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From fda365a53074f97f3213caefe70ea13297acecb2 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 2 Nov 2015 16:37:51 -0500
Subject: [PATCH] fix mremap memory synchronization and use of variadic
argument
since mremap with the MREMAP_FIXED flag is an operation that unmaps
existing mappings, it needs to use the vm lock mechanism to ensure
that any in-progress synchronization operations using vm identities
from before the call have finished.
also, the variadic argument was erroneously being read even if the
MREMAP_FIXED flag was not passed. in practice this didn't break
anything, but it's UB and in theory LTO could turn it into a hard
error.
---
src/mman/mremap.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/src/mman/mremap.c b/src/mman/mremap.c
index 1096ace..ce4e8ea 100644
--- a/src/mman/mremap.c
+++ b/src/mman/mremap.c
@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
#include <unistd.h>
#include <sys/mman.h>
#include <errno.h>
@@ -6,19 +7,25 @@
#include "syscall.h"
#include "libc.h"
+static void dummy(void) { }
+weak_alias(dummy, __vm_wait);
+
void *__mremap(void *old_addr, size_t old_len, size_t new_len, int flags, ...)
{
va_list ap;
- void *new_addr;
+ void *new_addr = 0;
if (new_len >= PTRDIFF_MAX) {
errno = ENOMEM;
return MAP_FAILED;
}
- va_start(ap, flags);
- new_addr = va_arg(ap, void *);
- va_end(ap);
+ if (flags & MREMAP_FIXED) {
+ __vm_wait();
+ va_start(ap, flags);
+ new_addr = va_arg(ap, void *);
+ va_end(ap);
+ }
return (void *)syscall(SYS_mremap, old_addr, old_len, new_len, flags, new_addr);
}
--
2.7.0
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