From: Joe Simmons-Talbott <josimmon@redhat.com>
To: libc-alpha@sourceware.org
Cc: Joe Simmons-Talbott <josimmon@redhat.com>
Subject: [PATCH v6] ifaddrs: Get rid of alloca
Date: Wed, 21 Jun 2023 16:00:53 -0400 [thread overview]
Message-ID: <20230621200053.3021604-1-josimmon@redhat.com> (raw)
Use scratch_buffer and malloc rather than alloca to avoid potential stack
overflows.
---
Changes to v5:
* Don't bypass the __libc_scratch_buffer_set_array_size check by
passing both the item size and count to scratch_buffer_set_array_size.
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..0db9bb7847 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, 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
next reply other threads:[~2023-06-21 20:01 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-21 20:00 Joe Simmons-Talbott [this message]
2023-06-22 13:47 ` Adhemerval Zanella Netto
2023-06-26 13:10 ` Siddhesh Poyarekar
2023-06-26 19:49 ` Adhemerval Zanella Netto
2023-06-26 21:04 ` Joe Simmons-Talbott
2023-06-27 11:50 ` Siddhesh Poyarekar
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