[PATCH 5.15 138/917] ovl: fix use after free in struct ovl_aio_req

Greg Kroah-Hartman
2021-11-16T01:07:16Z

From: yangerkun <yangerkun@huawei.com>

commit 9a254403760041528bc8f69fe2f5e1ef86950991 upstream.

Example for triggering use after free in a overlay on ext4 setup:

aio_read
ovl_read_iter
vfs_iter_read
ext4_file_read_iter
ext4_dio_read_iter
iomap_dio_rw -> -EIOCBQUEUED
/*
* Here IO is completed in a separate thread,
* ovl_aio_cleanup_handler() frees aio_req which has iocb embedded
*/
file_accessed(iocb->ki_filp); /**BOOM**/

Fix by introducing a refcount in ovl_aio_req similarly to aio_kiocb. This
guarantees that iocb is only freed after vfs_read/write_iter() returns on
underlying fs.

Fixes: 2406a307ac7d ("ovl: implement async IO routines")
Signed-off-by: yangerkun <yangerkun@huawei.com>
Link: https://lore.kernel.org/r/20210930032228.3199690-3-yangerkun@huawei.com/
Cc: <stable@vger.kernel.org> # v5.6
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/overlayfs/file.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -17,6 +17,7 @@

struct ovl_aio_req {
struct kiocb iocb;
+ refcount_t ref;
struct kiocb *orig_iocb;
struct fd fd;
};
@@ -252,6 +253,14 @@ static rwf_t ovl_iocb_to_rwf(int ifl)
return flags;
}

+static inline void ovl_aio_put(struct ovl_aio_req *aio_req)
+{
+ if (refcount_dec_and_test(&aio_req->ref)) {
+ fdput(aio_req->fd);
+ kmem_cache_free(ovl_aio_request_cachep, aio_req);
+ }
+}
+
static void ovl_aio_cleanup_handler(struct ovl_aio_req *aio_req)
{
struct kiocb *iocb = &aio_req->iocb;
@@ -268,8 +277,7 @@ static void ovl_aio_cleanup_handler(stru
}

orig_iocb->ki_pos = iocb->ki_pos;
- fdput(aio_req->fd);
- kmem_cache_free(ovl_aio_request_cachep, aio_req);
+ ovl_aio_put(aio_req);
}

static void ovl_aio_rw_complete(struct kiocb *iocb, long res, long res2)
@@ -319,7 +327,9 @@ static ssize_t ovl_read_iter(struct kioc
aio_req->orig_iocb = iocb;
kiocb_clone(&aio_req->iocb, iocb, real.file);
aio_req->iocb.ki_complete = ovl_aio_rw_complete;
+ refcount_set(&aio_req->ref, 2);
ret = vfs_iocb_iter_read(real.file, &aio_req->iocb, iter);
+ ovl_aio_put(aio_req);
if (ret != -EIOCBQUEUED)
ovl_aio_cleanup_handler(aio_req);
}
@@ -390,7 +400,9 @@ static ssize_t ovl_write_iter(struct kio
kiocb_clone(&aio_req->iocb, iocb, real.file);
aio_req->iocb.ki_flags = ifl;
aio_req->iocb.ki_complete = ovl_aio_rw_complete;
+ refcount_set(&aio_req->ref, 2);
ret = vfs_iocb_iter_write(real.file, &aio_req->iocb, iter);
+ ovl_aio_put(aio_req);
if (ret != -EIOCBQUEUED)
ovl_aio_cleanup_handler(aio_req);
}