From: Miklos Szeredi Date: Tue, 2 Nov 2021 10:10:37 +0000 (+0100) Subject: fuse: fix page stealing X-Git-Tag: v6.6.17~8874^2 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=712a951025c0667ff00b25afc360f74e639dfabe;p=platform%2Fkernel%2Flinux-rpi.git fuse: fix page stealing It is possible to trigger a crash by splicing anon pipe bufs to the fuse device. The reason for this is that anon_pipe_buf_release() will reuse buf->page if the refcount is 1, but that page might have already been stolen and its flags modified (e.g. PG_lru added). This happens in the unlikely case of fuse_dev_splice_write() getting around to calling pipe_buf_release() after a page has been stolen, added to the page cache and removed from the page cache. Fix by calling pipe_buf_release() right after the page was inserted into the page cache. In this case the page has an elevated refcount so any release function will know that the page isn't reusable. Reported-by: Frank Dinoff Link: https://lore.kernel.org/r/CAAmZXrsGg2xsP1CK+cbuEMumtrqdvD-NKnWzhNcvn71RV3c1yw@mail.gmail.com/ Fixes: dd3bb14f44a6 ("fuse: support splice() writing to fuse device") Cc: # v2.6.35 Signed-off-by: Miklos Szeredi --- diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 337fa6f..79f7eda 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -847,6 +847,12 @@ static int fuse_try_move_page(struct fuse_copy_state *cs, struct page **pagep) replace_page_cache_page(oldpage, newpage); + /* + * Release while we have extra ref on stolen page. Otherwise + * anon_pipe_buf_release() might think the page can be reused. + */ + pipe_buf_release(cs->pipe, buf); + get_page(newpage); if (!(buf->flags & PIPE_BUF_FLAG_LRU)) @@ -2031,8 +2037,12 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe, pipe_lock(pipe); out_free: - for (idx = 0; idx < nbuf; idx++) - pipe_buf_release(pipe, &bufs[idx]); + for (idx = 0; idx < nbuf; idx++) { + struct pipe_buffer *buf = &bufs[idx]; + + if (buf->ops) + pipe_buf_release(pipe, buf); + } pipe_unlock(pipe); kvfree(bufs);