Re: [PATCH v13] posix: Deprecate group_member for Linux

[Joe Simmons-Talbott <josimmon@redhat.com>]

On Wed, Apr 10, 2024 at 03:59:06PM -0400, Joe Simmons-Talbott wrote:
> Ping

Ping

Thanks,
Joe
> 
> On Thu, Mar 28, 2024 at 2:07 PM Joe Simmons-Talbott <josimmon@redhat.com> wrote:
> >
> > The alloca usage in group_member could lead to stack overflow on Linux.
> > Removing the alloca usage would require group_member to handle the error
> > condition where memory could not be allocated and that cannot be done
> > since group_member returns a boolean value.  Thus deprecate group_member.
> > Add an internal only implementation of __group_member2 using a
> > scratch_buffer and return -1 for memory allocation errors.  Use
> > __group_member2 in place of __group_member internally.  Add testcases
> > for both group_member and __group_member2.
> > ---
> > Changes to v12:
> > * Rework euidaccess to only call __group_member2 if the euid and egid do
> >   not match.  Use is_group_member rather than gm for the temporary
> >   variable name in both euidaccess and faccessat.
> >
> > Changes to v11:
> > * Rework faccessat as suggested by Paul Eggert to avoid duplicate checks
> >   of EACCESS.
> >
> > Changes to v10:
> > * Only call __group_member2 in faccessat if we didn't match the egid or
> >   gid.
> > * Update copyright year for newly added files to 2024
> >
> > Changes to v9:
> > * v8 didn't actually include the changes due to a missing 'git add'.
> >   Include those changes.
> >
> > Changes to v8:
> > * Remove duplicate calls to __getegid () and __getgid () and convert
> >   nested ternary operators into if/else.
> >
> > Changes to v7:
> > * rebased to latest master.
> >
> > Changes to v6:
> > * Use the intial scratch_buffer size as the starting point for
> >   determining how much space is needed to store the group list.
> > * Call getgroups() with a zero size and set the scratch_buffer size
> >   based on the returned number of groups.
> >
> > Changes to v5:
> > * Add __group_member2 and use it internally in the place of the now
> >   deprecated group_member.
> > * Add a testcase for __group_member2.
> >
> > Changes to v4:
> > * Rebase onto latest commit.
> >
> > Changes to v3:
> > * Fix include guards to match file location _BITS_GROUP_MEMBER_H
> > * Fix indentation of preprocessor directives
> >
> > Changes to v2:
> > * Move the linux group_member.h to the bits directory
> > * Include the correct group_member.h in posix/unistd.h
> >
> > Changes to v1:
> > * Add NEWS entry
> > * Move group_member.h to bits/group_member.h
> > * Include bits/group_member.h in installed headers
> > * Add tests to group_member.h files to only be included from unistd.h
> >
> >  NEWS                                        |  4 ++
> >  bits/group_member.h                         | 31 +++++++++++++++
> >  include/unistd.h                            |  1 +
> >  posix/Makefile                              |  8 ++++
> >  posix/group_member.c                        | 35 +++++++++++++++++
> >  posix/tst-group_member.c                    | 41 ++++++++++++++++++++
> >  posix/tst-group_member2.c                   | 43 +++++++++++++++++++++
> >  posix/unistd.h                              |  6 +--
> >  sysdeps/posix/euidaccess.c                  | 24 ++++++++----
> >  sysdeps/unix/sysv/linux/bits/group_member.h | 32 +++++++++++++++
> >  sysdeps/unix/sysv/linux/faccessat.c         | 27 ++++++++-----
> >  11 files changed, 233 insertions(+), 19 deletions(-)
> >  create mode 100644 bits/group_member.h
> >  create mode 100644 posix/tst-group_member.c
> >  create mode 100644 posix/tst-group_member2.c
> >  create mode 100644 sysdeps/unix/sysv/linux/bits/group_member.h
> >
> > diff --git a/NEWS b/NEWS
> > index da4b2223e9..82e1c43306 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -141,6 +141,10 @@ Deprecated and removed features, and other changes affecting compatibility:
> >
> >  * The ia64*-*-linux-gnu configurations are no longer supported.
> >
> > +* Deprecated group_member on Linux as it uses alloca to allocate a large
> > +  buffer and has no capability for indicating failure for other memory
> > +  allocations.
> > +
> >  Changes to build and runtime requirements:
> >
> >  * Building on LoongArch requires at a minimum binutils 2.41 for vector
> > diff --git a/bits/group_member.h b/bits/group_member.h
> > new file mode 100644
> > index 0000000000..4ec1ef0813
> > --- /dev/null
> > +++ b/bits/group_member.h
> > @@ -0,0 +1,31 @@
> > +/* group_member declaration
> > +   Copyright (C) 2024 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _UNISTD_H
> > +# error "Never use <bits/group_member.h> directly; include <unistd.h> instead."
> > +#endif
> > +
> > +#ifndef _BITS_GROUP_MEMBER_H
> > +# define _BITS_GROUP_MEMBER_H 1
> > +
> > +# ifdef        __USE_GNU
> > +/* Return nonzero iff the calling process is in group GID.  */
> > +extern int group_member (__gid_t __gid) __THROW;
> > +# endif
> > +
> > +#endif /* _BITS_GROUP_MEMBER_H */
> > diff --git a/include/unistd.h b/include/unistd.h
> > index e241603b81..39d5bda372 100644
> > --- a/include/unistd.h
> > +++ b/include/unistd.h
> > @@ -131,6 +131,7 @@ extern __gid_t __getegid (void) attribute_hidden;
> >  extern int __getgroups (int __size, __gid_t __list[]) attribute_hidden;
> >  libc_hidden_proto (__getpgid)
> >  extern int __group_member (__gid_t __gid) attribute_hidden;
> > +extern int __group_member2 (__gid_t __gid) attribute_hidden;
> >  extern int __setuid (__uid_t __uid);
> >  extern int __setreuid (__uid_t __ruid, __uid_t __euid);
> >  extern int __setgid (__gid_t __gid);
> > diff --git a/posix/Makefile b/posix/Makefile
> > index a1e84853a8..b71d6c8750 100644
> > --- a/posix/Makefile
> > +++ b/posix/Makefile
> > @@ -29,6 +29,7 @@ headers := \
> >    bits/getopt_core.h \
> >    bits/getopt_ext.h \
> >    bits/getopt_posix.h \
> > +  bits/group_member.h \
> >    bits/local_lim.h \
> >    bits/mman_ext.h \
> >    bits/posix1_lim.h \
> > @@ -291,6 +292,7 @@ tests := \
> >    tst-glob_symlinks \
> >    tst-gnuglob \
> >    tst-gnuglob64 \
> > +  tst-group_member \
> >    tst-mmap \
> >    tst-mmap-offset \
> >    tst-nanosleep \
> > @@ -479,6 +481,10 @@ tests-special += \
> >    # tests-special
> >  endif
> >
> > +# This test calls __group_member2 directly, which is not exported from glibc.
> > +tests-internal += tst-group_member2
> > +tests-static += tst-group_member2
> > +
> >  include ../Rules
> >
> >  ifeq ($(run-built-tests),yes)
> > @@ -606,6 +612,8 @@ bug-glob1-ARGS = "$(objpfx)"
> >  tst-execvp3-ARGS = --test-dir=$(objpfx)
> >  CFLAGS-tst-spawn3.c += -DOBJPFX=\"$(objpfx)\"
> >
> > +CFLAGS-tst-group_member.c += -Wno-error=deprecated-declarations
> > +
> >  # Test voluntarily overflows struct dirent
> >  CFLAGS-bug-glob2.c += $(no-fortify-source)
> >
> > diff --git a/posix/group_member.c b/posix/group_member.c
> > index 9d68f57a68..bb92f4d631 100644
> > --- a/posix/group_member.c
> > +++ b/posix/group_member.c
> > @@ -18,6 +18,7 @@
> >
> >  #include <sys/types.h>
> >  #include <unistd.h>
> > +#include <scratch_buffer.h>
> >  #include <stdlib.h>
> >  #include <limits.h>
> >
> > @@ -47,3 +48,37 @@ __group_member (gid_t gid)
> >    return 0;
> >  }
> >  weak_alias (__group_member, group_member)
> > +
> > +int
> > +__group_member2 (gid_t gid)
> > +{
> > +  int n;
> > +  gid_t *groups;
> > +  struct scratch_buffer sbuf;
> > +  scratch_buffer_init (&sbuf);
> > +  groups = sbuf.data;
> > +
> > +  do
> > +    {
> > +      n = __getgroups (0, NULL);
> > +      if (n > sbuf.length)
> > +       {
> > +         if (!scratch_buffer_set_array_size (&sbuf, sizeof (*groups), n))
> > +           return -1;
> > +         groups = sbuf.data;
> > +       }
> > +
> > +      n = __getgroups (n, groups);
> > +    }
> > +  while (n > sbuf.length);
> > +
> > +  while (n-- > 0)
> > +    if (groups[n] == gid)
> > +      {
> > +       scratch_buffer_free (&sbuf);
> > +        return 1;
> > +      }
> > +
> > +  scratch_buffer_free (&sbuf);
> > +  return 0;
> > +}
> > diff --git a/posix/tst-group_member.c b/posix/tst-group_member.c
> > new file mode 100644
> > index 0000000000..cc7f91618e
> > --- /dev/null
> > +++ b/posix/tst-group_member.c
> > @@ -0,0 +1,41 @@
> > +/* Basic tests for group_member.
> > +   Copyright (C) 2024 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#include <alloca.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <unistd.h>
> > +
> > +#include <support/check.h>
> > +
> > +static int do_test (void)
> > +{
> > +  int n;
> > +  gid_t *groups;
> > +
> > +  n = getgroups (0, NULL);
> > +  groups = alloca (n * sizeof (*groups));
> > +  n = getgroups (n, groups);
> > +
> > +  while (n-- > 0)
> > +    TEST_COMPARE (1, group_member(groups[n]));
> > +
> > +  return EXIT_SUCCESS;
> > +}
> > +
> > +#include <support/test-driver.c>
> > diff --git a/posix/tst-group_member2.c b/posix/tst-group_member2.c
> > new file mode 100644
> > index 0000000000..8f86d5a1e9
> > --- /dev/null
> > +++ b/posix/tst-group_member2.c
> > @@ -0,0 +1,43 @@
> > +/* Basic tests for group_member.
> > +   Copyright (C) 2024 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#include <alloca.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <posix/unistd.h>
> > +
> > +#include <support/check.h>
> > +
> > +extern int __group_member2 (__gid_t __gid);
> > +
> > +static int do_test (void)
> > +{
> > +  int n;
> > +  gid_t *groups;
> > +
> > +  n = getgroups (0, NULL);
> > +  groups = alloca (n * sizeof (*groups));
> > +  n = getgroups (n, groups);
> > +
> > +  while (n-- > 0)
> > +    TEST_COMPARE (1, __group_member2(groups[n]));
> > +
> > +  return EXIT_SUCCESS;
> > +}
> > +
> > +#include <support/test-driver.c>
> > diff --git a/posix/unistd.h b/posix/unistd.h
> > index 54d7d7527e..411de1d6d4 100644
> > --- a/posix/unistd.h
> > +++ b/posix/unistd.h
> > @@ -710,10 +710,10 @@ extern __gid_t getegid (void) __THROW;
> >     of its supplementary groups in LIST and return the number written.  */
> >  extern int getgroups (int __size, __gid_t __list[]) __THROW __wur
> >      __fortified_attr_access (__write_only__, 2, 1);
> > +
> >  #ifdef __USE_GNU
> > -/* Return nonzero iff the calling process is in group GID.  */
> > -extern int group_member (__gid_t __gid) __THROW;
> > -#endif
> > +# include <bits/group_member.h>
> > +#endif
> >
> >  /* Set the user ID of the calling process to UID.
> >     If the calling process is the super-user, set the real
> > diff --git a/sysdeps/posix/euidaccess.c b/sysdeps/posix/euidaccess.c
> > index 4c5c2220bd..da185dec3e 100644
> > --- a/sysdeps/posix/euidaccess.c
> > +++ b/sysdeps/posix/euidaccess.c
> > @@ -81,7 +81,7 @@ extern int errno;
> >
> >  #ifdef _LIBC
> >
> > -# define group_member __group_member
> > +# define group_member __group_member2
> >  # define euidaccess __euidaccess
> >
> >  #else
> > @@ -120,7 +120,6 @@ int
> >  euidaccess (const char *path, int mode)
> >  {
> >    struct __stat64_t64 stats;
> > -  int granted;
> >
> >  #ifdef _LIBC
> >    uid_t euid;
> > @@ -167,15 +166,26 @@ euidaccess (const char *path, int mode)
> >                     || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
> >      return 0;
> >
> > +  int shift;
> > +
> >    if (euid == stats.st_uid)
> > -    granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
> > -  else if (egid == stats.st_gid || group_member (stats.st_gid))
> > -    granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
> > +    shift = 6;
> >    else
> > -    granted = (stats.st_mode & mode);
> > +    {
> > +      int is_group_member = (egid == stats.st_gid);
> > +      if (!is_group_member)
> > +        {
> > +          is_group_member = group_member (stats.st_gid);
> > +          if (is_group_member < 0)
> > +            return is_group_member;
> > +       }
> > +      shift = is_group_member ? 3 : 0;
> > +    }
> > +
> >    /* XXX Add support for ACLs.  */
> > -  if (granted == mode)
> > +  if ((stats.st_mode >> shift & mode) == mode)
> >      return 0;
> > +
> >    __set_errno (EACCESS);
> >    return -1;
> >  }
> > diff --git a/sysdeps/unix/sysv/linux/bits/group_member.h b/sysdeps/unix/sysv/linux/bits/group_member.h
> > new file mode 100644
> > index 0000000000..ad77e65f9b
> > --- /dev/null
> > +++ b/sysdeps/unix/sysv/linux/bits/group_member.h
> > @@ -0,0 +1,32 @@
> > +/* group_member declaration
> > +   Copyright (C) 2024 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> > +
> > +   The GNU C Library is free software; you can redistribute it and/or
> > +   modify it under the terms of the GNU Lesser General Public
> > +   License as published by the Free Software Foundation; either
> > +   version 2.1 of the License, or (at your option) any later version.
> > +
> > +   The GNU C Library is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > +   Lesser General Public License for more details.
> > +
> > +   You should have received a copy of the GNU Lesser General Public
> > +   License along with the GNU C Library; if not, see
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef _UNISTD_H
> > +# error "Never use <bits/group_member.h> directly; include <unistd.h> instead."
> > +#endif
> > +
> > +#ifndef _BITS_GROUP_MEMBER_H
> > +# define _BITS_GROUP_MEMBER_H 1
> > +
> > +# ifdef        __USE_GNU
> > +/* Return nonzero iff the calling process is in group GID.  Deprecated */
> > +extern int group_member (__gid_t __gid) __THROW
> > +       __attribute_deprecated_msg__ ("may overflow the stack");
> > +# endif
> > +
> > +#endif /* _BITS_GROUP_MEMBER_H */
> > diff --git a/sysdeps/unix/sysv/linux/faccessat.c b/sysdeps/unix/sysv/linux/faccessat.c
> > index 2fa57fd63d..03232103b4 100644
> > --- a/sysdeps/unix/sysv/linux/faccessat.c
> > +++ b/sysdeps/unix/sysv/linux/faccessat.c
> > @@ -59,15 +59,24 @@ __faccessat (int fd, const char *file, int mode, int flag)
> >                    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
> >      return 0;
> >
> > -  int granted = (uid == stats.st_uid
> > -                ? (unsigned int) (stats.st_mode & (mode << 6)) >> 6
> > -                : (stats.st_gid == ((flag & AT_EACCESS)
> > -                                    ? __getegid () : __getgid ())
> > -                   || __group_member (stats.st_gid))
> > -                ? (unsigned int) (stats.st_mode & (mode << 3)) >> 3
> > -                : (stats.st_mode & mode));
> > -
> > -  if (granted == mode)
> > +  int shift;
> > +
> > +  if (uid == stats.st_uid)
> > +    shift = 6;
> > +  else
> > +    {
> > +      int is_group_member = (stats.st_gid
> > +                == (flag & AT_EACCESS ? __getegid () : __getgid ()));
> > +      if (!is_group_member)
> > +        {
> > +          is_group_member = __group_member2 (stats.st_gid);
> > +          if (is_group_member < 0)
> > +            return is_group_member;
> > +        }
> > +      shift = is_group_member ? 3 : 0;
> > +    }
> > +
> > +  if ((stats.st_mode >> shift & mode) == mode)
> >      return 0;
> >
> >    return INLINE_SYSCALL_ERROR_RETURN_VALUE (EACCES);
> > --
> > 2.44.0
> >
> 
> 
> -- 
> Joe Simmons-Talbott