CVE-2024-26958 Information

Description

In the Linux kernel the following vulnerability has been resolved:

nfs: fix UAF in direct writes

In production we have been hitting the following warning consistently

————[ cut here ]———— refcount_t: underflow; use-after-free. WARNING: CPU: 17 PID: 1800359 at lib/refcount.c:28 refcount_warn_saturate+0x9c/0xe0 Workqueue: nfsiod nfs_direct_write_schedule_work [nfs] RIP: 0010:refcount_warn_saturate+0x9c/0xe0 PKRU: 55555554 Call Trace: ? __warn+0x9f/0x130 ? refcount_warn_saturate+0x9c/0xe0 ? report_bug+0xcc/0x150 ? handle_bug+0x3d/0x70 ? exc_invalid_op+0x16/0x40 ? asm_exc_invalid_op+0x16/0x20 ? refcount_warn_saturate+0x9c/0xe0 nfs_direct_write_schedule_work+0x237/0x250 [nfs] process_one_work+0x12f/0x4a0 worker_thread+0x14e/0x3b0 ? ZSTD_getCParams_internal+0x220/0x220 kthread+0xdc/0x120 ? __btf_name_valid+0xa0/0xa0 ret_from_fork+0x1f/0x30

This is because we’re completing the nfs_direct_request twice in a row.

The source of this is when we have our commit requests to submit we process them and send them off and then in the completion path for the commit requests we have

if (nfs_commit_end(cinfo.mds)) nfs_direct_write_complete(dreq);

However since we’re submitting asynchronous requests we sometimes have one that completes before we submit the next one so we end up calling complete on the nfs_direct_request twice.

The only other place we use nfs_generic_commit_list() is in __nfs_commit_inode which wraps this call in a

nfs_commit_begin(); nfs_commit_end();

Which is a common pattern for this style of completion handling one that is also repeated in the direct code with get_dreq()/put_dreq() calls around where we process events as well as in the completion paths.

Fix this by using the same pattern for the commit requests.

Before with my 200 node rocksdb stress running this warning would pop every 10ish minutes. With my patch the stress test has been running for several hours without popping.

Reference

https://git.kernel.org/stable/c/4595d90b5d2ea5fa4d318d13f59055aa4bf3e7f5 https://git.kernel.org/stable/c/80d24b308b7ee7037fc90d8ac99f6f78df0a256f https://git.kernel.org/stable/c/3abc2d160ed8213948b147295d77d44a22c88fa3 https://git.kernel.org/stable/c/e25447c35f8745337ea8bc0c9697fcac14df8605 https://git.kernel.org/stable/c/1daf52b5ffb24870fbeda20b4967526d8f9e12ab https://git.kernel.org/stable/c/cf54f66e1dd78990ec6b32177bca7e6ea2144a95 https://git.kernel.org/stable/c/17f46b803d4f23c66cacce81db35fef3adb8f2af