From bdf99135d3c87fb94f6cb8ff54d29037efbd04de Mon Sep 17 00:00:00 2001 From: Tong Zhang Date: Sat, 29 Jan 2022 13:40:55 -0800 Subject: [PATCH] binfmt_misc: fix crash when load/unload module We should unregister the table upon module unload otherwise something horrible will happen when we load binfmt_misc module again. Also note that we should keep value returned by register_sysctl_mount_point() and release it later, otherwise it will leak. Also, per Christian's comment, to fully restore the old behavior that won't break userspace the check(binfmt_misc_header) should be eliminated. To reproduce: modprobe binfmt_misc modprobe -r binfmt_misc modprobe binfmt_misc modprobe -r binfmt_misc modprobe binfmt_misc resulting in modprobe: can't load module binfmt_misc (kernel/fs/binfmt_misc.ko): Cannot allocate memory and an unhappy kernel: binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point BUG: unable to handle page fault for address: fffffbfff8004802 Call Trace: init_misc_binfmt+0x2d/0x1000 [binfmt_misc] Link: https://lkml.kernel.org/r/20220124181812.1869535-2-ztong0001@gmail.com Fixes: 79fbc4829c8b ("fs: move binfmt_misc sysctl to its own file") Signed-off-by: Tong Zhang Co-developed-by: Christian Brauner Acked-by: Luis Chamberlain Cc: Eric Biederman Cc: Kees Cook Cc: Iurii Zaikin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/binfmt_misc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index ddea6acbddde5..c07f35719ee3f 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -817,20 +817,20 @@ static struct file_system_type bm_fs_type = { }; MODULE_ALIAS_FS("binfmt_misc"); +static struct ctl_table_header *binfmt_misc_header; + static int __init init_misc_binfmt(void) { int err = register_filesystem(&bm_fs_type); if (!err) insert_binfmt(&misc_format); - if (!register_sysctl_mount_point("fs/binfmt_misc")) { - pr_warn("Failed to create fs/binfmt_misc sysctl mount point"); - return -ENOMEM; - } + binfmt_misc_header = register_sysctl_mount_point("fs/binfmt_misc"); return 0; } static void __exit exit_misc_binfmt(void) { + unregister_sysctl_table(binfmt_misc_header); unregister_binfmt(&misc_format); unregister_filesystem(&bm_fs_type); } -- 2.39.5