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From: Petr Lautrbach <plautrba@redhat.com>
To: SElinux list <selinux@vger.kernel.org>
Cc: Smalley <stephen.smalley.work@gmail.com>,
	Nicolas Iooss <nicolas.iooss@m4x.org>
Subject: Re: [PATCH v2] libsemanage: fsync final files before rename
Date: Fri, 15 May 2020 15:42:17 +0200	[thread overview]
Message-ID: <20200515134217.GF255621@workstation> (raw)
In-Reply-To: <CAJfZ7==4oSmvECxX-Roarvc5w=EsAtF=M-yjGv2bQD9rN7GUeg@mail.gmail.com>

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On Thu, May 14, 2020 at 08:44:42PM +0200, Nicolas Iooss wrote:
> On Wed, May 13, 2020 at 9:34 PM Smalley <stephen.smalley.work@gmail.com> wrote:
> >
> > From: Stephen Smalley <stephen.smalley.work@gmail.com>
> >
> > Prior to rename(2)'ing the final selinux policy files into place,
> > fsync(2) them to ensure the contents will be fully written prior to
> > rename.  While we are here, also fix checking of write(2) to detect
> > short writes and treat them as an error.  This code could be more
> > generally improved but keeping to the minimal changes required to fix
> > this bug.
> >
> > Fixes: https://github.com/SELinuxProject/selinux/issues/237
> > Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
> > ---
> > v2 falls back to EIO if errno is not set by a short write, and
> > only fsync's the final selinux policy files being created in
> > /etc/selinux, avoiding the overhead of fsync on every file copied
> > under /var/lib/selinux.
> >
> >  libsemanage/src/direct_api.c     | 10 +++++-----
> >  libsemanage/src/semanage_store.c | 20 +++++++++++++++-----
> >  libsemanage/src/semanage_store.h |  4 +++-
> >  3 files changed, 23 insertions(+), 11 deletions(-)
> >
> > diff --git a/libsemanage/src/direct_api.c b/libsemanage/src/direct_api.c
> > index 1088a0ac..d2b91fb2 100644
> > --- a/libsemanage/src/direct_api.c
> > +++ b/libsemanage/src/direct_api.c
> > @@ -1188,7 +1188,7 @@ cleanup:
> >   * overwrite it. If source doesn't exist then return success.
> >   * Returns 0 on success, -1 on error. */
> >  static int copy_file_if_exists(const char *src, const char *dst, mode_t mode){
> > -       int rc = semanage_copy_file(src, dst, mode);
> > +       int rc = semanage_copy_file(src, dst, mode, false);
> >         return (rc < 0 && errno != ENOENT) ? rc : 0;
> >  }
> >
> > @@ -1488,7 +1488,7 @@ rebuild:
> >                         retval = semanage_copy_file(path,
> >                                                     semanage_path(SEMANAGE_TMP,
> >                                                                   SEMANAGE_STORE_SEUSERS),
> > -                                                   0);
> > +                                                   0, false);
> >                         if (retval < 0)
> >                                 goto cleanup;
> >                         pseusers->dtable->drop_cache(pseusers->dbase);
> > @@ -1506,7 +1506,7 @@ rebuild:
> >                         retval = semanage_copy_file(path,
> >                                                     semanage_path(SEMANAGE_TMP,
> >                                                                   SEMANAGE_USERS_EXTRA),
> > -                                                   0);
> > +                                                   0, false);
> >                         if (retval < 0)
> >                                 goto cleanup;
> >                         pusers_extra->dtable->drop_cache(pusers_extra->dbase);
> > @@ -1595,7 +1595,7 @@ rebuild:
> >
> >         retval = semanage_copy_file(semanage_path(SEMANAGE_TMP, SEMANAGE_STORE_KERNEL),
> >                         semanage_final_path(SEMANAGE_FINAL_TMP, SEMANAGE_KERNEL),
> > -                       sh->conf->file_mode);
> > +                       sh->conf->file_mode, false);
> >         if (retval < 0) {
> >                 goto cleanup;
> >         }
> > @@ -1634,7 +1634,7 @@ rebuild:
> >                         retval = semanage_copy_file(
> >                                                 semanage_path(SEMANAGE_TMP, SEMANAGE_STORE_FC_HOMEDIRS),
> >                                                 semanage_final_path(SEMANAGE_FINAL_TMP, SEMANAGE_FC_HOMEDIRS),
> > -                                               sh->conf->file_mode);
> > +                                               sh->conf->file_mode, false);
> >                         if (retval < 0) {
> >                                 goto cleanup;
> >                         }
> > diff --git a/libsemanage/src/semanage_store.c b/libsemanage/src/semanage_store.c
> > index 859c0a22..cd5e46bb 100644
> > --- a/libsemanage/src/semanage_store.c
> > +++ b/libsemanage/src/semanage_store.c
> > @@ -707,7 +707,8 @@ static int semanage_filename_select(const struct dirent *d)
> >
> >  /* Copies a file from src to dst.  If dst already exists then
> >   * overwrite it.  Returns 0 on success, -1 on error. */
> > -int semanage_copy_file(const char *src, const char *dst, mode_t mode)
> > +int semanage_copy_file(const char *src, const char *dst, mode_t mode,
> > +               bool syncrequired)
> >  {
> >         int in, out, retval = 0, amount_read, n, errsv = errno;
> >         char tmp[PATH_MAX];
> > @@ -735,8 +736,11 @@ int semanage_copy_file(const char *src, const char *dst, mode_t mode)
> >         }
> >         umask(mask);
> >         while (retval == 0 && (amount_read = read(in, buf, sizeof(buf))) > 0) {
> > -               if (write(out, buf, amount_read) < 0) {
> > -                       errsv = errno;
> > +               if (write(out, buf, amount_read) != amount_read) {
> > +                       if (errno)
> > +                               errsv = errno;
> > +                       else
> > +                               errsv = EIO;
> >                         retval = -1;
> >                 }
> >         }
> > @@ -745,6 +749,10 @@ int semanage_copy_file(const char *src, const char *dst, mode_t mode)
> >                 retval = -1;
> >         }
> >         close(in);
> > +       if (syncrequired && fsync(out) < 0) {
> > +               errsv = errno;
> > +               retval = -1;
> > +       }
> 
> The patch looks good to me, even though I am wondering whether it
> makes sense to call fsync() if an error happens (by changing the
> condition to "if (!retval && syncrequired && fsync(out) < 0)").
> Anyway, this is a minor comment and I am fine with the other changes.
> 
> Acked-by: Nicolas Iooss <nicolas.iooss@m4x.org>
> 

Applied.


> >         if (close(out) < 0) {
> >                 errsv = errno;
> >                 retval = -1;
> > @@ -811,7 +819,8 @@ static int semanage_copy_dir_flags(const char *src, const char *dst, int flag)
> >                         umask(mask);
> >                 } else if (S_ISREG(sb.st_mode) && flag == 1) {
> >                         mask = umask(0077);
> > -                       if (semanage_copy_file(path, path2, sb.st_mode) < 0) {
> > +                       if (semanage_copy_file(path, path2, sb.st_mode,
> > +                                               false) < 0) {
> >                                 umask(mask);
> >                                 goto cleanup;
> >                         }
> > @@ -1639,7 +1648,8 @@ static int semanage_install_final_tmp(semanage_handle_t * sh)
> >                         goto cleanup;
> >                 }
> >
> > -               ret = semanage_copy_file(src, dst, sh->conf->file_mode);
> > +               ret = semanage_copy_file(src, dst, sh->conf->file_mode,
> > +                                       true);
> >                 if (ret < 0) {
> >                         ERR(sh, "Could not copy %s to %s.", src, dst);
> >                         goto cleanup;
> > diff --git a/libsemanage/src/semanage_store.h b/libsemanage/src/semanage_store.h
> > index 34bf8523..b9ec5664 100644
> > --- a/libsemanage/src/semanage_store.h
> > +++ b/libsemanage/src/semanage_store.h
> > @@ -24,6 +24,7 @@
> >  #ifndef SEMANAGE_MODULE_STORE_H
> >  #define SEMANAGE_MODULE_STORE_H
> >
> > +#include <stdbool.h>
> >  #include <sys/time.h>
> >  #include <sepol/module.h>
> >  #include <sepol/cil/cil.h>
> > @@ -162,6 +163,7 @@ int semanage_nc_sort(semanage_handle_t * sh,
> >                      size_t buf_len,
> >                      char **sorted_buf, size_t * sorted_buf_len);
> >
> > -int semanage_copy_file(const char *src, const char *dst, mode_t mode);
> > +int semanage_copy_file(const char *src, const char *dst, mode_t mode,
> > +               bool syncrequired);
> >
> >  #endif
> > --
> > 2.23.3
> >
> 

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      reply	other threads:[~2020-05-15 13:42 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13 19:34 Smalley
2020-05-14 18:44 ` Nicolas Iooss
2020-05-15 13:42   ` Petr Lautrbach [this message]

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