[v3] posix: Deprecate group_member for Linux
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Commit Message
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 a testcase.
---
Changes to v2:
* Move the linux group_member.h to the bits directory
* Include the correct group_member.h in posix/unistd.h
NEWS | 5 ++-
bits/group_member.h | 31 ++++++++++++++++
posix/Makefile | 4 ++
posix/tst-group_member.c | 41 +++++++++++++++++++++
posix/unistd.h | 6 +--
sysdeps/unix/sysv/linux/bits/group_member.h | 32 ++++++++++++++++
6 files changed, 115 insertions(+), 4 deletions(-)
create mode 100644 bits/group_member.h
create mode 100644 posix/tst-group_member.c
create mode 100644 sysdeps/unix/sysv/linux/bits/group_member.h
Comments
On Okt 17 2023, Joe Simmons-Talbott wrote:
> +#ifndef _GROUP_MEMBER_H
> +#define _GROUP_MEMBER_H 1
That should be _BITS_GROUP_MEMBER_H.
* 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 a testcase.
> ---
> Changes to v2:
> * Move the linux group_member.h to the bits directory
> * Include the correct group_member.h in posix/unistd.h
>
> NEWS | 5 ++-
> bits/group_member.h | 31 ++++++++++++++++
> posix/Makefile | 4 ++
> posix/tst-group_member.c | 41 +++++++++++++++++++++
> posix/unistd.h | 6 +--
> sysdeps/unix/sysv/linux/bits/group_member.h | 32 ++++++++++++++++
> 6 files changed, 115 insertions(+), 4 deletions(-)
> create mode 100644 bits/group_member.h
> create mode 100644 posix/tst-group_member.c
> create mode 100644 sysdeps/unix/sysv/linux/bits/group_member.h
There are __group_member calls in sysdeps/posix/euidaccess.c and
sysdeps/unix/sysv/linux/faccessat.c. We can return ENOMEM in those
cases. Furthermore, euidaccess should really be layered on top of
faccessat (and use kernel support for AT_EACCESS if available).
Those are separate changes, but necessary to avoid exposing the alloca
path to non-deprecated functionality.
Thanks,
Florian
On Tue, Oct 17, 2023 at 04:00:00PM +0200, Florian Weimer wrote:
> * 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 a testcase.
> > ---
> > Changes to v2:
> > * Move the linux group_member.h to the bits directory
> > * Include the correct group_member.h in posix/unistd.h
> >
> > NEWS | 5 ++-
> > bits/group_member.h | 31 ++++++++++++++++
> > posix/Makefile | 4 ++
> > posix/tst-group_member.c | 41 +++++++++++++++++++++
> > posix/unistd.h | 6 +--
> > sysdeps/unix/sysv/linux/bits/group_member.h | 32 ++++++++++++++++
> > 6 files changed, 115 insertions(+), 4 deletions(-)
> > create mode 100644 bits/group_member.h
> > create mode 100644 posix/tst-group_member.c
> > create mode 100644 sysdeps/unix/sysv/linux/bits/group_member.h
>
> There are __group_member calls in sysdeps/posix/euidaccess.c and
> sysdeps/unix/sysv/linux/faccessat.c. We can return ENOMEM in those
> cases. Furthermore, euidaccess should really be layered on top of
> faccessat (and use kernel support for AT_EACCESS if available).
>
> Those are separate changes, but necessary to avoid exposing the alloca
> path to non-deprecated functionality.
Thanks for pointing those out. So are you suggesting that I perhaps do
need to create an internal only __group_member2 that uses malloc or a
scratch_buffer?
Thanks,
Joe
* Joe Simmons-Talbott:
>> There are __group_member calls in sysdeps/posix/euidaccess.c and
>> sysdeps/unix/sysv/linux/faccessat.c. We can return ENOMEM in those
>> cases. Furthermore, euidaccess should really be layered on top of
>> faccessat (and use kernel support for AT_EACCESS if available).
>>
>> Those are separate changes, but necessary to avoid exposing the alloca
>> path to non-deprecated functionality.
>
> Thanks for pointing those out. So are you suggesting that I perhaps do
> need to create an internal only __group_member2 that uses malloc or a
> scratch_buffer?
Yes, I think that would be prudent.
Thanks,
Florian
On Tue, Dec 12, 2023 at 12:51:28PM +0100, Florian Weimer wrote:
> * Joe Simmons-Talbott:
>
> >> There are __group_member calls in sysdeps/posix/euidaccess.c and
> >> sysdeps/unix/sysv/linux/faccessat.c. We can return ENOMEM in those
> >> cases. Furthermore, euidaccess should really be layered on top of
> >> faccessat (and use kernel support for AT_EACCESS if available).
> >>
> >> Those are separate changes, but necessary to avoid exposing the alloca
> >> path to non-deprecated functionality.
> >
> > Thanks for pointing those out. So are you suggesting that I perhaps do
> > need to create an internal only __group_member2 that uses malloc or a
> > scratch_buffer?
>
> Yes, I think that would be prudent.
I've added an internal only implentation as __group_member2 that uses
a scratch_buffer. I updated sysdeps/unix/sysv/linux/faccessat.c and
sysdeps/posix/euidaccess.c to use __group_member2 and return -1 on
memory allocation failure. I also added a testcase to test __group_member2.
This is all in v6 of the patch. [1]
Thanks,
Joe
[1] https://sourceware.org/pipermail/libc-alpha/2023-December/153266.html
@@ -40,7 +40,10 @@ Major new features:
Deprecated and removed features, and other changes affecting compatibility:
- [Add deprecations, removals and changes affecting compatibility here]
+* 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:
new file mode 100644
@@ -0,0 +1,31 @@
+/* group_member declaration
+ Copyright (C) 2023 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 _GROUP_MEMBER_H
+#define _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 /* GROUP_MEMBER_H */
@@ -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 \
@@ -294,6 +295,7 @@ tests := \
tst-glob_symlinks \
tst-gnuglob \
tst-gnuglob64 \
+ tst-group_member \
tst-mmap \
tst-mmap-offset \
tst-nanosleep \
@@ -615,6 +617,8 @@ 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)
new file mode 100644
@@ -0,0 +1,41 @@
+/* Basic tests for group_member.
+ Copyright (C) 2023 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>
@@ -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
new file mode 100644
@@ -0,0 +1,32 @@
+/* group_member declaration
+ Copyright (C) 2023 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 _GROUP_MEMBER_H
+#define _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 /* GROUP_MEMBER_H */