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Date: Mon, 21 Nov 2022 11:48:40 -0800 From: Andrew Morton <akpm@...ux-foundation.org> To: Alexander Potapenko <glider@...gle.com> Cc: linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, jaegeuk@...nel.org, chao@...nel.org, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, Eric Biggers <ebiggers@...nel.org>, syzbot+9767be679ef5016b6082@...kaller.appspotmail.com Subject: Re: [PATCH 1/5] fs: ext4: initialize fsdata in pagecache_write() On Mon, 21 Nov 2022 12:21:30 +0100 Alexander Potapenko <glider@...gle.com> wrote: > When aops->write_begin() does not initialize fsdata, KMSAN reports > an error passing the latter to aops->write_end(). > > Fix this by unconditionally initializing fsdata. > > ... > I'm assuming that this is not-a-bug, and that these changes are purely workarounds for a KMSAN shortcoming? If true, this important info should be included in each changelog, please. If false, please provide a full description of the end-user visible effects of the bug. Also, it would be helpful to describe why it is not considered practical to teach KMSAN to handle this? > --- a/fs/ext4/verity.c > +++ b/fs/ext4/verity.c > @@ -79,7 +79,7 @@ static int pagecache_write(struct inode *inode, const void *buf, size_t count, > size_t n = min_t(size_t, count, > PAGE_SIZE - offset_in_page(pos)); > struct page *page; > - void *fsdata; > + void *fsdata = NULL; > int res; > > res = aops->write_begin(NULL, mapping, pos, n, &page, &fsdata);
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