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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 <ebiggers@google.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Biggers 2018-12-28 00:34:43 -08:00 committed by Linus Torvalds
parent 66f71da9dd
commit ca88042066
1 changed files with 5 additions and 6 deletions
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11
fs/userfaultfd.c
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@ -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;