1. 25 Feb, 2020 1 commit
    • Paul Burton's avatar
      MAINTAINERS: Hand MIPS over to Thomas · 3234f4ed
      Paul Burton authored
      My time with MIPS the company has reached its end, and so at best I'll
      have little time spend on maintaining arch/mips/.
      
      Ralf last authored a patch over 2 years ago, the last time he committed
      one is even further back & activity was sporadic for a while before
      that. The reality is that he isn't active.
      
      Having a new maintainer with time to do things properly will be
      beneficial all round. Thomas Bogendoerfer has been involved in MIPS
      development for a long time & has offered to step up as maintainer, so
      add Thomas and remove myself & Ralf from the MIPS entry.
      
      Ralf already has an entry in CREDITS to honor his contributions, so this
      just adds one for me.
      Signed-off-by: default avatarPaul Burton <paulburton@kernel.org>
      Reviewed-by: default avatarPhilippe Mathieu-Daudé <f4bug@amsat.org>
      Acked-by: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
      Cc: Ralf Baechle <ralf@linux-mips.org>
      Cc: linux-kernel@vger.kernel.org
      Cc: linux-mips@vger.kernel.org
      3234f4ed
  2. 18 Jan, 2020 1 commit
    • Aleksa Sarai's avatar
      open: introduce openat2(2) syscall · fddb5d43
      Aleksa Sarai authored
      /* Background. */
      For a very long time, extending openat(2) with new features has been
      incredibly frustrating. This stems from the fact that openat(2) is
      possibly the most famous counter-example to the mantra "don't silently
      accept garbage from userspace" -- it doesn't check whether unknown flags
      are present[1].
      
      This means that (generally) the addition of new flags to openat(2) has
      been fraught with backwards-compatibility issues (O_TMPFILE has to be
      defined as __O_TMPFILE|O_DIRECTORY|[O_RDWR or O_WRONLY] to ensure old
      kernels gave errors, since it's insecure to silently ignore the
      flag[2]). All new security-related flags therefore have a tough road to
      being added to openat(2).
      
      Userspace also has a hard time figuring out whether a particular flag is
      supported on a particular kernel. While it is now possible with
      contemporary kernels (thanks to [3]), older kernels will expose unknown
      flag bits through fcntl(F_GETFL). Giving a clear -EINVAL during
      openat(2) time matches modern syscall designs and is far more
      fool-proof.
      
      In addition, the newly-added path resolution restriction LOOKUP flags
      (which we would like to expose to user-space) don't feel related to the
      pre-existing O_* flag set -- they affect all components of path lookup.
      We'd therefore like to add a new flag argument.
      
      Adding a new syscall allows us to finally fix the flag-ignoring problem,
      and we can make it extensible enough so that we will hopefully never
      need an openat3(2).
      
      /* Syscall Prototype. */
        /*
         * open_how is an extensible structure (similar in interface to
         * clone3(2) or sched_setattr(2)). The size parameter must be set to
         * sizeof(struct open_how), to allow for future extensions. All future
         * extensions will be appended to open_how, with their zero value
         * acting as a no-op default.
         */
        struct open_how { /* ... */ };
      
        int openat2(int dfd, const char *pathname,
                    struct open_how *how, size_t size);
      
      /* Description. */
      The initial version of 'struct open_how' contains the following fields:
      
        flags
          Used to specify openat(2)-style flags. However, any unknown flag
          bits or otherwise incorrect flag combinations (like O_PATH|O_RDWR)
          will result in -EINVAL. In addition, this field is 64-bits wide to
          allow for more O_ flags than currently permitted with openat(2).
      
        mode
          The file mode for O_CREAT or O_TMPFILE.
      
          Must be set to zero if flags does not contain O_CREAT or O_TMPFILE.
      
        resolve
          Restrict path resolution (in contrast to O_* flags they affect all
          path components). The current set of flags are as follows (at the
          moment, all of the RESOLVE_ flags are implemented as just passing
          the corresponding LOOKUP_ flag).
      
          RESOLVE_NO_XDEV       => LOOKUP_NO_XDEV
          RESOLVE_NO_SYMLINKS   => LOOKUP_NO_SYMLINKS
          RESOLVE_NO_MAGICLINKS => LOOKUP_NO_MAGICLINKS
          RESOLVE_BENEATH       => LOOKUP_BENEATH
          RESOLVE_IN_ROOT       => LOOKUP_IN_ROOT
      
      open_how does not contain an embedded size field, because it is of
      little benefit (userspace can figure out the kernel open_how size at
      runtime fairly easily without it). It also only contains u64s (even
      though ->mode arguably should be a u16) to avoid having padding fields
      which are never used in the future.
      
      Note that as a result of the new how->flags handling, O_PATH|O_TMPFILE
      is no longer permitted for openat(2). As far as I can tell, this has
      always been a bug and appears to not be used by userspace (and I've not
      seen any problems on my machines by disallowing it). If it turns out
      this breaks something, we can special-case it and only permit it for
      openat(2) but not openat2(2).
      
      After input from Florian Weimer, the new open_how and flag definitions
      are inside a separate header from uapi/linux/fcntl.h, to avoid problems
      that glibc has with importing that header.
      
      /* Testing. */
      In a follow-up patch there are over 200 selftests which ensure that this
      syscall has the correct semantics and will correctly handle several
      attack scenarios.
      
      In addition, I've written a userspace library[4] which provides
      convenient wrappers around openat2(RESOLVE_IN_ROOT) (this is necessary
      because no other syscalls support RESOLVE_IN_ROOT, and thus lots of care
      must be taken when using RESOLVE_IN_ROOT'd file descriptors with other
      syscalls). During the development of this patch, I've run numerous
      verification tests using libpathrs (showing that the API is reasonably
      usable by userspace).
      
      /* Future Work. */
      Additional RESOLVE_ flags have been suggested during the review period.
      These can be easily implemented separately (such as blocking auto-mount
      during resolution).
      
      Furthermore, there are some other proposed changes to the openat(2)
      interface (the most obvious example is magic-link hardening[5]) which
      would be a good opportunity to add a way for userspace to restrict how
      O_PATH file descriptors can be re-opened.
      
      Another possible avenue of future work would be some kind of
      CHECK_FIELDS[6] flag which causes the kernel to indicate to userspace
      which openat2(2) flags and fields are supported by the current kernel
      (to avoid userspace having to go through several guesses to figure it
      out).
      
      [1]: https://lwn.net/Articles/588444/
      [2]: https://lore.kernel.org/lkml/CA+55aFyyxJL1LyXZeBsf2ypriraj5ut1XkNDsunRBqgVjZU_6Q@mail.gmail.com
      [3]: commit 629e014b ("fs: completely ignore unknown open flags")
      [4]: https://sourceware.org/bugzilla/show_bug.cgi?id=17523
      [5]: https://lore.kernel.org/lkml/20190930183316.10190-2-cyphar@cyphar.com/
      [6]: https://youtu.be/ggD-eb3yPVsSuggested-by: default avatarChristian Brauner <christian.brauner@ubuntu.com>
      Signed-off-by: default avatarAleksa Sarai <cyphar@cyphar.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      fddb5d43
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  34. 29 Mar, 2016 1 commit
    • Linus Walleij's avatar
      Documentation: update the devices.txt documentation · ebdf4040
      Linus Walleij authored
      Alan is no longer maintaining this list through the Linux assigned
      numbers authority. Make it a collective document by referring to
      "the maintainers" in plural throughout, and naming the chardev and
      block layer maintainers in particular as parties of involvement.
      Cut down and remove some sections that pertained to the process of
      maintaining the list at lanana.org and contacting Alan directly.
      
      Make it clear that this document, in the kernel, is the master
      document.
      
      Also move paragraphs around so as to emphasize dynamic major number
      allocation.
      
      Remove paragraph on 2.6 deprecation, that tag no longer appears
      anywhere in the file.
      
      Cc: Jonathan Corbet <corbet@lwn.net>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Alan Cox <alan@linux.intel.com>
      Cc: Arnd Bergmann <arnd@arndb.de>
      Cc: Jens Axboe <axboe@kernel.dk>
      Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      ebdf4040
  35. 24 Jan, 2016 1 commit
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