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 de3e26f9e5b76fc628077578c001c4a51bf54d06 ]
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+0x609/0xab0 Write of size 4 at addr ffff888109164a80 by task ondemand-04-dae/4962
CPU: 11 PID: 4962 Comm: ondemand-04-dae Not tainted 6.8.0-rc7-dirty #542 Call Trace: kasan_report+0x94/0xc0 cachefiles_ondemand_daemon_read+0x609/0xab0 vfs_read+0x169/0xb50 ksys_read+0xf5/0x1e0
Allocated by task 626: __kmalloc+0x1df/0x4b0 cachefiles_ondemand_send_req+0x24d/0x690 cachefiles_create_tmpfile+0x249/0xb30 cachefiles_create_file+0x6f/0x140 cachefiles_look_up_object+0x29c/0xa60 cachefiles_lookup_cookie+0x37d/0xca0 fscache_cookie_state_machine+0x43c/0x1230 [...]
Freed by task 626: kfree+0xf1/0x2c0 cachefiles_ondemand_send_req+0x568/0x690 cachefiles_create_tmpfile+0x249/0xb30 cachefiles_create_file+0x6f/0x140 cachefiles_look_up_object+0x29c/0xa60 cachefiles_lookup_cookie+0x37d/0xca0 fscache_cookie_state_machine+0x43c/0x1230 [...] ==================================================================
Following is the process that triggers the issue:
mount | daemon_thread1 | daemon_thread2 ------------------------------------------------------------ cachefiles_ondemand_init_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 cachefiles_ondemand_get_fd copy_to_user(_buffer, msg, n) process_open_req(REQ_A) ------ 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
write(devfd, ("copen %u,%llu", msg->msg_id, size)); cachefiles_ondemand_copen xa_erase(&cache->reqs, id) complete(&REQ_A->done) kfree(REQ_A) cachefiles_ondemand_get_fd(REQ_A) fd = get_unused_fd_flags file = anon_inode_getfile fd_install(fd, file) load = (void *)REQ_A->msg.data; load->fd = fd; // load UAF !!!
This issue is caused by issuing a restore command when the daemon is still alive, which results in a request being processed multiple times thus triggering a UAF. So to avoid this problem, add an additional reference count to cachefiles_req, which is held while waiting and reading, and then released when the waiting and reading is over.
Note that since there is only one reference count for waiting, we need to avoid the same request being completed multiple times, so we can only complete the request if it is successfully removed from the xarray.
Fixes: e73fa11a356c ("cachefiles: add restore command to recover inflight ondemand read requests") Suggested-by: Hou Tao houtao1@huawei.com Signed-off-by: Baokun Li libaokun1@huawei.com Link: https://lore.kernel.org/r/20240522114308.2402121-4-libaokun@huaweicloud.com Acked-by: Jeff Layton jlayton@kernel.org Reviewed-by: Jia Zhu zhujia.zj@bytedance.com Reviewed-by: Jingbo Xu jefflexu@linux.alibaba.com Signed-off-by: Christian Brauner brauner@kernel.org Stable-dep-of: 4b4391e77a6b ("cachefiles: defer exposing anon_fd until after copy_to_user() succeeds") Signed-off-by: Sasha Levin sashal@kernel.org --- fs/cachefiles/internal.h | 1 + fs/cachefiles/ondemand.c | 23 +++++++++++++++++++---- 2 files changed, 20 insertions(+), 4 deletions(-)
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h index 361356d0e866a..28799c8e2c6f6 100644 --- a/fs/cachefiles/internal.h +++ b/fs/cachefiles/internal.h @@ -139,6 +139,7 @@ static inline bool cachefiles_in_ondemand_mode(struct cachefiles_cache *cache) struct cachefiles_req { struct cachefiles_object *object; struct completion done; + refcount_t ref; int error; struct cachefiles_msg msg; }; diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c index 6d8f7f01a73ac..f8d0a01795702 100644 --- a/fs/cachefiles/ondemand.c +++ b/fs/cachefiles/ondemand.c @@ -4,6 +4,12 @@ #include <linux/uio.h> #include "internal.h"
+static inline void cachefiles_req_put(struct cachefiles_req *req) +{ + if (refcount_dec_and_test(&req->ref)) + kfree(req); +} + static int cachefiles_ondemand_fd_release(struct inode *inode, struct file *file) { @@ -362,6 +368,7 @@ 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); xa_unlock(&cache->reqs);
id = xas.xa_index; @@ -388,15 +395,22 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache, complete(&req->done); }
+ cachefiles_req_put(req); return n;
err_put_fd: if (msg->opcode == CACHEFILES_OP_OPEN) close_fd(((struct cachefiles_open *)msg->data)->fd); error: - xa_erase(&cache->reqs, id); - req->error = ret; - complete(&req->done); + xas_reset(&xas); + xas_lock(&xas); + if (xas_load(&xas) == req) { + req->error = ret; + complete(&req->done); + xas_store(&xas, NULL); + } + xas_unlock(&xas); + cachefiles_req_put(req); return ret; }
@@ -427,6 +441,7 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object, goto out; }
+ refcount_set(&req->ref, 1); req->object = object; init_completion(&req->done); req->msg.opcode = opcode; @@ -488,7 +503,7 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object, wake_up_all(&cache->daemon_pollwq); wait_for_completion(&req->done); ret = req->error; - kfree(req); + cachefiles_req_put(req); return ret; out: /* Reset the object to close state in error handling path.