syzbot reported a null-ptr-deref below [1] following a fault injection in netfs_alloc_subrequest(). [0] When netfs_alloc_subrequest() fails, subreq is NULL. Later, netfs_prepare_write() tries to initialize members of subreq(e.g., source), the issue in [1] is triggered. Let's handle the error of netfs_prepare_write() properly. [0] FAULT_INJECTION: forcing a failure. name failslab, interval 1, probability 0, space 0, times 0 Call Trace: netfs_alloc_subrequest+0x116/0x3f0 netfs_prepare_write+0x76/0x7b0 netfs_unbuffered_write+0x75c/0x2020 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 netfs_unbuffered_write_iter+0x442/0x720 v9fs_file_write_iter+0xbf/0x100 vfs_write+0x6ac/0x1050 [1] KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af] RIP: 0010:netfs_prepare_write+0xbc/0x7b0 fs/netfs/write_issue.c:173 Call Trace: netfs_unbuffered_write+0x75c/0x2020 fs/netfs/direct_write.c:111 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 fs/netfs/direct_write.c:290 netfs_unbuffered_write_iter+0x442/0x720 fs/netfs/direct_write.c:382 v9fs_file_write_iter+0xbf/0x100 fs/9p/vfs_file.c:409 new_sync_write fs/read_write.c:595 [inline] Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Reported-by: syzbot+6a13fc77eb6f0802be2d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6a13fc77eb6f0802be2d Tested-by: syzbot+6a13fc77eb6f0802be2d@syzkaller.appspotmail.com Signed-off-by: Edward Adam Davis --- fs/netfs/direct_write.c | 4 ++++ fs/netfs/write_issue.c | 2 ++ 2 files changed, 6 insertions(+) diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c index c16fbad286a1..567b946b7a56 100644 --- a/fs/netfs/direct_write.c +++ b/fs/netfs/direct_write.c @@ -110,6 +110,10 @@ static int netfs_unbuffered_write(struct netfs_io_request *wreq) if (!subreq) { netfs_prepare_write(wreq, stream, wreq->start + wreq->transferred); subreq = stream->construct; + if (!subreq) { + wreq->error = -ENOMEM; + break; + } stream->construct = NULL; } diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c index 2d9cfcd43658..851f6f93ad45 100644 --- a/fs/netfs/write_issue.c +++ b/fs/netfs/write_issue.c @@ -170,6 +170,8 @@ void netfs_prepare_write(struct netfs_io_request *wreq, rolling_buffer_make_space(&wreq->buffer, wreq->gfp); subreq = netfs_alloc_subrequest(wreq); + if (!subreq) + return; subreq->source = stream->source; subreq->start = start; subreq->stream_nr = stream->stream_nr; -- 2.43.0