| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-40899: cachefiles: fix slab-use-after-free in cachefiles_ondemand_get_fd() |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| cachefiles: fix slab-use-after-free in cachefiles_ondemand_get_fd() |
| |
| 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. |
| |
| The Linux kernel CVE team has assigned CVE-2024-40899 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.8 with commit e73fa11a356ca0905c3cc648eaacc6f0f2d2c8b3 and fixed in 6.9.6 with commit 1d902d9a3aa4f2a8bda698294e34be788be012fc |
| Issue introduced in 6.8 with commit e73fa11a356ca0905c3cc648eaacc6f0f2d2c8b3 and fixed in 6.10 with commit de3e26f9e5b76fc628077578c001c4a51bf54d06 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2024-40899 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| fs/cachefiles/internal.h |
| fs/cachefiles/ondemand.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/99e9c5bd27ddefa0f9db88625bf5e31c1e833d62 |
| https://git.kernel.org/stable/c/a6de82765e12fb1201ab607f0d3ffe3309b30fc0 |
| https://git.kernel.org/stable/c/1d902d9a3aa4f2a8bda698294e34be788be012fc |
| https://git.kernel.org/stable/c/de3e26f9e5b76fc628077578c001c4a51bf54d06 |
