From: Siddhesh Poyarekar <siddhesh@gotplt.org>
To: Arjun Shankar <arjun@redhat.com>, libc-alpha@sourceware.org
Subject: Re: [PATCH v4] socket: Check lengths before advancing pointer in CMSG_NXTHDR
Date: Fri, 29 Jul 2022 12:40:43 -0400 [thread overview]
Message-ID: <a2352da1-09ee-00f8-ac57-45c3a5a1f30f@gotplt.org> (raw)
In-Reply-To: <20220729132637.1693027-1-arjun@redhat.com>
On 2022-07-29 09:26, Arjun Shankar wrote:
> The inline and library functions that the CMSG_NXTHDR macro may expand
> to increment the pointer to the header before checking the stride of
> the increment against available space. Since C only allows incrementing
> pointers to one past the end of an array, the increment must be done
> after a length check. This commit fixes that and includes a regression
> test for CMSG_FIRSTHDR and CMSG_NXTHDR.
>
> The Linux, Hurd, and generic headers are all changed.
>
> Tested on Linux on armv7hl, i686, x86_64, aarch64, ppc64le, and s390x.
>
> [BZ #28846]
> ---
> v3: https://sourceware.org/pipermail/libc-alpha/2022-July/140854.html
>
> Notes on v4:
>
> * Addressed review comments from Siddhesh:
>
> 1. (sizeof (struct cmsghdr) + __CMSG_PADDING (cmsg_len)):
> defined as size_needed.
>
> 2.
>> OK, but I wonder if there's utility in making the padding a generic
>> macro, e.g.
>
>> #define ALIGN_PADDING(n, a) ((a - (n & (a - 1))) & (a - 1))
>
> This sounds useful, and actually it would be great to move *all* of the
> duplicate code between these versions into a separate file and include it
> in these variants. I'll try to do a follow-up with this soon. I'm going to
> note it down in my TODO.
>
> 3.
>> __msg_control_ptr doesn't really need the __ since it's a local variable.
>
> I thought so too. But Florian pointed out that it would interfere with
> things like users #define'ing msg_control_ptr before including socket.h.
> ---
> bits/socket.h | 40 ++++++++++--
> socket/Makefile | 1 +
> socket/tst-cmsghdr-skeleton.c | 92 +++++++++++++++++++++++++++
> socket/tst-cmsghdr.c | 56 ++++++++++++++++
> sysdeps/mach/hurd/bits/socket.h | 40 ++++++++++--
> sysdeps/unix/sysv/linux/bits/socket.h | 40 ++++++++++--
> sysdeps/unix/sysv/linux/cmsg_nxthdr.c | 36 ++++++++---
> 7 files changed, 276 insertions(+), 29 deletions(-)
> create mode 100644 socket/tst-cmsghdr-skeleton.c
> create mode 100644 socket/tst-cmsghdr.c
LGTM.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
>
> diff --git a/bits/socket.h b/bits/socket.h
> index 2b99dea33b..aac8c49b00 100644
> --- a/bits/socket.h
> +++ b/bits/socket.h
> @@ -245,6 +245,12 @@ struct cmsghdr
> + CMSG_ALIGN (sizeof (struct cmsghdr)))
> #define CMSG_LEN(len) (CMSG_ALIGN (sizeof (struct cmsghdr)) + (len))
>
> +/* Given a length, return the additional padding necessary such that
> + len + __CMSG_PADDING(len) == CMSG_ALIGN (len). */
> +#define __CMSG_PADDING(len) ((sizeof (size_t) \
> + - ((len) & (sizeof (size_t) - 1))) \
> + & (sizeof (size_t) - 1))
> +
> extern struct cmsghdr *__cmsg_nxthdr (struct msghdr *__mhdr,
> struct cmsghdr *__cmsg) __THROW;
> #ifdef __USE_EXTERN_INLINES
> @@ -254,18 +260,38 @@ extern struct cmsghdr *__cmsg_nxthdr (struct msghdr *__mhdr,
> _EXTERN_INLINE struct cmsghdr *
> __NTH (__cmsg_nxthdr (struct msghdr *__mhdr, struct cmsghdr *__cmsg))
> {
> + /* We may safely assume that __cmsg lies between __mhdr->msg_control and
> + __mhdr->msg_controllen because the user is required to obtain the first
> + cmsg via CMSG_FIRSTHDR, set its length, then obtain subsequent cmsgs
> + via CMSG_NXTHDR, setting lengths along the way. However, we don't yet
> + trust the value of __cmsg->cmsg_len and therefore do not use it in any
> + pointer arithmetic until we check its value. */
> +
> + unsigned char * __msg_control_ptr = (unsigned char *) __mhdr->msg_control;
> + unsigned char * __cmsg_ptr = (unsigned char *) __cmsg;
> +
> + size_t __size_needed = sizeof (struct cmsghdr)
> + + __CMSG_PADDING (__cmsg->cmsg_len);
> +
> + /* The current header is malformed, too small to be a full header. */
> if ((size_t) __cmsg->cmsg_len < sizeof (struct cmsghdr))
> - /* The kernel header does this so there may be a reason. */
> return (struct cmsghdr *) 0;
>
> + /* There isn't enough space between __cmsg and the end of the buffer to
> + hold the current cmsg *and* the next one. */
> + if (((size_t)
> + (__msg_control_ptr + __mhdr->msg_controllen - __cmsg_ptr)
> + < __size_needed)
> + || ((size_t)
> + (__msg_control_ptr + __mhdr->msg_controllen - __cmsg_ptr
> + - __size_needed)
> + < __cmsg->cmsg_len))
> +
> + return (struct cmsghdr *) 0;
> +
> + /* Now, we trust cmsg_len and can use it to find the next header. */
> __cmsg = (struct cmsghdr *) ((unsigned char *) __cmsg
> + CMSG_ALIGN (__cmsg->cmsg_len));
> - if ((unsigned char *) (__cmsg + 1) > ((unsigned char *) __mhdr->msg_control
> - + __mhdr->msg_controllen)
> - || ((unsigned char *) __cmsg + CMSG_ALIGN (__cmsg->cmsg_len)
> - > ((unsigned char *) __mhdr->msg_control + __mhdr->msg_controllen)))
> - /* No more entries. */
> - return (struct cmsghdr *) 0;
> return __cmsg;
> }
> #endif /* Use `extern inline'. */
> diff --git a/socket/Makefile b/socket/Makefile
> index 156eec6c85..2bde78387f 100644
> --- a/socket/Makefile
> +++ b/socket/Makefile
> @@ -34,6 +34,7 @@ routines := accept bind connect getpeername getsockname getsockopt \
> tests := \
> tst-accept4 \
> tst-sockopt \
> + tst-cmsghdr \
> # tests
>
> tests-internal := \
> diff --git a/socket/tst-cmsghdr-skeleton.c b/socket/tst-cmsghdr-skeleton.c
> new file mode 100644
> index 0000000000..4c6898569b
> --- /dev/null
> +++ b/socket/tst-cmsghdr-skeleton.c
> @@ -0,0 +1,92 @@
> +/* Test ancillary data header creation.
> + Copyright (C) 2022 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/>. */
> +
> +/* We use the preprocessor to generate the function/macro tests instead of
> + using indirection because having all the macro expansions alongside
> + each other lets the compiler warn us about suspicious pointer
> + arithmetic across subsequent CMSG_{FIRST,NXT}HDR expansions. */
> +
> +#include <stdint.h>
> +
> +#define RUN_TEST_CONCAT(suffix) run_test_##suffix
> +#define RUN_TEST_FUNCNAME(suffix) RUN_TEST_CONCAT (suffix)
> +
> +static void
> +RUN_TEST_FUNCNAME (CMSG_NXTHDR_IMPL) (void)
> +{
> + struct msghdr m = {0};
> + struct cmsghdr *cmsg;
> + char cmsgbuf[3 * CMSG_SPACE (sizeof (PAYLOAD))] = {0};
> +
> + m.msg_control = cmsgbuf;
> + m.msg_controllen = sizeof (cmsgbuf);
> +
> + /* First header should point to the start of the buffer. */
> + cmsg = CMSG_FIRSTHDR (&m);
> + TEST_VERIFY_EXIT ((char *) cmsg == cmsgbuf);
> +
> + /* If the first header length consumes the entire buffer, there is no
> + space remaining for additional headers. */
> + cmsg->cmsg_len = sizeof (cmsgbuf);
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg == NULL);
> +
> + /* The first header length is so big, using it would cause an overflow. */
> + cmsg = CMSG_FIRSTHDR (&m);
> + TEST_VERIFY_EXIT ((char *) cmsg == cmsgbuf);
> + cmsg->cmsg_len = SIZE_MAX;
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg == NULL);
> +
> + /* The first header leaves just enough space to hold another header. */
> + cmsg = CMSG_FIRSTHDR (&m);
> + TEST_VERIFY_EXIT ((char *) cmsg == cmsgbuf);
> + cmsg->cmsg_len = sizeof (cmsgbuf) - sizeof (struct cmsghdr);
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg != NULL);
> +
> + /* The first header leaves space but not enough for another header. */
> + cmsg = CMSG_FIRSTHDR (&m);
> + TEST_VERIFY_EXIT ((char *) cmsg == cmsgbuf);
> + cmsg->cmsg_len ++;
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg == NULL);
> +
> + /* The second header leaves just enough space to hold another header. */
> + cmsg = CMSG_FIRSTHDR (&m);
> + TEST_VERIFY_EXIT ((char *) cmsg == cmsgbuf);
> + cmsg->cmsg_len = CMSG_LEN (sizeof (PAYLOAD));
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg != NULL);
> + cmsg->cmsg_len = sizeof (cmsgbuf)
> + - CMSG_SPACE (sizeof (PAYLOAD)) /* First header. */
> + - sizeof (struct cmsghdr);
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg != NULL);
> +
> + /* The second header leaves space but not enough for another header. */
> + cmsg = CMSG_FIRSTHDR (&m);
> + TEST_VERIFY_EXIT ((char *) cmsg == cmsgbuf);
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg != NULL);
> + cmsg->cmsg_len ++;
> + cmsg = CMSG_NXTHDR_IMPL (&m, cmsg);
> + TEST_VERIFY_EXIT (cmsg == NULL);
> +
> + return;
> +}
> diff --git a/socket/tst-cmsghdr.c b/socket/tst-cmsghdr.c
> new file mode 100644
> index 0000000000..68c96d3c9d
> --- /dev/null
> +++ b/socket/tst-cmsghdr.c
> @@ -0,0 +1,56 @@
> +/* Test ancillary data header creation.
> + Copyright (C) 2022 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 <sys/socket.h>
> +#include <gnu/lib-names.h>
> +#include <support/xdlfcn.h>
> +#include <support/check.h>
> +
> +#define PAYLOAD "Hello, World!"
> +
> +/* CMSG_NXTHDR is a macro that calls an inline function defined in
> + bits/socket.h. In case the function cannot be inlined, libc.so carries
> + a copy. Both versions need to be tested. */
> +
> +#define CMSG_NXTHDR_IMPL CMSG_NXTHDR
> +#include "tst-cmsghdr-skeleton.c"
> +#undef CMSG_NXTHDR_IMPL
> +
> +static struct cmsghdr * (* cmsg_nxthdr) (struct msghdr *, struct cmsghdr *);
> +
> +#define CMSG_NXTHDR_IMPL cmsg_nxthdr
> +#include "tst-cmsghdr-skeleton.c"
> +#undef CMSG_NXTHDR_IMPL
> +
> +static int
> +do_test (void)
> +{
> + static void *handle;
> +
> + run_test_CMSG_NXTHDR ();
> +
> + handle = xdlopen (LIBC_SO, RTLD_LAZY);
> + cmsg_nxthdr = (struct cmsghdr * (*) (struct msghdr *, struct cmsghdr *))
> + xdlsym (handle, "__cmsg_nxthdr");
> +
> + run_test_cmsg_nxthdr ();
> +
> + return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/sysdeps/mach/hurd/bits/socket.h b/sysdeps/mach/hurd/bits/socket.h
> index 5b35ea81ec..70fce4fb27 100644
> --- a/sysdeps/mach/hurd/bits/socket.h
> +++ b/sysdeps/mach/hurd/bits/socket.h
> @@ -249,6 +249,12 @@ struct cmsghdr
> + CMSG_ALIGN (sizeof (struct cmsghdr)))
> #define CMSG_LEN(len) (CMSG_ALIGN (sizeof (struct cmsghdr)) + (len))
>
> +/* Given a length, return the additional padding necessary such that
> + len + __CMSG_PADDING(len) == CMSG_ALIGN (len). */
> +#define __CMSG_PADDING(len) ((sizeof (size_t) \
> + - ((len) & (sizeof (size_t) - 1))) \
> + & (sizeof (size_t) - 1))
> +
> extern struct cmsghdr *__cmsg_nxthdr (struct msghdr *__mhdr,
> struct cmsghdr *__cmsg) __THROW;
> #ifdef __USE_EXTERN_INLINES
> @@ -258,18 +264,38 @@ extern struct cmsghdr *__cmsg_nxthdr (struct msghdr *__mhdr,
> _EXTERN_INLINE struct cmsghdr *
> __NTH (__cmsg_nxthdr (struct msghdr *__mhdr, struct cmsghdr *__cmsg))
> {
> + /* We may safely assume that __cmsg lies between __mhdr->msg_control and
> + __mhdr->msg_controllen because the user is required to obtain the first
> + cmsg via CMSG_FIRSTHDR, set its length, then obtain subsequent cmsgs
> + via CMSG_NXTHDR, setting lengths along the way. However, we don't yet
> + trust the value of __cmsg->cmsg_len and therefore do not use it in any
> + pointer arithmetic until we check its value. */
> +
> + unsigned char * __msg_control_ptr = (unsigned char *) __mhdr->msg_control;
> + unsigned char * __cmsg_ptr = (unsigned char *) __cmsg;
> +
> + size_t __size_needed = sizeof (struct cmsghdr)
> + + __CMSG_PADDING (__cmsg->cmsg_len);
> +
> + /* The current header is malformed, too small to be a full header. */
> if ((size_t) __cmsg->cmsg_len < sizeof (struct cmsghdr))
> - /* The kernel header does this so there may be a reason. */
> return (struct cmsghdr *) 0;
>
> + /* There isn't enough space between __cmsg and the end of the buffer to
> + hold the current cmsg *and* the next one. */
> + if (((size_t)
> + (__msg_control_ptr + __mhdr->msg_controllen - __cmsg_ptr)
> + < __size_needed)
> + || ((size_t)
> + (__msg_control_ptr + __mhdr->msg_controllen - __cmsg_ptr
> + - __size_needed)
> + < __cmsg->cmsg_len))
> +
> + return (struct cmsghdr *) 0;
> +
> + /* Now, we trust cmsg_len and can use it to find the next header. */
> __cmsg = (struct cmsghdr *) ((unsigned char *) __cmsg
> + CMSG_ALIGN (__cmsg->cmsg_len));
> - if ((unsigned char *) (__cmsg + 1) > ((unsigned char *) __mhdr->msg_control
> - + __mhdr->msg_controllen)
> - || ((unsigned char *) __cmsg + CMSG_ALIGN (__cmsg->cmsg_len)
> - > ((unsigned char *) __mhdr->msg_control + __mhdr->msg_controllen)))
> - /* No more entries. */
> - return (struct cmsghdr *) 0;
> return __cmsg;
> }
> #endif /* Use `extern inline'. */
> diff --git a/sysdeps/unix/sysv/linux/bits/socket.h b/sysdeps/unix/sysv/linux/bits/socket.h
> index 4f1f810ea1..539b8d7716 100644
> --- a/sysdeps/unix/sysv/linux/bits/socket.h
> +++ b/sysdeps/unix/sysv/linux/bits/socket.h
> @@ -307,6 +307,12 @@ struct cmsghdr
> + CMSG_ALIGN (sizeof (struct cmsghdr)))
> #define CMSG_LEN(len) (CMSG_ALIGN (sizeof (struct cmsghdr)) + (len))
>
> +/* Given a length, return the additional padding necessary such that
> + len + __CMSG_PADDING(len) == CMSG_ALIGN (len). */
> +#define __CMSG_PADDING(len) ((sizeof (size_t) \
> + - ((len) & (sizeof (size_t) - 1))) \
> + & (sizeof (size_t) - 1))
> +
> extern struct cmsghdr *__cmsg_nxthdr (struct msghdr *__mhdr,
> struct cmsghdr *__cmsg) __THROW;
> #ifdef __USE_EXTERN_INLINES
> @@ -316,18 +322,38 @@ extern struct cmsghdr *__cmsg_nxthdr (struct msghdr *__mhdr,
> _EXTERN_INLINE struct cmsghdr *
> __NTH (__cmsg_nxthdr (struct msghdr *__mhdr, struct cmsghdr *__cmsg))
> {
> + /* We may safely assume that __cmsg lies between __mhdr->msg_control and
> + __mhdr->msg_controllen because the user is required to obtain the first
> + cmsg via CMSG_FIRSTHDR, set its length, then obtain subsequent cmsgs
> + via CMSG_NXTHDR, setting lengths along the way. However, we don't yet
> + trust the value of __cmsg->cmsg_len and therefore do not use it in any
> + pointer arithmetic until we check its value. */
> +
> + unsigned char * __msg_control_ptr = (unsigned char *) __mhdr->msg_control;
> + unsigned char * __cmsg_ptr = (unsigned char *) __cmsg;
> +
> + size_t __size_needed = sizeof (struct cmsghdr)
> + + __CMSG_PADDING (__cmsg->cmsg_len);
> +
> + /* The current header is malformed, too small to be a full header. */
> if ((size_t) __cmsg->cmsg_len < sizeof (struct cmsghdr))
> - /* The kernel header does this so there may be a reason. */
> return (struct cmsghdr *) 0;
>
> + /* There isn't enough space between __cmsg and the end of the buffer to
> + hold the current cmsg *and* the next one. */
> + if (((size_t)
> + (__msg_control_ptr + __mhdr->msg_controllen - __cmsg_ptr)
> + < __size_needed)
> + || ((size_t)
> + (__msg_control_ptr + __mhdr->msg_controllen - __cmsg_ptr
> + - __size_needed)
> + < __cmsg->cmsg_len))
> +
> + return (struct cmsghdr *) 0;
> +
> + /* Now, we trust cmsg_len and can use it to find the next header. */
> __cmsg = (struct cmsghdr *) ((unsigned char *) __cmsg
> + CMSG_ALIGN (__cmsg->cmsg_len));
> - if ((unsigned char *) (__cmsg + 1) > ((unsigned char *) __mhdr->msg_control
> - + __mhdr->msg_controllen)
> - || ((unsigned char *) __cmsg + CMSG_ALIGN (__cmsg->cmsg_len)
> - > ((unsigned char *) __mhdr->msg_control + __mhdr->msg_controllen)))
> - /* No more entries. */
> - return (struct cmsghdr *) 0;
> return __cmsg;
> }
> #endif /* Use `extern inline'. */
> diff --git a/sysdeps/unix/sysv/linux/cmsg_nxthdr.c b/sysdeps/unix/sysv/linux/cmsg_nxthdr.c
> index 15b7a3a925..24f72b797a 100644
> --- a/sysdeps/unix/sysv/linux/cmsg_nxthdr.c
> +++ b/sysdeps/unix/sysv/linux/cmsg_nxthdr.c
> @@ -23,18 +23,38 @@
> struct cmsghdr *
> __cmsg_nxthdr (struct msghdr *mhdr, struct cmsghdr *cmsg)
> {
> + /* We may safely assume that cmsg lies between mhdr->msg_control and
> + mhdr->msg_controllen because the user is required to obtain the first
> + cmsg via CMSG_FIRSTHDR, set its length, then obtain subsequent cmsgs
> + via CMSG_NXTHDR, setting lengths along the way. However, we don't yet
> + trust the value of cmsg->cmsg_len and therefore do not use it in any
> + pointer arithmetic until we check its value. */
> +
> + unsigned char * msg_control_ptr = (unsigned char *) mhdr->msg_control;
> + unsigned char * cmsg_ptr = (unsigned char *) cmsg;
> +
> + size_t size_needed = sizeof (struct cmsghdr)
> + + __CMSG_PADDING (cmsg->cmsg_len);
> +
> + /* The current header is malformed, too small to be a full header. */
> if ((size_t) cmsg->cmsg_len < sizeof (struct cmsghdr))
> - /* The kernel header does this so there may be a reason. */
> - return NULL;
> + return (struct cmsghdr *) 0;
> +
> + /* There isn't enough space between cmsg and the end of the buffer to
> + hold the current cmsg *and* the next one. */
> + if (((size_t)
> + (msg_control_ptr + mhdr->msg_controllen - cmsg_ptr)
> + < size_needed)
> + || ((size_t)
> + (msg_control_ptr + mhdr->msg_controllen - cmsg_ptr
> + - size_needed)
> + < cmsg->cmsg_len))
> +
> + return (struct cmsghdr *) 0;
>
> + /* Now, we trust cmsg_len and can use it to find the next header. */
> cmsg = (struct cmsghdr *) ((unsigned char *) cmsg
> + CMSG_ALIGN (cmsg->cmsg_len));
> - if ((unsigned char *) (cmsg + 1) > ((unsigned char *) mhdr->msg_control
> - + mhdr->msg_controllen)
> - || ((unsigned char *) cmsg + CMSG_ALIGN (cmsg->cmsg_len)
> - > ((unsigned char *) mhdr->msg_control + mhdr->msg_controllen)))
> - /* No more entries. */
> - return NULL;
> return cmsg;
> }
> libc_hidden_def (__cmsg_nxthdr)
next prev parent reply other threads:[~2022-07-29 16:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-29 13:26 Arjun Shankar
2022-07-29 16:40 ` Siddhesh Poyarekar [this message]
2022-07-29 16:43 ` Carlos O'Donell
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