The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Thanks, Sasha
------------------ original commit in Linus's tree ------------------
From 17f46b803d4f23c66cacce81db35fef3adb8f2af Mon Sep 17 00:00:00 2001 From: Josef Bacik josef@toxicpanda.com Date: Fri, 1 Mar 2024 11:49:57 -0500 Subject: [PATCH] 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: <TASK> ? __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.
Signed-off-by: Josef Bacik josef@toxicpanda.com Cc: stable@vger.kernel.org Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com --- fs/nfs/direct.c | 11 +++++++++-- fs/nfs/write.c | 2 +- include/linux/nfs_fs.h | 1 + 3 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c index befcc167e25fe..6b8798d01e3a1 100644 --- a/fs/nfs/direct.c +++ b/fs/nfs/direct.c @@ -672,10 +672,17 @@ static void nfs_direct_commit_schedule(struct nfs_direct_req *dreq) LIST_HEAD(mds_list);
nfs_init_cinfo_from_dreq(&cinfo, dreq); + nfs_commit_begin(cinfo.mds); nfs_scan_commit(dreq->inode, &mds_list, &cinfo); res = nfs_generic_commit_list(dreq->inode, &mds_list, 0, &cinfo); - if (res < 0) /* res == -ENOMEM */ - nfs_direct_write_reschedule(dreq); + if (res < 0) { /* res == -ENOMEM */ + spin_lock(&dreq->lock); + if (dreq->flags == 0) + dreq->flags = NFS_ODIRECT_RESCHED_WRITES; + spin_unlock(&dreq->lock); + } + if (nfs_commit_end(cinfo.mds)) + nfs_direct_write_complete(dreq); }
static void nfs_direct_write_clear_reqs(struct nfs_direct_req *dreq) diff --git a/fs/nfs/write.c b/fs/nfs/write.c index 58adbb7709ba7..15359bbfa56bc 100644 --- a/fs/nfs/write.c +++ b/fs/nfs/write.c @@ -1646,7 +1646,7 @@ static int wait_on_commit(struct nfs_mds_commit_info *cinfo) !atomic_read(&cinfo->rpcs_out)); }
-static void nfs_commit_begin(struct nfs_mds_commit_info *cinfo) +void nfs_commit_begin(struct nfs_mds_commit_info *cinfo) { atomic_inc(&cinfo->rpcs_out); } diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h index f5ce7b1011461..d59116ac82099 100644 --- a/include/linux/nfs_fs.h +++ b/include/linux/nfs_fs.h @@ -611,6 +611,7 @@ int nfs_wb_folio_cancel(struct inode *inode, struct folio *folio); extern int nfs_commit_inode(struct inode *, int); extern struct nfs_commit_data *nfs_commitdata_alloc(void); extern void nfs_commit_free(struct nfs_commit_data *data); +void nfs_commit_begin(struct nfs_mds_commit_info *cinfo); bool nfs_commit_end(struct nfs_mds_commit_info *cinfo);
static inline bool nfs_have_writebacks(const struct inode *inode)