From: Chao Yu Date: Thu, 5 Feb 2026 22:30:05 +0000 (+0800) Subject: erofs: fix UAF issue for file-backed mounts w/ directio option X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1caf50ce4af096d0280d59a31abdd85703cd995c;p=thirdparty%2Flinux.git erofs: fix UAF issue for file-backed mounts w/ directio option [ 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 Reviewed-by: Gao Xiang Signed-off-by: Gao Xiang --- diff --git a/fs/erofs/fileio.c b/fs/erofs/fileio.c index 43998fe1cce1d..4d5054dcac95a 100644 --- 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 { @@ -38,7 +39,8 @@ static void erofs_fileio_ki_complete(struct kiocb *iocb, long ret) } bio_endio(&rq->bio); 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) @@ -60,6 +62,8 @@ static void erofs_fileio_rq_submit(struct erofs_fileio_rq *rq) ret = vfs_iocb_iter_read(rq->iocb.ki_filp, &rq->iocb, &iter); 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) @@ -70,6 +74,7 @@ static struct erofs_fileio_rq *erofs_fileio_rq_alloc(struct erofs_map_dev *mdev) 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; }