Date: Wed, 2 Dec 2015 21:47:43 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Mateusz Guzik <mjguzik@gmail.com> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r291481 - head/sys/compat/linuxkpi/common/include/linux Message-ID: <565F58EF.1030707@selasky.org> In-Reply-To: <20151202202958.GA30250@dft-labs.eu> References: <201511300924.tAU9OC7o049788@repo.freebsd.org> <20151202202958.GA30250@dft-labs.eu>
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On 12/02/15 21:29, Mateusz Guzik wrote: > On Mon, Nov 30, 2015 at 09:24:12AM +0000, Hans Petter Selasky wrote: >> Author: hselasky >> Date: Mon Nov 30 09:24:12 2015 >> New Revision: 291481 >> URL: https://svnweb.freebsd.org/changeset/base/291481 >> >> Log: >> Add more functions and types to the LinuxKPI. >> >> MFC after: 1 week >> Sponsored by: Mellanox Technologies >> >> Modified: >> head/sys/compat/linuxkpi/common/include/linux/file.h >> head/sys/compat/linuxkpi/common/include/linux/workqueue.h >> >> Modified: head/sys/compat/linuxkpi/common/include/linux/file.h >> ============================================================================== >> --- head/sys/compat/linuxkpi/common/include/linux/file.h Mon Nov 30 09:13:04 2015 (r291480) >> +++ head/sys/compat/linuxkpi/common/include/linux/file.h Mon Nov 30 09:24:12 2015 (r291481) >> @@ -2,7 +2,7 @@ >> * Copyright (c) 2010 Isilon Systems, Inc. >> * Copyright (c) 2010 iX Systems, Inc. >> * Copyright (c) 2010 Panasas, Inc. >> - * Copyright (c) 2013 Mellanox Technologies, Ltd. >> + * Copyright (c) 2013-2015 Mellanox Technologies, Ltd. >> * All rights reserved. >> * >> * Redistribution and use in source and binary forms, with or without >> @@ -125,6 +125,21 @@ get_unused_fd(void) >> return fd; >> } >> >> +static inline int >> +get_unused_fd_flags(int flags) >> +{ >> + struct file *file; >> + int error; >> + int fd; >> + >> + error = falloc(curthread, &file, &fd, flags); >> + if (error) >> + return -error; >> + /* drop the extra reference */ >> + fdrop(file, curthread); >> + return fd; >> +} >> + > > This does not look right. > > AFAIR Linux drivers are not going to install fds into kernel threads. So > this would be used for a userspace thread, but then it would completely > insecure. > > Linux model is to reserve a slot in the fd table, obtain a 'file' object > and install it as the last step. > > FreeBSD installs the file right away, but this means an extra reference > has to be held in case something else using the table closes the fd. > > As such, this fdrop can lead to a use-after-free as the file can be > freed from this poin. > > I'm afraid there is no way around patching improted consumers. > Hi Mateusz, Thanks for your input. Yes, there is a potential race there, but no use-after-free from what I can see, because the LinuxKPI always retrieve the file pointer by the file number using "fget_unlocked()". I'll look into if we can delay the fdrop() until after the fd_install(). --HPS
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