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[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>
This commit is contained in:
Mitchell Blank Jr 2006-04-10 22:54:08 -07:00 committed by Linus Torvalds
parent a9cdf410ca
commit b04eb6aa08
1 changed files with 9 additions and 7 deletions
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16
fs/select.c
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@ -311,7 +311,8 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
{
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 @@ static int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
* 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;