From ca880420665dbc8beec3693bee9f5eccb89de4a6 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Fri, 28 Dec 2018 00:34:43 -0800 Subject: [PATCH] userfaultfd: convert userfaultfd_ctx::refcount to refcount_t Reference counters should use refcount_t rather than atomic_t, since the refcount_t implementation can prevent overflows, reducing the exploitability of reference leak bugs. userfaultfd_ctx::refcount is a reference counter with the usual semantics, so convert it to refcount_t. Note: I replaced the BUG() on incrementing a 0 refcount with just refcount_inc(), since part of the semantics of refcount_t is that that incrementing a 0 refcount is not allowed; with CONFIG_REFCOUNT_FULL, refcount_inc() already checks for it and warns. Link: http://lkml.kernel.org/r/20181115003916.63381-1-ebiggers@kernel.org Signed-off-by: Eric Biggers Reviewed-by: Andrew Morton Cc: Andrea Arcangeli Reviewed-by: Mike Rapoport Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/userfaultfd.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 59dc28047030..e211b99d33c4 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -53,7 +53,7 @@ struct userfaultfd_ctx { /* a refile sequence protected by fault_pending_wqh lock */ struct seqcount refile_seq; /* pseudo fd refcounting */ - atomic_t refcount; + refcount_t refcount; /* userfaultfd syscall flags */ unsigned int flags; /* features requested from the userspace */ @@ -140,8 +140,7 @@ out: */ static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) { - if (!atomic_inc_not_zero(&ctx->refcount)) - BUG(); + refcount_inc(&ctx->refcount); } /** @@ -154,7 +153,7 @@ static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) */ static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) { - if (atomic_dec_and_test(&ctx->refcount)) { + if (refcount_dec_and_test(&ctx->refcount)) { VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock)); VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh)); VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock)); @@ -686,7 +685,7 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs) return -ENOMEM; } - atomic_set(&ctx->refcount, 1); + refcount_set(&ctx->refcount, 1); ctx->flags = octx->flags; ctx->state = UFFD_STATE_RUNNING; ctx->features = octx->features; @@ -1927,7 +1926,7 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) if (!ctx) return -ENOMEM; - atomic_set(&ctx->refcount, 1); + refcount_set(&ctx->refcount, 1); ctx->flags = flags; ctx->features = 0; ctx->state = UFFD_STATE_WAIT_API;