[PATCH 5.10 137/575] ovl: fix use after free in struct ovl_aio_req
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2021-11-15 19:27:29
Also in:
lkml
From: yangerkun <redacted>
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 <redacted>
Link: https://lore.kernel.org/r/20210930032228.3199690-3-yangerkun@huawei.com/ (local)
Cc: <redacted> # v5.6
Signed-off-by: Miklos Szeredi <redacted>
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; };
@@ -257,6 +258,14 @@ 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;
@@ -273,8 +282,7 @@ 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)
@@ -324,7 +332,9 @@ 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); }
@@ -395,7 +405,9 @@ 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); }