[PATCH] select: don't overflow if (SELECT_STACK_ALLOC % sizeof(long) != 0)
If SELECT_STACK_ALLOC is not a multiple of sizeof(long) then stack_fds[]
would be shorter than SELECT_STACK_ALLOC bytes and could overflow later in
the function. Fixed by simply rearranging the test later to work on
sizeof(stack_fds) Currently SELECT_STACK_ALLOC is 256 so this doesn't
happen, but it's nasty to have things like this hidden in the code. What
if later someone decides to change SELECT_STACK_ALLOC to 300?
Signed-off-by: Mitchell Blank Jr <mitch@sfgoth.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/select.c b/fs/select.c
index fce0fd1..a8109ba 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -311,7 +311,8 @@
{
fd_set_bits fds;
void *bits;
- int ret, size, max_fdset;
+ int ret, max_fdset;
+ unsigned int size;
struct fdtable *fdt;
/* Allocate small arguments on the stack to save memory and be faster */
long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
@@ -333,14 +334,15 @@
* since we used fdset we need to allocate memory in units of
* long-words.
*/
- ret = -ENOMEM;
size = FDS_BYTES(n);
- if (6*size < SELECT_STACK_ALLOC)
- bits = stack_fds;
- else
+ bits = stack_fds;
+ if (size > sizeof(stack_fds) / 6) {
+ /* Not enough space in on-stack array; must use kmalloc */
+ ret = -ENOMEM;
bits = kmalloc(6 * size, GFP_KERNEL);
- if (!bits)
- goto out_nofds;
+ if (!bits)
+ goto out_nofds;
+ }
fds.in = bits;
fds.out = bits + size;
fds.ex = bits + 2*size;