Prevent tmpfs instances mounted in an unprivileged namespaces from evading accounting of locked memory by using the "noswap" mount option. Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx> Link: https://lore.kernel.org/lkml/79eae9fe-7818-a65c-89c6-138b55d609a@xxxxxxxxxx Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> --- mm/shmem.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 787e83791eb5..21ce9b26bb4d 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3571,6 +3571,10 @@ static int shmem_parse_one(struct fs_context *fc, struct fs_parameter *param) ctx->seen |= SHMEM_SEEN_INUMS; break; case Opt_noswap: + if ((fc->user_ns != &init_user_ns) || !capable(CAP_SYS_ADMIN)) { + return invalfc(fc, + "Turning off swap in unprivileged tmpfs mounts unsupported"); + } ctx->noswap = true; ctx->seen |= SHMEM_SEEN_NOSWAP; break; -- 2.34.1
