coredump: Proactively round up to kmalloc bucket size

Instead of discovering the kmalloc bucket size _after_ allocation, round
up proactively so the allocation is explicitly made for the full size,
allowing the compiler to correctly reason about the resulting size of
the buffer through the existing __alloc_size() hint.

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/fs/coredump.c b/fs/coredump.c
index 7bad7785e8e675ac92d5ba6f55bec90658e4ca51..97eaee3252515003203a553176c8485c165949c6 100644 (file)
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -68,7 +68,10 @@ struct core_name {
 
 static int expand_corename(struct core_name *cn, int size)
 {
-       char *corename = krealloc(cn->corename, size, GFP_KERNEL);
+       char *corename;
+
+       size = kmalloc_size_roundup(size);
+       corename = krealloc(cn->corename, size, GFP_KERNEL);
 
        if (!corename)
                return -ENOMEM;
@@ -76,7 +79,7 @@ static int expand_corename(struct core_name *cn, int size)
        if (size > core_name_size) /* racy but harmless */
                core_name_size = size;
 
-       cn->size = ksize(corename);
+       cn->size = size;
        cn->corename = corename;
        return 0;
 }