The patch titled
Subject: binfmt_misc: fix crash when load/unload module
has been added to the -mm tree. Its filename is
binfmt_misc-fix-crash-when-load-unload-module.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/binfmt_misc-fix-crash-when-load-unload-module.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/binfmt_misc-fix-crash-when-load-unload-module.patch
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------------------------------------------------------
From: Tong Zhang <ztong0001@xxxxxxxxx>
Subject: 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.
reproduce:
modprobe binfmt_misc
modprobe -r binfmt_misc
modprobe binfmt_misc
modprobe -r binfmt_misc
modprobe binfmt_misc
[ 18.032038] Call Trace:
[ 18.032108] <TASK>
[ 18.032169] dump_stack_lvl+0x34/0x44
[ 18.032273] __register_sysctl_table+0x6f4/0x720
[ 18.032397] ? preempt_count_sub+0xf/0xb0
[ 18.032508] ? 0xffffffffc0040000
[ 18.032600] init_misc_binfmt+0x2d/0x1000 [binfmt_misc]
[ 18.042520] binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point
modprobe: can't load module binfmt_misc (kernel/fs/binfmt_misc.ko): Cannot allocate memory
[ 18.063549] binfmt_misc: Failed to create fs/binfmt_misc sysctl mount point
[ 18.204779] BUG: unable to handle page fault for address: fffffbfff8004802
Link: https://lkml.kernel.org/r/20220124181812.1869535-2-ztong0001@xxxxxxxxx
Fixes: 3ba442d5331f ("fs: move binfmt_misc sysctl to its own file")
Signed-off-by: Tong Zhang <ztong0001@xxxxxxxxx>
Co-developed-by: Christian Brauner<brauner@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Iurii Zaikin <yzaikin@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/binfmt_misc.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/fs/binfmt_misc.c~binfmt_misc-fix-crash-when-load-unload-module
+++ a/fs/binfmt_misc.c
@@ -817,20 +817,20 @@ static struct file_system_type bm_fs_typ
};
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);
}
_
Patches currently in -mm which might be from ztong0001@xxxxxxxxx are
binfmt_misc-fix-crash-when-load-unload-module.patch
