alibaba.com Reviewed-by: Jia Zhu zhujia.zj@bytedance.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/cachefiles/internal.h | 1 + fs/cachefiles/ondemand.c | 20 ++++++++++++++++---- 2 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h index 94f59123726ca..111ad6ecd4baf 100644 --- a/fs/cachefiles/internal.h +++ b/fs/cachefiles/internal.h @@ -129,6 +129,7 @@ struct cachefiles_cache { unsigned long req_id_next; struct xarray ondemand_ids; /* xarray for ondemand_id allocation */ u32 ondemand_id_next; + u32 msg_id_next; };
static inline bool cachefiles_in_ondemand_mode(struct cachefiles_cache *cache) diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c index 1f6561814e702..51173ab6dbd84 100644 --- a/fs/cachefiles/ondemand.c +++ b/fs/cachefiles/ondemand.c @@ -505,20 +505,32 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object, smp_mb();
if (opcode == CACHEFILES_OP_CLOSE && - !cachefiles_ondemand_object_is_open(object)) { + !cachefiles_ondemand_object_is_open(object)) { WARN_ON_ONCE(object->ondemand->ondemand_id == 0); xas_unlock(&xas); ret = -EIO; goto out; }
- xas.xa_index = 0; + /* + * Cyclically find a free xas to avoid msg_id reuse that would + * cause the daemon to successfully copen a stale msg_id. + */ + xas.xa_index = cache->msg_id_next; xas_find_marked(&xas, UINT_MAX, XA_FREE_MARK); + if (xas.xa_node == XAS_RESTART) { + xas.xa_index = 0; + xas_find_marked(&xas, cache->msg_id_next - 1, XA_FREE_MARK); + } if (xas.xa_node == XAS_RESTART) xas_set_err(&xas, -EBUSY); + xas_store(&xas, req); - xas_clear_mark(&xas, XA_FREE_MARK); - xas_set_mark(&xas, CACHEFILES_REQ_NEW); + if (xas_valid(&xas)) { + cache->msg_id_next = xas.xa_index + 1; + xas_clear_mark(&xas, XA_FREE_MARK); + xas_set_mark(&xas, CACHEFILES_REQ_NEW); + } xas_unlock(&xas); } while (xas_nomem(&xas, GFP_KERNEL));