diff mbox series

[v5] ifaddrs: Get rid of alloca

Message ID 20230601164326.3697401-1-josimmon@redhat.com
State New
Headers show
Series [v5] ifaddrs: Get rid of alloca | expand

Commit Message

Joe Simmons-Talbott June 1, 2023, 4:43 p.m. UTC 
Use scratch_buffer and malloc rather than alloca to avoid potential stack
overflows.
---
Changes to v4:
  * Don't use a cleanup handler.

 sysdeps/unix/sysv/linux/ifaddrs.c | 46 ++++++++++++++-----------------
 1 file changed, 20 insertions(+), 26 deletions(-)

Comments

Joe Simmons-Talbott June 9, 2023, 3:01 p.m. UTC | #1 
On Thu, Jun 01, 2023 at 12:43:26PM -0400, Joe Simmons-Talbott wrote:
> Use scratch_buffer and malloc rather than alloca to avoid potential stack
> overflows.

Ping.

Thanks,
Joe
> ---
> Changes to v4:
>   * Don't use a cleanup handler.
> 
>  sysdeps/unix/sysv/linux/ifaddrs.c | 46 ++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 26 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/ifaddrs.c b/sysdeps/unix/sysv/linux/ifaddrs.c
> index 184ee224cb..a10e8d9292 100644
> --- a/sysdeps/unix/sysv/linux/ifaddrs.c
> +++ b/sysdeps/unix/sysv/linux/ifaddrs.c
> @@ -16,13 +16,13 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <alloca.h>
>  #include <assert.h>
>  #include <errno.h>
>  #include <ifaddrs.h>
>  #include <net/if.h>
>  #include <netinet/in.h>
>  #include <netpacket/packet.h>
> +#include <scratch_buffer.h>
>  #include <stdbool.h>
>  #include <stdint.h>
>  #include <stdlib.h>
> @@ -131,26 +131,14 @@ __netlink_request (struct netlink_handle *h, int type)
>    ssize_t read_len;
>    bool done = false;
>  
> -#ifdef PAGE_SIZE
> -  /* Help the compiler optimize out the malloc call if PAGE_SIZE
> -     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
> -  const size_t buf_size = PAGE_SIZE;
> -#else
> -  const size_t buf_size = __getpagesize ();
> -#endif
> -  bool use_malloc = false;
> -  char *buf;
> -
> -  if (__libc_use_alloca (buf_size))
> -    buf = alloca (buf_size);
> -  else
> -    {
> -      buf = malloc (buf_size);
> -      if (buf != NULL)
> -	use_malloc = true;
> -      else
> -	goto out_fail;
> -    }
> +  /* Netlink requires that user buffer needs to be either 8kb or page size
> +     (whichever is bigger), however this has been changed over time and now
> +     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
> +     linux/include/linux/netlink.h).  */
> +  const size_t buf_size = 8192;
> +  char *buf = malloc (buf_size);
> +  if (buf == NULL)
> +    goto out_fail;
>  
>    struct iovec iov = { buf, buf_size };
>  
> @@ -229,13 +217,11 @@ __netlink_request (struct netlink_handle *h, int type)
>        h->end_ptr = nlm_next;
>      }
>  
> -  if (use_malloc)
> -    free (buf);
> +  free(buf);
>    return 0;
>  
>  out_fail:
> -  if (use_malloc)
> -    free (buf);
> +  free(buf);
>    return -1;
>  }
>  
> @@ -324,6 +310,8 @@ getifaddrs_internal (struct ifaddrs **ifap)
>    char *ifa_data_ptr;	/* Pointer to the unused part of memory for
>  				ifa_data.  */
>    int result = 0;
> +  struct scratch_buffer buf;
> +  scratch_buffer_init (&buf);
>  
>    *ifap = NULL;
>  
> @@ -425,7 +413,12 @@ getifaddrs_internal (struct ifaddrs **ifap)
>      }
>  
>    /* Table for mapping kernel index to entry in our list.  */
> -  map_newlink_data = alloca (newlink * sizeof (int));
> +  if (!scratch_buffer_set_array_size (&buf, 1, newlink * sizeof (int)))
> +    {
> +      result = -1;
> +      goto exit_free;
> +    }
> +  map_newlink_data = buf.data;
>    memset (map_newlink_data, '\xff', newlink * sizeof (int));
>  
>    ifa_data_ptr = (char *) &ifas[newlink + newaddr];
> @@ -820,6 +813,7 @@ getifaddrs_internal (struct ifaddrs **ifap)
>   exit_free:
>    __netlink_free_handle (&nh);
>    __netlink_close (&nh);
> +  scratch_buffer_free (&buf);
>  
>    return result;
>  }
> -- 
> 2.39.2
>
Adhemerval Zanella Netto June 12, 2023, 8:44 p.m. UTC | #2 
On 01/06/23 13:43, Joe Simmons-Talbott via Libc-alpha wrote:
> Use scratch_buffer and malloc rather than alloca to avoid potential stack
> overflows.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
> Changes to v4:
>   * Don't use a cleanup handler.
> 
>  sysdeps/unix/sysv/linux/ifaddrs.c | 46 ++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 26 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/ifaddrs.c b/sysdeps/unix/sysv/linux/ifaddrs.c
> index 184ee224cb..a10e8d9292 100644
> --- a/sysdeps/unix/sysv/linux/ifaddrs.c
> +++ b/sysdeps/unix/sysv/linux/ifaddrs.c
> @@ -16,13 +16,13 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <alloca.h>
>  #include <assert.h>
>  #include <errno.h>
>  #include <ifaddrs.h>
>  #include <net/if.h>
>  #include <netinet/in.h>
>  #include <netpacket/packet.h>
> +#include <scratch_buffer.h>
>  #include <stdbool.h>
>  #include <stdint.h>
>  #include <stdlib.h>
> @@ -131,26 +131,14 @@ __netlink_request (struct netlink_handle *h, int type)
>    ssize_t read_len;
>    bool done = false;
>  
> -#ifdef PAGE_SIZE
> -  /* Help the compiler optimize out the malloc call if PAGE_SIZE
> -     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
> -  const size_t buf_size = PAGE_SIZE;
> -#else
> -  const size_t buf_size = __getpagesize ();
> -#endif
> -  bool use_malloc = false;
> -  char *buf;
> -
> -  if (__libc_use_alloca (buf_size))
> -    buf = alloca (buf_size);
> -  else
> -    {
> -      buf = malloc (buf_size);
> -      if (buf != NULL)
> -	use_malloc = true;
> -      else
> -	goto out_fail;
> -    }
> +  /* Netlink requires that user buffer needs to be either 8kb or page size
> +     (whichever is bigger), however this has been changed over time and now
> +     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
> +     linux/include/linux/netlink.h).  */
> +  const size_t buf_size = 8192;
> +  char *buf = malloc (buf_size);
> +  if (buf == NULL)
> +    goto out_fail;
>  
>    struct iovec iov = { buf, buf_size };
>  
> @@ -229,13 +217,11 @@ __netlink_request (struct netlink_handle *h, int type)
>        h->end_ptr = nlm_next;
>      }
>  
> -  if (use_malloc)
> -    free (buf);
> +  free(buf);
>    return 0;
>  
>  out_fail:
> -  if (use_malloc)
> -    free (buf);
> +  free(buf);
>    return -1;
>  }
>  
> @@ -324,6 +310,8 @@ getifaddrs_internal (struct ifaddrs **ifap)
>    char *ifa_data_ptr;	/* Pointer to the unused part of memory for
>  				ifa_data.  */
>    int result = 0;
> +  struct scratch_buffer buf;
> +  scratch_buffer_init (&buf);
>  
>    *ifap = NULL;
>  
> @@ -425,7 +413,12 @@ getifaddrs_internal (struct ifaddrs **ifap)
>      }
>  
>    /* Table for mapping kernel index to entry in our list.  */
> -  map_newlink_data = alloca (newlink * sizeof (int));
> +  if (!scratch_buffer_set_array_size (&buf, 1, newlink * sizeof (int)))
> +    {
> +      result = -1;
> +      goto exit_free;
> +    }
> +  map_newlink_data = buf.data;
>    memset (map_newlink_data, '\xff', newlink * sizeof (int));
>  
>    ifa_data_ptr = (char *) &ifas[newlink + newaddr];
> @@ -820,6 +813,7 @@ getifaddrs_internal (struct ifaddrs **ifap)
>   exit_free:
>    __netlink_free_handle (&nh);
>    __netlink_close (&nh);
> +  scratch_buffer_free (&buf);
>  
>    return result;
>  }
Joe Simmons-Talbott June 14, 2023, 7:20 p.m. UTC | #3 
On Mon, Jun 12, 2023 at 05:44:19PM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 01/06/23 13:43, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use scratch_buffer and malloc rather than alloca to avoid potential stack
> > overflows.
> 
> LGTM, thanks.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Thanks for the review.  Would you mind pushing this please?

Thanks,
Joe
Joe Simmons-Talbott June 21, 2023, 5:17 p.m. UTC | #4 
On Wed, Jun 14, 2023 at 03:20:29PM -0400, Joe Simmons-Talbott via Libc-alpha wrote:
> On Mon, Jun 12, 2023 at 05:44:19PM -0300, Adhemerval Zanella Netto wrote:
> > 
> > 
> > On 01/06/23 13:43, Joe Simmons-Talbott via Libc-alpha wrote:
> > > Use scratch_buffer and malloc rather than alloca to avoid potential stack
> > > overflows.
> > 
> > LGTM, thanks.
> > 
> > Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
> 
> Thanks for the review.  Would you mind pushing this please?
> 

Ping.

Thanks,
Joe
Adhemerval Zanella Netto June 21, 2023, 7:14 p.m. UTC | #5 
On 01/06/23 13:43, Joe Simmons-Talbott via Libc-alpha wrote:
> Use scratch_buffer and malloc rather than alloca to avoid potential stack
> overflows.
> ---
> Changes to v4:
>   * Don't use a cleanup handler.
> 
>  sysdeps/unix/sysv/linux/ifaddrs.c | 46 ++++++++++++++-----------------
>  1 file changed, 20 insertions(+), 26 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/ifaddrs.c b/sysdeps/unix/sysv/linux/ifaddrs.c
> index 184ee224cb..a10e8d9292 100644
> --- a/sysdeps/unix/sysv/linux/ifaddrs.c
> +++ b/sysdeps/unix/sysv/linux/ifaddrs.c
> @@ -16,13 +16,13 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <alloca.h>
>  #include <assert.h>
>  #include <errno.h>
>  #include <ifaddrs.h>
>  #include <net/if.h>
>  #include <netinet/in.h>
>  #include <netpacket/packet.h>
> +#include <scratch_buffer.h>
>  #include <stdbool.h>
>  #include <stdint.h>
>  #include <stdlib.h>
> @@ -131,26 +131,14 @@ __netlink_request (struct netlink_handle *h, int type)
>    ssize_t read_len;
>    bool done = false;
>  
> -#ifdef PAGE_SIZE
> -  /* Help the compiler optimize out the malloc call if PAGE_SIZE
> -     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
> -  const size_t buf_size = PAGE_SIZE;
> -#else
> -  const size_t buf_size = __getpagesize ();
> -#endif
> -  bool use_malloc = false;
> -  char *buf;
> -
> -  if (__libc_use_alloca (buf_size))
> -    buf = alloca (buf_size);
> -  else
> -    {
> -      buf = malloc (buf_size);
> -      if (buf != NULL)
> -	use_malloc = true;
> -      else
> -	goto out_fail;
> -    }
> +  /* Netlink requires that user buffer needs to be either 8kb or page size
> +     (whichever is bigger), however this has been changed over time and now
> +     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
> +     linux/include/linux/netlink.h).  */
> +  const size_t buf_size = 8192;
> +  char *buf = malloc (buf_size);
> +  if (buf == NULL)
> +    goto out_fail;
>  
>    struct iovec iov = { buf, buf_size };
>  
> @@ -229,13 +217,11 @@ __netlink_request (struct netlink_handle *h, int type)
>        h->end_ptr = nlm_next;
>      }
>  
> -  if (use_malloc)
> -    free (buf);
> +  free(buf);
>    return 0;
>  
>  out_fail:
> -  if (use_malloc)
> -    free (buf);
> +  free(buf);
>    return -1;
>  }
>  
> @@ -324,6 +310,8 @@ getifaddrs_internal (struct ifaddrs **ifap)
>    char *ifa_data_ptr;	/* Pointer to the unused part of memory for
>  				ifa_data.  */
>    int result = 0;
> +  struct scratch_buffer buf;
> +  scratch_buffer_init (&buf);
>  
>    *ifap = NULL;
>  
> @@ -425,7 +413,12 @@ getifaddrs_internal (struct ifaddrs **ifap)
>      }
>  
>    /* Table for mapping kernel index to entry in our list.  */
> -  map_newlink_data = alloca (newlink * sizeof (int));
> +  if (!scratch_buffer_set_array_size (&buf, 1, newlink * sizeof (int)))

I just realized that this defeats the overflow checks done by 
__libc_scratch_buffer_set_array_size.  The correct usage is as:

  if (!scratch_buffer_set_array_size (&buf, newlink, sizeof (int)))
     [...]

Could you please send a new version so Siddhesh STATS script do not
scream at us?

> +    {
> +      result = -1;
> +      goto exit_free;
> +    }
> +  map_newlink_data = buf.data;
>    memset (map_newlink_data, '\xff', newlink * sizeof (int));
>  
>    ifa_data_ptr = (char *) &ifas[newlink + newaddr];
> @@ -820,6 +813,7 @@ getifaddrs_internal (struct ifaddrs **ifap)
>   exit_free:
>    __netlink_free_handle (&nh);
>    __netlink_close (&nh);
> +  scratch_buffer_free (&buf);
>  
>    return result;
>  }
Joe Simmons-Talbott June 21, 2023, 8:04 p.m. UTC | #6 
On Wed, Jun 21, 2023 at 04:14:11PM -0300, Adhemerval Zanella Netto wrote:
> 
> 
> On 01/06/23 13:43, Joe Simmons-Talbott via Libc-alpha wrote:
> > Use scratch_buffer and malloc rather than alloca to avoid potential stack
> > overflows.
> > ---
> > Changes to v4:
> >   * Don't use a cleanup handler.
> > 
> >  sysdeps/unix/sysv/linux/ifaddrs.c | 46 ++++++++++++++-----------------
> >  1 file changed, 20 insertions(+), 26 deletions(-)
> > 
> > diff --git a/sysdeps/unix/sysv/linux/ifaddrs.c b/sysdeps/unix/sysv/linux/ifaddrs.c
> > index 184ee224cb..a10e8d9292 100644
> > --- a/sysdeps/unix/sysv/linux/ifaddrs.c
> > +++ b/sysdeps/unix/sysv/linux/ifaddrs.c
> > @@ -16,13 +16,13 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >  
> > -#include <alloca.h>
> >  #include <assert.h>
> >  #include <errno.h>
> >  #include <ifaddrs.h>
> >  #include <net/if.h>
> >  #include <netinet/in.h>
> >  #include <netpacket/packet.h>
> > +#include <scratch_buffer.h>
> >  #include <stdbool.h>
> >  #include <stdint.h>
> >  #include <stdlib.h>
> > @@ -131,26 +131,14 @@ __netlink_request (struct netlink_handle *h, int type)
> >    ssize_t read_len;
> >    bool done = false;
> >  
> > -#ifdef PAGE_SIZE
> > -  /* Help the compiler optimize out the malloc call if PAGE_SIZE
> > -     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
> > -  const size_t buf_size = PAGE_SIZE;
> > -#else
> > -  const size_t buf_size = __getpagesize ();
> > -#endif
> > -  bool use_malloc = false;
> > -  char *buf;
> > -
> > -  if (__libc_use_alloca (buf_size))
> > -    buf = alloca (buf_size);
> > -  else
> > -    {
> > -      buf = malloc (buf_size);
> > -      if (buf != NULL)
> > -	use_malloc = true;
> > -      else
> > -	goto out_fail;
> > -    }
> > +  /* Netlink requires that user buffer needs to be either 8kb or page size
> > +     (whichever is bigger), however this has been changed over time and now
> > +     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
> > +     linux/include/linux/netlink.h).  */
> > +  const size_t buf_size = 8192;
> > +  char *buf = malloc (buf_size);
> > +  if (buf == NULL)
> > +    goto out_fail;
> >  
> >    struct iovec iov = { buf, buf_size };
> >  
> > @@ -229,13 +217,11 @@ __netlink_request (struct netlink_handle *h, int type)
> >        h->end_ptr = nlm_next;
> >      }
> >  
> > -  if (use_malloc)
> > -    free (buf);
> > +  free(buf);
> >    return 0;
> >  
> >  out_fail:
> > -  if (use_malloc)
> > -    free (buf);
> > +  free(buf);
> >    return -1;
> >  }
> >  
> > @@ -324,6 +310,8 @@ getifaddrs_internal (struct ifaddrs **ifap)
> >    char *ifa_data_ptr;	/* Pointer to the unused part of memory for
> >  				ifa_data.  */
> >    int result = 0;
> > +  struct scratch_buffer buf;
> > +  scratch_buffer_init (&buf);
> >  
> >    *ifap = NULL;
> >  
> > @@ -425,7 +413,12 @@ getifaddrs_internal (struct ifaddrs **ifap)
> >      }
> >  
> >    /* Table for mapping kernel index to entry in our list.  */
> > -  map_newlink_data = alloca (newlink * sizeof (int));
> > +  if (!scratch_buffer_set_array_size (&buf, 1, newlink * sizeof (int)))
> 
> I just realized that this defeats the overflow checks done by 
> __libc_scratch_buffer_set_array_size.  The correct usage is as:
> 
>   if (!scratch_buffer_set_array_size (&buf, newlink, sizeof (int)))
>      [...]
> 
> Could you please send a new version so Siddhesh STATS script do not
> scream at us?

I've sent a v6 with this fix.  Thanks for catching it.

Thanks,
Joe
diff mbox series

Patch

diff --git a/sysdeps/unix/sysv/linux/ifaddrs.c b/sysdeps/unix/sysv/linux/ifaddrs.c
index 184ee224cb..a10e8d9292 100644
--- a/sysdeps/unix/sysv/linux/ifaddrs.c
+++ b/sysdeps/unix/sysv/linux/ifaddrs.c
@@ -16,13 +16,13 @@ 
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <alloca.h>
 #include <assert.h>
 #include <errno.h>
 #include <ifaddrs.h>
 #include <net/if.h>
 #include <netinet/in.h>
 #include <netpacket/packet.h>
+#include <scratch_buffer.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -131,26 +131,14 @@  __netlink_request (struct netlink_handle *h, int type)
   ssize_t read_len;
   bool done = false;
 
-#ifdef PAGE_SIZE
-  /* Help the compiler optimize out the malloc call if PAGE_SIZE
-     is constant and smaller or equal to PTHREAD_STACK_MIN/4.  */
-  const size_t buf_size = PAGE_SIZE;
-#else
-  const size_t buf_size = __getpagesize ();
-#endif
-  bool use_malloc = false;
-  char *buf;
-
-  if (__libc_use_alloca (buf_size))
-    buf = alloca (buf_size);
-  else
-    {
-      buf = malloc (buf_size);
-      if (buf != NULL)
-	use_malloc = true;
-      else
-	goto out_fail;
-    }
+  /* Netlink requires that user buffer needs to be either 8kb or page size
+     (whichever is bigger), however this has been changed over time and now
+     8Kb is sufficient (check NLMSG_DEFAULT_SIZE on Linux
+     linux/include/linux/netlink.h).  */
+  const size_t buf_size = 8192;
+  char *buf = malloc (buf_size);
+  if (buf == NULL)
+    goto out_fail;
 
   struct iovec iov = { buf, buf_size };
 
@@ -229,13 +217,11 @@  __netlink_request (struct netlink_handle *h, int type)
       h->end_ptr = nlm_next;
     }
 
-  if (use_malloc)
-    free (buf);
+  free(buf);
   return 0;
 
 out_fail:
-  if (use_malloc)
-    free (buf);
+  free(buf);
   return -1;
 }
 
@@ -324,6 +310,8 @@  getifaddrs_internal (struct ifaddrs **ifap)
   char *ifa_data_ptr;	/* Pointer to the unused part of memory for
 				ifa_data.  */
   int result = 0;
+  struct scratch_buffer buf;
+  scratch_buffer_init (&buf);
 
   *ifap = NULL;
 
@@ -425,7 +413,12 @@  getifaddrs_internal (struct ifaddrs **ifap)
     }
 
   /* Table for mapping kernel index to entry in our list.  */
-  map_newlink_data = alloca (newlink * sizeof (int));
+  if (!scratch_buffer_set_array_size (&buf, 1, newlink * sizeof (int)))
+    {
+      result = -1;
+      goto exit_free;
+    }
+  map_newlink_data = buf.data;
   memset (map_newlink_data, '\xff', newlink * sizeof (int));
 
   ifa_data_ptr = (char *) &ifas[newlink + newaddr];
@@ -820,6 +813,7 @@  getifaddrs_internal (struct ifaddrs **ifap)
  exit_free:
   __netlink_free_handle (&nh);
   __netlink_close (&nh);
+  scratch_buffer_free (&buf);
 
   return result;
 }