[PATCH v11] posix: Deprecate group_member for Linux

[PATCH v11] posix: Deprecate group_member for Linux

[Joe Simmons-Talbott]

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 for in place of __group_member internally.  Add testcases
for both group_member and __group_member2.
---
Changes vo 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 vo 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                  |  9 ++++-
 sysdeps/unix/sysv/linux/bits/group_member.h | 32 +++++++++++++++
 sysdeps/unix/sysv/linux/faccessat.c         | 27 +++++++++----
 11 files changed, 225 insertions(+), 12 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..0c19021a30 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
@@ -167,9 +167,14 @@ euidaccess (const char *path, int mode)
 		    || (stats.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))))
     return 0;
 
+  int gm = group_member (stats.st_gid);
+  if (euid != stats.st_uid && egid != stats.st_gid)
+    if (gm == -1)
+      return -1;
+
   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))
+  else if (egid == stats.st_gid || gm)
     granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
   else
     granted = (stats.st_mode & mode);
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..542a363eea 100644
--- a/sysdeps/unix/sysv/linux/faccessat.c
+++ b/sysdeps/unix/sysv/linux/faccessat.c
@@ -59,13 +59,26 @@ __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));
+  int granted;
+
+  if (uid == stats.st_uid)
+    granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
+  else
+    {
+      if (((flag & AT_EACCESS) && stats.st_gid == __getegid()) ||
+          (!(flag & AT_EACCESS) && stats.st_gid == __getgid()))
+        granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
+      else
+        {
+          int gm = __group_member2 (stats.st_gid);
+          if (gm == -1)
+            return -1;
+          else if (gm)
+            granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
+          else
+            granted = (stats.st_mode & mode);
+        }
+    }
 
   if (granted == mode)
     return 0;
-- 
2.44.0

Re: [PATCH v11] posix: Deprecate group_member for Linux

[Paul Eggert]

On 3/27/24 12:43, Joe Simmons-Talbott wrote:
> +  int granted;
> +
> +  if (uid == stats.st_uid)
> +    granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
> +  else
> +    {
> +      if (((flag & AT_EACCESS) && stats.st_gid == __getegid()) ||
> +          (!(flag & AT_EACCESS) && stats.st_gid == __getgid()))
> +        granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
> +      else
> +        {
> +          int gm = __group_member2 (stats.st_gid);
> +          if (gm == -1)
> +            return -1;
> +          else if (gm)
> +            granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
> +          else
> +            granted = (stats.st_mode & mode);
> +        }
> +    }
>   
>     if (granted == mode)
>       return 0;

This is still too complicated, with repetitions of AT_EACCESS that were 
not in the original. Come to think of it, it has unnecessary casts and 
repetitive shifting and masking, and that indentation of || is not GNU 
style. How about something like the following untested code instead?

   int shift;

   if (uid == stats.st_uid)
     shift = 6;
   else
     {
       int gm = (stats.st_gid
		== (flag & AT_EACCESS ? __getegid () : __getgid ()));
       if (!gm)
	{
           gm = __group_member2 (stats.st_gid);
           if (gm < 0)
             return gm;
         }
       shift = gm ? 3 : 0;
     }

   if ((stats.st_mode >> shift & mode) == mode)
     return 0;

Re: [PATCH v11] posix: Deprecate group_member for Linux

[Joe Simmons-Talbott]

On Wed, Mar 27, 2024 at 4:57 PM Paul Eggert <eggert@cs.ucla.edu> wrote:
>
> On 3/27/24 12:43, Joe Simmons-Talbott wrote:
> > +  int granted;
> > +
> > +  if (uid == stats.st_uid)
> > +    granted = (unsigned int) (stats.st_mode & (mode << 6)) >> 6;
> > +  else
> > +    {
> > +      if (((flag & AT_EACCESS) && stats.st_gid == __getegid()) ||
> > +          (!(flag & AT_EACCESS) && stats.st_gid == __getgid()))
> > +        granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
> > +      else
> > +        {
> > +          int gm = __group_member2 (stats.st_gid);
> > +          if (gm == -1)
> > +            return -1;
> > +          else if (gm)
> > +            granted = (unsigned int) (stats.st_mode & (mode << 3)) >> 3;
> > +          else
> > +            granted = (stats.st_mode & mode);
> > +        }
> > +    }
> >
> >     if (granted == mode)
> >       return 0;
>
> This is still too complicated, with repetitions of AT_EACCESS that were
> not in the original. Come to think of it, it has unnecessary casts and
> repetitive shifting and masking, and that indentation of || is not GNU
> style. How about something like the following untested code instead?
>
>    int shift;
>
>    if (uid == stats.st_uid)
>      shift = 6;
>    else
>      {
>        int gm = (stats.st_gid
>                 == (flag & AT_EACCESS ? __getegid () : __getgid ()));
>        if (!gm)
>         {
>            gm = __group_member2 (stats.st_gid);
>            if (gm < 0)
>              return gm;
>          }
>        shift = gm ? 3 : 0;
>      }
>
>    if ((stats.st_mode >> shift & mode) == mode)
>      return 0;
>

I like that much better.  I've posted a v12[1] with your suggestion
that was tested via 'make check'.

Thanks,
Joe

[1] https://sourceware.org/pipermail/libc-alpha/2024-March/155666.html

-- 
Joe Simmons-Talbott