tmpfs: fix mounts when size is less than the page size

When tmpfs is mounted with a size less than one page, the number of blocks
is set to 0 which makes the tmpfs mount unlimited.  This can lead to a
quick and surprising death if someone typos a tmpfs mount command and
writes too much.

tmpfs can still be mounted as unlimited if size or nr_blocks is exactly 0,
as Documentation/filesystems/tmpfs.txt says.

Hugh: do this by rounding size up instead of down in all cases: which
slightly expands other odd-sized tmpfs mounts, but in a consistent way.

Signed-off-by: Michael Marineau <mike@marineau.org>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index ce64b6616376..7be94342bf06 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2012,7 +2012,7 @@ static int shmem_parse_options(char *options, int *mode, uid_t *uid,
                         }
                         if (*rest)
                                 goto bad_val;
-                        *blocks = size >> PAGE_CACHE_SHIFT;
+                        *blocks = DIV_ROUND_UP(size, PAGE_CACHE_SIZE);
                 } else if (!strcmp(this_char,"nr_blocks")) {
                         *blocks = memparse(value,&rest);
                         if (*rest)