swapon: check validity of swap_flags

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>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index b86b5c20617d93e361d462e20c0c3c87856214b6..8dc0ea7caf02baa404e8896d13351577a177547a 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -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;

diff --git a/mm/swapfile.c b/mm/swapfile.c
index dae42f380d6ebcde88d3aaef6aa3cb1d64e0f5a3..fafc26d1b1dc885d2541eda3bdc5705a4fe56012 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -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;