[v4] 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 v3:
* Get rid of the 'out_fail' label and its respective gotos since we're
using a cleanup handler for the malloc'ed space.
sysdeps/unix/sysv/linux/ifaddrs.c | 64 +++++++++++++++----------------
1 file changed, 30 insertions(+), 34 deletions(-)
@@ -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)
{
@@ -131,31 +138,19 @@ __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 };
if (__netlink_sendreq (h, type) < 0)
- goto out_fail;
+ return -1;
while (! done)
{
@@ -173,13 +168,13 @@ __netlink_request (struct netlink_handle *h, int type)
read_len = TEMP_FAILURE_RETRY (__recvmsg (h->fd, &msg, 0));
__netlink_assert_response (h->fd, read_len);
if (read_len < 0)
- goto out_fail;
+ return -1;
if (nladdr.nl_pid != 0)
continue;
if (__glibc_unlikely (msg.msg_flags & MSG_TRUNC))
- goto out_fail;
+ return -1;
size_t count = 0;
size_t remaining_len = read_len;
@@ -205,7 +200,7 @@ __netlink_request (struct netlink_handle *h, int type)
errno = EIO;
else
errno = -nlerr->error;
- goto out_fail;
+ return -1;
}
}
@@ -217,7 +212,7 @@ __netlink_request (struct netlink_handle *h, int type)
nlm_next = (struct netlink_res *) malloc (sizeof (struct netlink_res)
+ read_len);
if (nlm_next == NULL)
- goto out_fail;
+ return -1;
nlm_next->next = NULL;
nlm_next->nlh = memcpy (nlm_next + 1, buf, read_len);
nlm_next->size = read_len;
@@ -229,14 +224,7 @@ __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 +312,8 @@ 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 +415,12 @@ 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 +815,7 @@ getifaddrs_internal (struct ifaddrs **ifap)
exit_free:
__netlink_free_handle (&nh);
__netlink_close (&nh);
+ scratch_buffer_free (&buf);
return result;
}