[PATCH 6.18 44/49] erofs: fix UAF issue for file-backed mounts w/ directio option

Greg Kroah-Hartman
2026-02-13T13:54:11Z

From: Chao Yu <chao@kernel.org>

commit 1caf50ce4af096d0280d59a31abdd85703cd995c upstream.

[ 9.269940][ T3222] Call trace:
[ 9.269948][ T3222] ext4_file_read_iter+0xac/0x108
[ 9.269979][ T3222] vfs_iocb_iter_read+0xac/0x198
[ 9.269993][ T3222] erofs_fileio_rq_submit+0x12c/0x180
[ 9.270008][ T3222] erofs_fileio_submit_bio+0x14/0x24
[ 9.270030][ T3222] z_erofs_runqueue+0x834/0x8ac
[ 9.270054][ T3222] z_erofs_read_folio+0x120/0x220
[ 9.270083][ T3222] filemap_read_folio+0x60/0x120
[ 9.270102][ T3222] filemap_fault+0xcac/0x1060
[ 9.270119][ T3222] do_pte_missing+0x2d8/0x1554
[ 9.270131][ T3222] handle_mm_fault+0x5ec/0x70c
[ 9.270142][ T3222] do_page_fault+0x178/0x88c
[ 9.270167][ T3222] do_translation_fault+0x38/0x54
[ 9.270183][ T3222] do_mem_abort+0x54/0xac
[ 9.270208][ T3222] el0_da+0x44/0x7c
[ 9.270227][ T3222] el0t_64_sync_handler+0x5c/0xf4
[ 9.270253][ T3222] el0t_64_sync+0x1bc/0x1c0

EROFS may encounter above panic when enabling file-backed mount w/
directio mount option, the root cause is it may suffer UAF in below
race condition:

- z_erofs_read_folio wq s_dio_done_wq
- z_erofs_runqueue
- erofs_fileio_submit_bio
- erofs_fileio_rq_submit
- vfs_iocb_iter_read
- ext4_file_read_iter
- ext4_dio_read_iter
- iomap_dio_rw
: bio was submitted and return -EIOCBQUEUED
- dio_aio_complete_work
- dio_complete
- dio->iocb->ki_complete (erofs_fileio_ki_complete())
- kfree(rq)
: it frees iocb, iocb.ki_filp can be UAF in file_accessed().
- file_accessed
: access NULL file point

Introduce a reference count in struct erofs_fileio_rq, and initialize it
as two, both erofs_fileio_ki_complete() and erofs_fileio_rq_submit() will
decrease reference count, the last one decreasing the reference count
to zero will free rq.

Cc: stable@kernel.org
Fixes: fb176750266a ("erofs: add file-backed mount support")
Fixes: 6422cde1b0d5 ("erofs: use buffered I/O for file-backed mounts by default")
Signed-off-by: Chao Yu <chao@kernel.org>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/erofs/fileio.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/fs/erofs/fileio.c
+++ b/fs/erofs/fileio.c
@@ -10,6 +10,7 @@ struct erofs_fileio_rq {
struct bio bio;
struct kiocb iocb;
struct super_block *sb;
+ refcount_t ref;
};

struct erofs_fileio {
@@ -42,7 +43,8 @@ static void erofs_fileio_ki_complete(str
}
}
bio_uninit(&rq->bio);
- kfree(rq);
+ if (refcount_dec_and_test(&rq->ref))
+ kfree(rq);
}

static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq)
@@ -66,6 +68,8 @@ static void erofs_fileio_rq_submit(struc
revert_creds(old_cred);
if (ret != -EIOCBQUEUED)
erofs_fileio_ki_complete(&rq->iocb, ret);
+ if (refcount_dec_and_test(&rq->ref))
+ kfree(rq);
}

static struct erofs_fileio_rq *erofs_fileio_rq_alloc(struct erofs_map_dev *mdev)
@@ -76,6 +80,7 @@ static struct erofs_fileio_rq *erofs_fil
bio_init(&rq->bio, NULL, rq->bvecs, ARRAY_SIZE(rq->bvecs), REQ_OP_READ);
rq->iocb.ki_filp = mdev->m_dif->file;
rq->sb = mdev->m_sb;
+ refcount_set(&rq->ref, 2);
return rq;
}