[v2] ifaddrs: Get rid of alloca
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Commit Message
Use scratch_buffer and malloc rather than alloca to avoid potential stack
overflows.
---
Changes to v1:
* in __netlink_request use an 8kb buffer size and malloc rather than a
scratch_buffer.
Suggested-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
sysdeps/unix/sysv/linux/ifaddrs.c | 51 +++++++++++++++----------------
1 file changed, 25 insertions(+), 26 deletions(-)
Comments
On 26/05/23 13:54, Joe Simmons-Talbott via Libc-alpha wrote:
> Use scratch_buffer and malloc rather than alloca to avoid potential stack
> overflows.
> ---
> Changes to v1:
> * in __netlink_request use an 8kb buffer size and malloc rather than a
> scratch_buffer.
>
> Suggested-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
>
> sysdeps/unix/sysv/linux/ifaddrs.c | 51 +++++++++++++++----------------
> 1 file changed, 25 insertions(+), 26 deletions(-)
>
> diff --git a/sysdeps/unix/sysv/linux/ifaddrs.c b/sysdeps/unix/sysv/linux/ifaddrs.c
> index 184ee224cb..e42da62e9b 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>
> @@ -122,6 +122,13 @@ __netlink_sendreq (struct netlink_handle *h, int type)
> }
>
>
> +static void
> +ifree (char **ptr)
> +{
> + free (*ptr);
> +}
> +
> +
> int
> __netlink_request (struct netlink_handle *h, int type)
> {
> @@ -131,26 +138,14 @@ __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 __attribute__ ((__cleanup__ (ifree))) = malloc (buf_size);
> + if (buf == NULL)
> + return -1;
>
> struct iovec iov = { buf, buf_size };
>
> @@ -229,13 +224,9 @@ __netlink_request (struct netlink_handle *h, int type)
> h->end_ptr = nlm_next;
> }
>
> - if (use_malloc)
> - free (buf);
> return 0;
>
> out_fail:
> - if (use_malloc)
> - free (buf);
> return -1;
> }
>
> @@ -324,6 +315,7 @@ 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;
Move the scratch_buffer_init here, otherwise previous failures (such as
the calloc) will trigger invalid memory access by the scratch_buffer_free.
The rest looks ok.
>
> *ifap = NULL;
>
> @@ -425,7 +417,13 @@ getifaddrs_internal (struct ifaddrs **ifap)
> }
>
> /* Table for mapping kernel index to entry in our list. */
> - map_newlink_data = alloca (newlink * sizeof (int));
> + scratch_buffer_init (&buf)> + 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 +818,7 @@ getifaddrs_internal (struct ifaddrs **ifap)
> exit_free:
> __netlink_free_handle (&nh);
> __netlink_close (&nh);
> + scratch_buffer_free (&buf);
>
> return result;
> }
@@ -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>
@@ -122,6 +122,13 @@ __netlink_sendreq (struct netlink_handle *h, int type)
}
+static void
+ifree (char **ptr)
+{
+ free (*ptr);
+}
+
+
int
__netlink_request (struct netlink_handle *h, int type)
{
@@ -131,26 +138,14 @@ __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 __attribute__ ((__cleanup__ (ifree))) = malloc (buf_size);
+ if (buf == NULL)
+ return -1;
struct iovec iov = { buf, buf_size };
@@ -229,13 +224,9 @@ __netlink_request (struct netlink_handle *h, int type)
h->end_ptr = nlm_next;
}
- if (use_malloc)
- free (buf);
return 0;
out_fail:
- if (use_malloc)
- free (buf);
return -1;
}
@@ -324,6 +315,7 @@ 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;
*ifap = NULL;
@@ -425,7 +417,13 @@ getifaddrs_internal (struct ifaddrs **ifap)
}
/* Table for mapping kernel index to entry in our list. */
- map_newlink_data = alloca (newlink * sizeof (int));
+ scratch_buffer_init (&buf);
+ 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 +818,7 @@ getifaddrs_internal (struct ifaddrs **ifap)
exit_free:
__netlink_free_handle (&nh);
__netlink_close (&nh);
+ scratch_buffer_free (&buf);
return result;
}