The file operations dereference the context pointer after checking status under ctx->status_mutex, then drop the lock before using the context. This allows afu_release() running on another CPU to free the context, leading to a use-after-free vulnerability.

The race window exists in afu_ioctl(), afu_mmap(), afu_poll() and afu_read() between the status check and context usage. During device hot-unplug or rapid open/close cycles, this causes kernel crashes.

Introduce reference counting via kref to prevent premature free. ocxl_context_get() atomically checks status and acquires a reference under status_mutex. File operations hold this reference for their duration, ensuring the context remains valid even if another thread calls afu_release().

ocxl_context_alloc() initializes refcount to 1 for the file's lifetime. afu_release() drops this reference, with the context freed when the last reference goes away. Preserve existing -EBUSY behavior where the context intentionally leaks on detach timeout.

Reported-by: Yuhao Jiang danisjiang@gmail.com Fixes: 5ef3166e8a32 ("ocxl: Driver code for 'generic' opencapi devices") Cc: stable@vger.kernel.org Signed-off-by: Yuhao Jiang danisjiang@gmail.com --- drivers/misc/ocxl/context.c | 69 ++++++++++++++---- drivers/misc/ocxl/file.c | 113 +++++++++++++++++++++++------- drivers/misc/ocxl/ocxl_internal.h | 4 ++ 3 files changed, 144 insertions(+), 42 deletions(-)

diff --git a/drivers/misc/ocxl/context.c b/drivers/misc/ocxl/context.c index cded7d1caf32..e154adc972a5 100644 --- a/drivers/misc/ocxl/context.c +++ b/drivers/misc/ocxl/context.c @@ -28,6 +28,7 @@ int ocxl_context_alloc(struct ocxl_context **context, struct ocxl_afu *afu,

ctx->pasid = pasid; ctx->status = OPENED; + kref_init(&ctx->kref); mutex_init(&ctx->status_mutex); ctx->mapping = mapping; mutex_init(&ctx->mapping_lock); @@ -47,6 +48,59 @@ int ocxl_context_alloc(struct ocxl_context **context, struct ocxl_afu *afu, } EXPORT_SYMBOL_GPL(ocxl_context_alloc);

+/** + * ocxl_context_get() - Get a reference to the context if not closed + * @ctx: The context + * + * Atomically checks if context status is not CLOSED and acquires a reference. + * Must be called with ctx->status_mutex held. + * + * Return: true if reference acquired, false if context is CLOSED + */ +bool ocxl_context_get(struct ocxl_context *ctx) +{ + lockdep_assert_held(&ctx->status_mutex); + + if (ctx->status == CLOSED) + return false; + + kref_get(&ctx->kref); + return true; +} +EXPORT_SYMBOL_GPL(ocxl_context_get); + +/* + * kref release callback - called when last reference is dropped + */ +static void ocxl_context_release(struct kref *kref) +{ + struct ocxl_context *ctx = container_of(kref, struct ocxl_context, + kref); + + mutex_lock(&ctx->afu->contexts_lock); + ctx->afu->pasid_count--; + idr_remove(&ctx->afu->contexts_idr, ctx->pasid); + mutex_unlock(&ctx->afu->contexts_lock); + + ocxl_afu_irq_free_all(ctx); + idr_destroy(&ctx->irq_idr); + /* reference to the AFU taken in ocxl_context_alloc() */ + ocxl_afu_put(ctx->afu); + kfree(ctx); +} + +/** + * ocxl_context_put() - Release a reference to the context + * @ctx: The context + * + * Decrements the reference count. When it reaches zero, the context is freed. + */ +void ocxl_context_put(struct ocxl_context *ctx) +{ + kref_put(&ctx->kref, ocxl_context_release); +} +EXPORT_SYMBOL_GPL(ocxl_context_put); + /* * Callback for when a translation fault triggers an error * data: a pointer to the context which triggered the fault @@ -279,18 +333,3 @@ void ocxl_context_detach_all(struct ocxl_afu *afu) } mutex_unlock(&afu->contexts_lock); } - -void ocxl_context_free(struct ocxl_context *ctx) -{ - mutex_lock(&ctx->afu->contexts_lock); - ctx->afu->pasid_count--; - idr_remove(&ctx->afu->contexts_idr, ctx->pasid); - mutex_unlock(&ctx->afu->contexts_lock); - - ocxl_afu_irq_free_all(ctx); - idr_destroy(&ctx->irq_idr); - /* reference to the AFU taken in ocxl_context_alloc() */ - ocxl_afu_put(ctx->afu); - kfree(ctx); -} -EXPORT_SYMBOL_GPL(ocxl_context_free); diff --git a/drivers/misc/ocxl/file.c b/drivers/misc/ocxl/file.c index 7eb74711ac96..c08724e7ff1e 100644 --- a/drivers/misc/ocxl/file.c +++ b/drivers/misc/ocxl/file.c @@ -204,17 +204,21 @@ static long afu_ioctl(struct file *file, unsigned int cmd, int irq_id; u64 irq_offset; long rc; - bool closed; - - pr_debug("%s for context %d, command %s\n", __func__, ctx->pasid, - CMD_STR(cmd));

+ /* + * Hold a reference to the context for the duration of this operation. + * We check the status and acquire the reference atomically under the + * status_mutex to ensure the context remains valid. + */ mutex_lock(&ctx->status_mutex); - closed = (ctx->status == CLOSED); + if (!ocxl_context_get(ctx)) { + mutex_unlock(&ctx->status_mutex); + return -EIO; + } mutex_unlock(&ctx->status_mutex);

- if (closed) - return -EIO; + pr_debug("%s for context %d, command %s\n", __func__, ctx->pasid, + CMD_STR(cmd));

switch (cmd) { case OCXL_IOCTL_ATTACH: @@ -230,7 +234,7 @@ static long afu_ioctl(struct file *file, unsigned int cmd, sizeof(irq_offset)); if (rc) { ocxl_afu_irq_free(ctx, irq_id); - return -EFAULT; + rc = -EFAULT; } } break; @@ -238,8 +242,10 @@ static long afu_ioctl(struct file *file, unsigned int cmd, case OCXL_IOCTL_IRQ_FREE: rc = copy_from_user(&irq_offset, (u64 __user *) args, sizeof(irq_offset)); - if (rc) - return -EFAULT; + if (rc) { + rc = -EFAULT; + break; + } irq_id = ocxl_irq_offset_to_id(ctx, irq_offset); rc = ocxl_afu_irq_free(ctx, irq_id); break; @@ -247,14 +253,20 @@ static long afu_ioctl(struct file *file, unsigned int cmd, case OCXL_IOCTL_IRQ_SET_FD: rc = copy_from_user(&irq_fd, (u64 __user *) args, sizeof(irq_fd)); - if (rc) - return -EFAULT; - if (irq_fd.reserved) - return -EINVAL; + if (rc) { + rc = -EFAULT; + break; + } + if (irq_fd.reserved) { + rc = -EINVAL; + break; + } irq_id = ocxl_irq_offset_to_id(ctx, irq_fd.irq_offset); ev_ctx = eventfd_ctx_fdget(irq_fd.eventfd); - if (IS_ERR(ev_ctx)) - return PTR_ERR(ev_ctx); + if (IS_ERR(ev_ctx)) { + rc = PTR_ERR(ev_ctx); + break; + } rc = ocxl_irq_set_handler(ctx, irq_id, irq_handler, irq_free, ev_ctx); if (rc) eventfd_ctx_put(ev_ctx); @@ -280,6 +292,8 @@ static long afu_ioctl(struct file *file, unsigned int cmd, default: rc = -EINVAL; } + + ocxl_context_put(ctx); return rc; }

@@ -292,9 +306,23 @@ static long afu_compat_ioctl(struct file *file, unsigned int cmd, static int afu_mmap(struct file *file, struct vm_area_struct *vma) { struct ocxl_context *ctx = file->private_data; + int rc; + + /* + * Hold a reference during mmap setup to ensure the context + * remains valid. + */ + mutex_lock(&ctx->status_mutex); + if (!ocxl_context_get(ctx)) { + mutex_unlock(&ctx->status_mutex); + return -EIO; + } + mutex_unlock(&ctx->status_mutex);

pr_debug("%s for context %d\n", __func__, ctx->pasid); - return ocxl_context_mmap(ctx, vma); + rc = ocxl_context_mmap(ctx, vma); + ocxl_context_put(ctx); + return rc; }

static bool has_xsl_error(struct ocxl_context *ctx) @@ -324,21 +352,31 @@ static unsigned int afu_poll(struct file *file, struct poll_table_struct *wait) { struct ocxl_context *ctx = file->private_data; unsigned int mask = 0; - bool closed; + + /* + * Hold a reference to the context while checking for events. + */ + mutex_lock(&ctx->status_mutex); + if (!ocxl_context_get(ctx)) { + mutex_unlock(&ctx->status_mutex); + return EPOLLERR; + } + mutex_unlock(&ctx->status_mutex);

pr_debug("%s for context %d\n", __func__, ctx->pasid);

poll_wait(file, &ctx->events_wq, wait);

- mutex_lock(&ctx->status_mutex); - closed = (ctx->status == CLOSED); - mutex_unlock(&ctx->status_mutex); - if (afu_events_pending(ctx)) mask = EPOLLIN | EPOLLRDNORM; - else if (closed) - mask = EPOLLERR; + else { + mutex_lock(&ctx->status_mutex); + if (ctx->status == CLOSED) + mask = EPOLLERR; + mutex_unlock(&ctx->status_mutex); + }

+ ocxl_context_put(ctx); return mask; }

@@ -410,6 +448,16 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count, AFU_EVENT_BODY_MAX_SIZE)) return -EINVAL;

+ /* + * Hold a reference to the context for the duration of the read operation. + */ + mutex_lock(&ctx->status_mutex); + if (!ocxl_context_get(ctx)) { + mutex_unlock(&ctx->status_mutex); + return -EIO; + } + mutex_unlock(&ctx->status_mutex); + for (;;) { prepare_to_wait(&ctx->events_wq, &event_wait, TASK_INTERRUPTIBLE); @@ -422,11 +470,13 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,

if (file->f_flags & O_NONBLOCK) { finish_wait(&ctx->events_wq, &event_wait); + ocxl_context_put(ctx); return -EAGAIN; }

if (signal_pending(current)) { finish_wait(&ctx->events_wq, &event_wait); + ocxl_context_put(ctx); return -ERESTARTSYS; }

@@ -437,19 +487,24 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,

if (has_xsl_error(ctx)) { used = append_xsl_error(ctx, &header, buf + sizeof(header)); - if (used < 0) + if (used < 0) { + ocxl_context_put(ctx); return used; + } }

if (!afu_events_pending(ctx)) header.flags |= OCXL_KERNEL_EVENT_FLAG_LAST;

- if (copy_to_user(buf, &header, sizeof(header))) + if (copy_to_user(buf, &header, sizeof(header))) { + ocxl_context_put(ctx); return -EFAULT; + }

used += sizeof(header);

rc = used; + ocxl_context_put(ctx); return rc; }

@@ -464,8 +519,12 @@ static int afu_release(struct inode *inode, struct file *file) ctx->mapping = NULL; mutex_unlock(&ctx->mapping_lock); wake_up_all(&ctx->events_wq); + /* + * Drop the initial reference from afu_open(). The context will be + * freed when all references are released. + */ if (rc != -EBUSY) - ocxl_context_free(ctx); + ocxl_context_put(ctx); return 0; }

diff --git a/drivers/misc/ocxl/ocxl_internal.h b/drivers/misc/ocxl/ocxl_internal.h index d2028d6c6f08..6eab7806b43d 100644 --- a/drivers/misc/ocxl/ocxl_internal.h +++ b/drivers/misc/ocxl/ocxl_internal.h @@ -5,6 +5,7 @@

#include <linux/pci.h> #include <linux/cdev.h> +#include <linux/kref.h> #include <linux/list.h> #include <misc/ocxl.h>

@@ -68,6 +69,7 @@ struct ocxl_xsl_error { };

struct ocxl_context { + struct kref kref; struct ocxl_afu *afu; int pasid; struct mutex status_mutex; @@ -140,6 +142,8 @@ int ocxl_link_update_pe(void *link_handle, int pasid, __u16 tid);

int ocxl_context_mmap(struct ocxl_context *ctx, struct vm_area_struct *vma); +bool ocxl_context_get(struct ocxl_context *ctx); +void ocxl_context_put(struct ocxl_context *ctx); void ocxl_context_detach_all(struct ocxl_afu *afu);

int ocxl_sysfs_register_afu(struct ocxl_file_info *info);