* [PATCH] swapon: check validity of swap_flags
@ 2012-03-23 20:48 Hugh Dickins
2012-03-23 20:53 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Hugh Dickins @ 2012-03-23 20:48 UTC (permalink / raw)
To: Andrew Morton; +Cc: Al Viro, linux-kernel, linux-mm
Most system calls taking flags first check that the flags passed in are
valid, and that helps userspace to detect when new flags are supported.
But swapon never did so: start checking now, to help if we ever want to
support more swap_flags in future.
It's difficult to get stray bits set in an int, and swapon is not widely
used, so this is most unlikely to break any userspace; but we can just
revert if it turns out to do so.
Signed-off-by: Hugh Dickins <hughd@google.com>
---
include/linux/swap.h | 3 +++
mm/swapfile.c | 3 +++
2 files changed, 6 insertions(+)
--- linux.git/include/linux/swap.h 2012-03-23 10:19:53.408051631 -0700
+++ linux/include/linux/swap.h 2012-03-23 10:34:02.956071819 -0700
@@ -21,6 +21,9 @@ struct bio;
#define SWAP_FLAG_PRIO_SHIFT 0
#define SWAP_FLAG_DISCARD 0x10000 /* discard swap cluster after use */
+#define SWAP_FLAGS_VALID (SWAP_FLAG_PRIO_MASK | SWAP_FLAG_PREFER | \
+ SWAP_FLAG_DISCARD)
+
static inline int current_is_kswapd(void)
{
return current->flags & PF_KSWAPD;
--- linux.git/mm/swapfile.c 2012-03-23 10:19:53.588051635 -0700
+++ linux/mm/swapfile.c 2012-03-23 10:35:52.764074181 -0700
@@ -2022,6 +2022,9 @@ SYSCALL_DEFINE2(swapon, const char __use
struct page *page = NULL;
struct inode *inode = NULL;
+ if (swap_flags & ~SWAP_FLAGS_VALID)
+ return -EINVAL;
+
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
--
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* Re: [PATCH] swapon: check validity of swap_flags
2012-03-23 20:48 [PATCH] swapon: check validity of swap_flags Hugh Dickins
@ 2012-03-23 20:53 ` Andrew Morton
2012-03-23 21:20 ` Hugh Dickins
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2012-03-23 20:53 UTC (permalink / raw)
To: Hugh Dickins; +Cc: Al Viro, linux-kernel, linux-mm
On Fri, 23 Mar 2012 13:48:35 -0700 (PDT)
Hugh Dickins <hughd@google.com> wrote:
> Most system calls taking flags first check that the flags passed in are
> valid, and that helps userspace to detect when new flags are supported.
>
> But swapon never did so: start checking now, to help if we ever want to
> support more swap_flags in future.
>
> It's difficult to get stray bits set in an int, and swapon is not widely
> used, so this is most unlikely to break any userspace; but we can just
> revert if it turns out to do so.
It would be safer to emit a nasty message then let the swapon proceed
as before.
--
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] swapon: check validity of swap_flags
2012-03-23 20:53 ` Andrew Morton
@ 2012-03-23 21:20 ` Hugh Dickins
0 siblings, 0 replies; 3+ messages in thread
From: Hugh Dickins @ 2012-03-23 21:20 UTC (permalink / raw)
To: Andrew Morton; +Cc: Al Viro, linux-kernel, linux-mm
On Fri, 23 Mar 2012, Andrew Morton wrote:
> On Fri, 23 Mar 2012 13:48:35 -0700 (PDT)
> Hugh Dickins <hughd@google.com> wrote:
>
> > Most system calls taking flags first check that the flags passed in are
> > valid, and that helps userspace to detect when new flags are supported.
> >
> > But swapon never did so: start checking now, to help if we ever want to
> > support more swap_flags in future.
> >
> > It's difficult to get stray bits set in an int, and swapon is not widely
> > used, so this is most unlikely to break any userspace; but we can just
> > revert if it turns out to do so.
>
> It would be safer to emit a nasty message then let the swapon proceed
> as before.
Safer, I suppose, but I really don't expect that case to arise (we'll
have been doing those lovely runtime discards without asking for a year
now if so). And it does spoil the checking of supported flags.
Hugh
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