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aio: fix use-after-free in aio_migratepage

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Dmitry Vyukov managed to trigger a case where aio_migratepage can cause a
use-after-free during teardown of the aio ring buffer's mapping.  This turns
out to be caused by access to the ioctx's ring_pages via the migratepage
operation which was not being protected by any locks during ioctx freeing.
Use the address_space's private_lock to protect use and updates of the mapping's
private_data, and make ioctx teardown unlink the ioctx from the address space.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
This commit is contained in:
Benjamin LaHaise 2013-09-26 20:34:51 -04:00
parent 4b97280675
commit 5e9ae2e5da
1 changed files with 37 additions and 15 deletions
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52
fs/aio.c
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@ -167,10 +167,25 @@ static int __init aio_setup(void)
}
__initcall(aio_setup);
static void put_aio_ring_file(struct kioctx *ctx)
{
struct file *aio_ring_file = ctx->aio_ring_file;
if (aio_ring_file) {
truncate_setsize(aio_ring_file->f_inode, 0);
/* Prevent further access to the kioctx from migratepages */
spin_lock(&aio_ring_file->f_inode->i_mapping->private_lock);
aio_ring_file->f_inode->i_mapping->private_data = NULL;
ctx->aio_ring_file = NULL;
spin_unlock(&aio_ring_file->f_inode->i_mapping->private_lock);
fput(aio_ring_file);
}
}
static void aio_free_ring(struct kioctx *ctx)
{
int i;
struct file *aio_ring_file = ctx->aio_ring_file;
for (i = 0; i < ctx->nr_pages; i++) {
pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
@ -178,14 +193,10 @@ static void aio_free_ring(struct kioctx *ctx)
put_page(ctx->ring_pages[i]);
}
put_aio_ring_file(ctx);
if (ctx->ring_pages && ctx->ring_pages != ctx->internal_pages)
kfree(ctx->ring_pages);
if (aio_ring_file) {
truncate_setsize(aio_ring_file->f_inode, 0);
fput(aio_ring_file);
ctx->aio_ring_file = NULL;
}
}
static int aio_ring_mmap(struct file *file, struct vm_area_struct *vma)
@ -207,9 +218,8 @@ static int aio_set_page_dirty(struct page *page)
static int aio_migratepage(struct address_space *mapping, struct page *new,
struct page *old, enum migrate_mode mode)
{
struct kioctx *ctx = mapping->private_data;
struct kioctx *ctx;
unsigned long flags;
unsigned idx = old->index;
int rc;
/* Writeback must be complete */
@ -224,10 +234,23 @@ static int aio_migratepage(struct address_space *mapping, struct page *new,
get_page(new);
spin_lock_irqsave(&ctx->completion_lock, flags);
migrate_page_copy(new, old);
ctx->ring_pages[idx] = new;
spin_unlock_irqrestore(&ctx->completion_lock, flags);
/* We can potentially race against kioctx teardown here. Use the
* address_space's private data lock to protect the mapping's
* private_data.
*/
spin_lock(&mapping->private_lock);
ctx = mapping->private_data;
if (ctx) {
pgoff_t idx;
spin_lock_irqsave(&ctx->completion_lock, flags);
migrate_page_copy(new, old);
idx = old->index;
if (idx < (pgoff_t)ctx->nr_pages)
ctx->ring_pages[idx] = new;
spin_unlock_irqrestore(&ctx->completion_lock, flags);
} else
rc = -EBUSY;
spin_unlock(&mapping->private_lock);
return rc;
}
@ -617,8 +640,7 @@ out_freepcpu:
out_freeref:
free_percpu(ctx->users.pcpu_count);
out_freectx:
if (ctx->aio_ring_file)
fput(ctx->aio_ring_file);
put_aio_ring_file(ctx);
kmem_cache_free(kioctx_cachep, ctx);
pr_debug("error allocating ioctx %d\n", err);
return ERR_PTR(err);