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@xxxxxxxxxx>
---
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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