[OE-core] [PATCH][RFC] pseudo: intercept syscall() and return ENOTSUP for renameat2

[Andre McCurdy]

On Tue, Mar 27, 2018 at 8:48 AM, Ross Burton <ross.burton at intel.com> wrote:
> coreutils is now using renameat2() in mv(1) but as this syscall isn't in most
> glibc headers yet it falls back to directly calling syscall(), which pseudo
> doesn't intercept.  This results in permission problems as files mysteriously
> move without pseudo knowing.
>
> This patch intercepts syscall() and returns ENOTSUP if renameat2() is being
> called.  Thanks to Andre McCurdy for the proof-of-concept that this patch is
> based on.

Tested-by: Andre McCurdy <armccurdy at gmail.com>

> Signed-off-by: Ross Burton <ross.burton at intel.com>
> ---
>  meta/recipes-devtools/pseudo/files/renameat2.patch | 63 ++++++++++++++++++++++
>  meta/recipes-devtools/pseudo/pseudo_git.bb         |  1 +
>  2 files changed, 64 insertions(+)
>  create mode 100644 meta/recipes-devtools/pseudo/files/renameat2.patch
>
> diff --git a/meta/recipes-devtools/pseudo/files/renameat2.patch b/meta/recipes-devtools/pseudo/files/renameat2.patch
> new file mode 100644
> index 00000000000..467b0b3e79f
> --- /dev/null
> +++ b/meta/recipes-devtools/pseudo/files/renameat2.patch
> @@ -0,0 +1,63 @@
> +commit 3a4c536817dce4d0cbaa8f4efe30e722108357dd
> +Author: Ross Burton <ross.burton at intel.com>
> +Date:   Tue Mar 27 14:02:10 2018 +0100
> +
> +    HACK syscall
> +
> +diff --git a/ports/linux/guts/syscall.c b/ports/linux/guts/syscall.c
> +new file mode 100644
> +index 0000000..4ed38ed
> +--- /dev/null
> ++++ b/ports/linux/guts/syscall.c
> +@@ -0,0 +1,30 @@
> ++/*
> ++ * Copyright (c) 2018 Wind River Systems; see
> ++ * guts/COPYRIGHT for information.
> ++ *
> ++ * long syscall(long number, ...)
> ++ *    long rc = -1;
> ++ */
> ++      typedef long syscall_arg_t;
> ++      syscall_arg_t a,b,c,d,e,f;
> ++
> ++      //va_start (ap, number);

Without knowing anything about pseudo, commenting this out looks odd?

> ++      a = va_arg (ap, syscall_arg_t);
> ++      b = va_arg (ap, syscall_arg_t);
> ++      c = va_arg (ap, syscall_arg_t);
> ++      d = va_arg (ap, syscall_arg_t);
> ++      e = va_arg (ap, syscall_arg_t);
> ++      f = va_arg (ap, syscall_arg_t);
> ++      va_end (ap);
> ++
> ++      if ((number == SYS_renameat2)) {
> ++                      errno = ENOTSUP;

I think ENOTSUP is intended to indicate that the failing syscall may
succeed in another context (e.g. fails on a file but may succeed on a
socket, etc ?).

In this case, it may be better to return ENOSYS, which indicates the
syscall is never expected to work on this system. It's the error
returned by a kernel which is too old to support renameat2 and so
anything trying to use renameat2 is likely to check for it.

gnulib checks for both though, so either is going to work for the
current problem with coreutils mv.

> ++                      rc = -1;
> ++      }
> ++      else {
> ++                      rc = real_syscall (number, a, b, c, d, e, f);
> ++      }
> ++
> ++/*    return rc;
> ++ * }
> ++ */
> +diff --git a/ports/linux/wrapfuncs.in b/ports/linux/wrapfuncs.in
> +index fca5b50..137612c 100644
> +--- a/ports/linux/wrapfuncs.in
> ++++ b/ports/linux/wrapfuncs.in
> +@@ -54,3 +54,4 @@ int getpw(uid_t uid, char *buf);
> + int getpwent_r(struct passwd *pwbuf, char *buf, size_t buflen, struct passwd **pwbufp);
> + int getgrent_r(struct group *gbuf, char *buf, size_t buflen, struct group **gbufp);
> + int capset(cap_user_header_t hdrp, const cap_user_data_t datap); /* real_func=pseudo_capset */
> ++long syscall(long number, ...);
> +diff --git a/pseudo_wrappers.c b/pseudo_wrappers.c
> +index e05f73a..b7225d7 100644
> +--- a/pseudo_wrappers.c
> ++++ b/pseudo_wrappers.c
> +@@ -36,6 +36,7 @@
> + #include <sys/time.h>
> + #include <sys/wait.h>
> + #include <dlfcn.h>
> ++#include <sys/syscall.h>
> +
> + /* include this to get PSEUDO_PORT_* definitions */
> + #include "pseudo.h"
> diff --git a/meta/recipes-devtools/pseudo/pseudo_git.bb b/meta/recipes-devtools/pseudo/pseudo_git.bb
> index 66da1cc53b8..44343c3bc57 100644
> --- a/meta/recipes-devtools/pseudo/pseudo_git.bb
> +++ b/meta/recipes-devtools/pseudo/pseudo_git.bb
> @@ -6,6 +6,7 @@ SRC_URI = "git://git.yoctoproject.org/pseudo \
>             file://fallback-group \
>             file://moreretries.patch \
>             file://toomanyfiles.patch \
> +           file://renameat2.patch \
>             "
>
>  SRCREV = "d7c31a25e4b02af0c64e6be0b4b0a9ac4ffc9da2"
> --
> 2.11.0
>
> --
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