From: Gao Xiang Date: Fri, 22 May 2026 08:27:16 +0000 (+0800) Subject: erofs: fix use-after-free on sbi->sync_decompress X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=1aee05e814d292064bf5fa15733741040cdc48ba;p=thirdparty%2Flinux.git erofs: fix use-after-free on sbi->sync_decompress z_erofs_decompress_kickoff() can race with filesystem unmount, causing a use-after-free on sbi->sync_decompress. When I/O completes, z_erofs_endio() calls z_erofs_decompress_kickoff() to queue z_erofs_decompressqueue_work() asynchronously. Then, after all folios are unlocked, unmount workflow can proceed and sbi will be freed before accessing to sbi->sync_decompress. Thread (unmount) I/O completion kworker queue_work z_erofs_decompressqueue_work (all folios are unlocked) cleanup_mnt .. erofs_kill_sb erofs_sb_free kfree(sbi) access sbi->sync_decompress // UAF!! Fixes: 40452ffca3c1 ("erofs: add sysfs node to control sync decompression strategy") Reported-by: syzbot+52bae5c495dbe261a0bc@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=52bae5c495dbe261a0bc Reviewed-by: Chao Yu Reviewed-by: Jianan Huang Signed-off-by: Gao Xiang --- diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c index 27ab7bd844ec7..c6240dccbb0f0 100644 --- a/fs/erofs/zdata.c +++ b/fs/erofs/zdata.c @@ -1455,6 +1455,9 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io, if (atomic_add_return(bios, &io->pending_bios)) return; if (z_erofs_in_atomic()) { + /* See `sync_decompress` in sysfs-fs-erofs for more details */ + if (sbi->sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO) + sbi->sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON; #ifdef CONFIG_EROFS_FS_PCPU_KTHREAD struct kthread_worker *worker; @@ -1471,9 +1474,6 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io, #else queue_work(z_erofs_workqueue, &io->u.work); #endif - /* See `sync_decompress` in sysfs-fs-erofs for more details */ - if (sbi->sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO) - sbi->sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON; return; } gfp_flag = memalloc_noio_save();