* [PATCH] userfaultfd: convert userfaultfd_ctx::refcount to refcount_t
@ 2018-11-15 0:39 Eric Biggers
2018-11-21 17:42 ` Mike Rapoport
0 siblings, 1 reply; 3+ messages in thread
From: Eric Biggers @ 2018-11-15 0:39 UTC (permalink / raw)
To: linux-mm, Andrew Morton; +Cc: Andrea Arcangeli, linux-kernel
From: Eric Biggers <ebiggers@google.com>
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.
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/userfaultfd.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 356d2b8568c14..8375faac2790d 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 @@ static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
*/
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;
@@ -1911,7 +1910,7 @@ 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;
--
2.19.1.930.g4563a0d9d0-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] userfaultfd: convert userfaultfd_ctx::refcount to refcount_t
2018-11-15 0:39 [PATCH] userfaultfd: convert userfaultfd_ctx::refcount to refcount_t Eric Biggers
@ 2018-11-21 17:42 ` Mike Rapoport
0 siblings, 0 replies; 3+ messages in thread
From: Mike Rapoport @ 2018-11-21 17:42 UTC (permalink / raw)
To: Eric Biggers; +Cc: linux-mm, Andrew Morton, Andrea Arcangeli, linux-kernel
On Wed, Nov 14, 2018 at 04:39:16PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> 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.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> fs/userfaultfd.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 356d2b8568c14..8375faac2790d 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 @@ static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
> */
> 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;
> @@ -1911,7 +1910,7 @@ 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;
> --
> 2.19.1.930.g4563a0d9d0-goog
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH] userfaultfd: convert userfaultfd_ctx::refcount to refcount_t
@ 2018-11-15 0:36 Eric Biggers
0 siblings, 0 replies; 3+ messages in thread
From: Eric Biggers @ 2018-11-15 0:36 UTC (permalink / raw)
To: linux-mm, Andrew Morton; +Cc: Andrea Arcangeli, linux-kernel
From: Eric Biggers <ebiggers@google.com>
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 already part of the semantics of refcount_t is
that that incrementing a 0 refcount is not allowed; with
CONFIG_REFCOUNT_FULL, refcount_inc() checks for it and warns.
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/userfaultfd.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 356d2b8568c14..8375faac2790d 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 @@ static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
*/
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;
@@ -1911,7 +1910,7 @@ 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;
--
2.19.1.930.g4563a0d9d0-goog
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2018-11-21 17:42 ` Mike Rapoport
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