mm/mempolicy.c: make copy_from_user() provably correct

When compiling mm/mempolicy.c with struct user copy checks the following
warning is shown:

  In file included from arch/x86/include/asm/uaccess.h:572,
                   from include/linux/uaccess.h:5,
                   from include/linux/highmem.h:7,
                   from include/linux/pagemap.h:10,
                   from include/linux/mempolicy.h:70,
                   from mm/mempolicy.c:68:
  In function `copy_from_user',
      inlined from `compat_sys_get_mempolicy' at mm/mempolicy.c:1415:
  arch/x86/include/asm/uaccess_64.h:64: warning: call to `copy_from_user_overflow' declared with attribute warning: copy_from_user() buffer size is not provably correct
    LD      mm/built-in.o

Fix this by passing correct buffer size value.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b1f70d6eec35af18b96bf5b3b85f98c9ce4fdeba..9c51f9f58cacc8d4a9c9f363fd5f8778ebfac190 100644 (file)
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1411,7 +1411,9 @@ asmlinkage long compat_sys_get_mempolicy(int __user *policy,
        err = sys_get_mempolicy(policy, nm, nr_bits+1, addr, flags);
 
        if (!err && nmask) {
-               err = copy_from_user(bm, nm, alloc_size);
+               unsigned long copy_size;
+               copy_size = min_t(unsigned long, sizeof(bm), alloc_size);
+               err = copy_from_user(bm, nm, copy_size);
                /* ensure entire bitmap is zeroed */
                err |= clear_user(nmask, ALIGN(maxnode-1, 8) / 8);
                err |= compat_put_bitmap(nmask, bm, nr_bits);