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swapon: check validity of swap_flags

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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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2012-03-28 14:42:42 -07:00 committed by Linus Torvalds
parent 29fd66d289
commit d15cab9754
2 changed files with 6 additions and 0 deletions
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3
include/linux/swap.h
View File

@ -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;

3
mm/swapfile.c
View File

@ -2022,6 +2022,9 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
struct page *page = NULL;
struct inode *inode = NULL;
if (swap_flags & ~SWAP_FLAGS_VALID)
return -EINVAL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;