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Message-Id: <20201031113502.812234126@linuxfoundation.org> Date: Sat, 31 Oct 2020 12:36:40 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Pradeep P V K <ppvk@...eaurora.org>, Miklos Szeredi <mszeredi@...hat.com> Subject: [PATCH 5.9 58/74] fuse: fix page dereference after free From: Miklos Szeredi <mszeredi@...hat.com> commit d78092e4937de9ce55edcb4ee4c5e3c707be0190 upstream. After unlock_request() pages from the ap->pages[] array may be put (e.g. by aborting the connection) and the pages can be freed. Prevent use after free by grabbing a reference to the page before calling unlock_request(). The original patch was created by Pradeep P V K. Reported-by: Pradeep P V K <ppvk@...eaurora.org> Cc: <stable@...r.kernel.org> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- fs/fuse/dev.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-) --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -785,15 +785,16 @@ static int fuse_try_move_page(struct fus struct page *newpage; struct pipe_buffer *buf = cs->pipebufs; + get_page(oldpage); err = unlock_request(cs->req); if (err) - return err; + goto out_put_old; fuse_copy_finish(cs); err = pipe_buf_confirm(cs->pipe, buf); if (err) - return err; + goto out_put_old; BUG_ON(!cs->nr_segs); cs->currbuf = buf; @@ -833,7 +834,7 @@ static int fuse_try_move_page(struct fus err = replace_page_cache_page(oldpage, newpage, GFP_KERNEL); if (err) { unlock_page(newpage); - return err; + goto out_put_old; } get_page(newpage); @@ -852,14 +853,19 @@ static int fuse_try_move_page(struct fus if (err) { unlock_page(newpage); put_page(newpage); - return err; + goto out_put_old; } unlock_page(oldpage); + /* Drop ref for ap->pages[] array */ put_page(oldpage); cs->len = 0; - return 0; + err = 0; +out_put_old: + /* Drop ref obtained in this function */ + put_page(oldpage); + return err; out_fallback_unlock: unlock_page(newpage); @@ -868,10 +874,10 @@ out_fallback: cs->offset = buf->offset; err = lock_request(cs->req); - if (err) - return err; + if (!err) + err = 1; - return 1; + goto out_put_old; } static int fuse_ref_page(struct fuse_copy_state *cs, struct page *page, @@ -883,14 +889,16 @@ static int fuse_ref_page(struct fuse_cop if (cs->nr_segs >= cs->pipe->max_usage) return -EIO; + get_page(page); err = unlock_request(cs->req); - if (err) + if (err) { + put_page(page); return err; + } fuse_copy_finish(cs); buf = cs->pipebufs; - get_page(page); buf->page = page; buf->offset = offset; buf->len = count;
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