[Xen-devel] [PATCH 1/2] libs/gnttab: do not use alloca(3)

[Wei Liu <wei.liu2@xxxxxxxxxx>]

The semantics of alloca(3) is not very nice. If the stack overflows,
program behaviour is undefined.

Remove the use of alloca(3) and always use mmap.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libs/gnttab/linux.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/tools/libs/gnttab/linux.c b/tools/libs/gnttab/linux.c
index 7b0fba4..535ce34 100644
--- a/tools/libs/gnttab/linux.c
+++ b/tools/libs/gnttab/linux.c
@@ -102,18 +102,12 @@ void *osdep_gnttab_grant_map(xengnttab_handle *xgt,
     if (flags & XENGNTTAB_GRANT_MAP_SINGLE_DOMAIN)
         domids_stride = 0;
 
-    if ( map_size <= PAGE_SIZE )
-        map = alloca(sizeof(*map) +
-                     (count - 1) * sizeof(struct ioctl_gntdev_map_grant_ref));
-    else
+    map = mmap(NULL, map_size, PROT_READ | PROT_WRITE,
+               MAP_PRIVATE | MAP_ANON | MAP_POPULATE, -1, 0);
+    if ( map == MAP_FAILED )
     {
-        map = mmap(NULL, map_size, PROT_READ | PROT_WRITE,
-                   MAP_PRIVATE | MAP_ANON | MAP_POPULATE, -1, 0);
-        if ( map == MAP_FAILED )
-        {
-            GTERROR(xgt->logger, "mmap of map failed");
-            return NULL;
-        }
+        GTERROR(xgt->logger, "mmap of map failed");
+        return NULL;
     }
 
     for ( i = 0; i < count; i++ )
@@ -187,8 +181,7 @@ void *osdep_gnttab_grant_map(xengnttab_handle *xgt,
     }
 
  out:
-    if ( map_size > PAGE_SIZE )
-        munmap(map, map_size);
+    munmap(map, map_size);
 
     return addr;
 }
-- 
2.1.4


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