From owner-freebsd-bugs@freebsd.org Fri Mar 8 01:57:47 2019 Return-Path: Delivered-To: freebsd-bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 7BDF9152EA9F for ; Fri, 8 Mar 2019 01:57:47 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mailman.ysv.freebsd.org (mailman.ysv.freebsd.org [IPv6:2001:1900:2254:206a::50:5]) by mx1.freebsd.org (Postfix) with ESMTP id 116F685595 for ; Fri, 8 Mar 2019 01:57:47 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: by mailman.ysv.freebsd.org (Postfix) id C62A8152EA9D; Fri, 8 Mar 2019 01:57:46 +0000 (UTC) Delivered-To: bugs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A22C7152EA9C for ; Fri, 8 Mar 2019 01:57:46 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.ysv.freebsd.org (mxrelay.ysv.freebsd.org [IPv6:2001:1900:2254:206a::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.ysv.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 3FDF58558F for ; Fri, 8 Mar 2019 01:57:46 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.ysv.freebsd.org (Postfix) with ESMTPS id 88C031B9A5 for ; Fri, 8 Mar 2019 01:57:45 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id x281vjaZ086061 for ; Fri, 8 Mar 2019 01:57:45 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id x281vjGP086060 for bugs@FreeBSD.org; Fri, 8 Mar 2019 01:57:45 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 236381] [FUSE] EFAULT and possible data corruption with short writes Date: Fri, 08 Mar 2019 01:57:45 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Many People X-Bugzilla-Who: asomers@FreeBSD.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version rep_platform op_sys bug_status bug_severity priority component assigned_to reporter Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 08 Mar 2019 01:57:47 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D236381 Bug ID: 236381 Summary: [FUSE] EFAULT and possible data corruption with short writes Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Many People Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: asomers@FreeBSD.org Normally fuse filesystems are required to always write the exact amount of = data requested by a FUSE_WRITE operation. However, if the filesystem sets FOPEN_DIRECT_IO in the response to a FUSE_OPEN request, then it is allowed = to write less data than was requested. In that case, the client will likely w= ant to write the remainder of the data. The problem is that fuse_write_directbackend doesn't correctly account for = the short write. It correctly detects a short write, and tries to "rewind" the= uio by adjusting its uio_resid and uio_offset fields. However, it neglects to rewind the uio_iov field. In fact, it will not always be possible to rewind the uio_iov, because uiomove may have incremented the uio_iov pointer. I s= ee two possible solutions: 1) Add a second inner loop to fuse_write_directbackend. The inner loop will handle short writes, and will get its data from the fdi buffer. uiomove wi= ll not be called again. In addition to fixing the bug, this method will also = be more efficient than current code, because it won't copy data across the user-kernel boundary multiple times. 2) Don't try to make up for short writes. Simply return to userland. This would probably be more in the spirit of direct_io. However, fuse_write_directbackend can have many different callers, and it might not = be appropriate for all of them. In particular, fuse(4) currently doesn't accurately track whether the filesystem requested FOPEN_DIRECT_IO. --=20 You are receiving this mail because: You are the assignee for the bug.=