Re: [Qemu-devel] [PATCH] target-ppc: kvm: Fix memory overflow issue about strncat()

[Chen Gang <gang.chen.5i5j@gmail.com>]

On 10/13/14 22:47, Alexander Graf wrote:
> 
> Could you please instead rewrite it to use g_strdup_printf() rather than
> strncat()s? That way we resolve all string pitfalls automatically - and
> this code is not the fast path, so doing an extra memory allocation is ok.
>

I guess, it is a personal taste. For me, it may need additional variable
for g_strdup_printf(), and not save code lines, but *sprintf() is more
readable than str*cat().

The related code may like below (welcome any improvement for it):

diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
index 66e7ce5..cea6a87 100644
--- a/target-ppc/kvm.c
+++ b/target-ppc/kvm.c
@@ -1782,7 +1782,7 @@ static int kvmppc_find_cpu_dt(char *buf, int buf_len)
  * format) */
 static uint64_t kvmppc_read_int_cpu_dt(const char *propname)
 {
-    char buf[PATH_MAX];
+    char buf[PATH_MAX], *tmp;
     union {
         uint32_t v32;
         uint64_t v64;
@@ -1794,10 +1794,10 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname)
         return -1;
     }
 
-    strncat(buf, "/", sizeof(buf) - strlen(buf) - 1);
-    strncat(buf, propname, sizeof(buf) - strlen(buf) - 1);
+    tmp = g_strdup_printf("%s/%s", buf, propname);
 
-    f = fopen(buf, "rb");
+    f = fopen(tmp, "rb");
+    g_free(buf);
     if (!f) {
         return -1;
     }

For me, it is really a personal taste, so if the maintainer feels the
diff above is OK, I shall send patch v2 for it within 2 days.


Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed