From: Rasmus Villemoes linux@rasmusvillemoes.dk
[ Upstream commit b234ed6d629420827e2839c8c8935be85a0867fd ]
Currently, usermodehelper is enabled right before PID1 starts going through the initcalls. However, any call of a usermodehelper from a pure_, core_, postcore_, arch_, subsys_ or fs_ initcall is futile, as there is no filesystem contents yet.
Up until commit e7cb072eb988 ("init/initramfs.c: do unpacking asynchronously"), such calls, whether via some request_module(), a legacy uevent "/sbin/hotplug" notification or something else, would just fail silently with (presumably) -ENOENT from kernel_execve(). However, that commit introduced the wait_for_initramfs() synchronization hook which must be called from the usermodehelper exec path right before the kernel_execve, in order that request_module() et al done from *after* rootfs_initcall() time (i.e. device_ and late_ initcalls) would continue to find a populated initramfs as they used to.
Any call of wait_for_initramfs() done before the unpacking has been scheduled (i.e. before rootfs_initcall time) must just return immediately [and let the caller find an empty file system] in order not to deadlock the machine. I mistakenly thought, and my limited testing confirmed, that there were no such calls, so I added a pr_warn_once() in wait_for_initramfs(). It turns out that one can indeed hit request_module() as well as kobject_uevent_env() during those early init calls, leading to a user-visible warning in the kernel log emitted consistently for certain configurations.
We could just remove the pr_warn_once(), but I think it's better to postpone enabling the usermodehelper framework until there is at least some chance of finding the executable. That is also a little more efficient in that a lot of work done in umh.c will be elided. However, it does change the error seen by those early callers from -ENOENT to -EBUSY, so there is a risk of a regression if any caller care about the exact error value.
Link: https://lkml.kernel.org/r/20210728134638.329060-1-linux@rasmusvillemoes.dk Fixes: e7cb072eb988 ("init/initramfs.c: do unpacking asynchronously") Signed-off-by: Rasmus Villemoes linux@rasmusvillemoes.dk Reported-by: Alexander Egorenkov egorenar@linux.ibm.com Reported-by: Bruno Goncalves bgoncalv@redhat.com Reported-by: Heiner Kallweit hkallweit1@gmail.com Cc: Luis Chamberlain mcgrof@kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- init/initramfs.c | 2 ++ init/main.c | 1 - init/noinitramfs.c | 2 ++ 3 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/init/initramfs.c b/init/initramfs.c index af27abc59643..a842c0544745 100644 --- a/init/initramfs.c +++ b/init/initramfs.c @@ -15,6 +15,7 @@ #include <linux/mm.h> #include <linux/namei.h> #include <linux/init_syscalls.h> +#include <linux/umh.h>
static ssize_t __init xwrite(struct file *file, const char *p, size_t count, loff_t *pos) @@ -727,6 +728,7 @@ static int __init populate_rootfs(void) { initramfs_cookie = async_schedule_domain(do_populate_rootfs, NULL, &initramfs_domain); + usermodehelper_enable(); if (!initramfs_async) wait_for_initramfs(); return 0; diff --git a/init/main.c b/init/main.c index 8d97aba78c3a..90733a916791 100644 --- a/init/main.c +++ b/init/main.c @@ -1392,7 +1392,6 @@ static void __init do_basic_setup(void) driver_init(); init_irq_proc(); do_ctors(); - usermodehelper_enable(); do_initcalls(); }
diff --git a/init/noinitramfs.c b/init/noinitramfs.c index 3d62b07f3bb9..d1d26b93d25c 100644 --- a/init/noinitramfs.c +++ b/init/noinitramfs.c @@ -10,6 +10,7 @@ #include <linux/kdev_t.h> #include <linux/syscalls.h> #include <linux/init_syscalls.h> +#include <linux/umh.h>
/* * Create a simple rootfs that is similar to the default initramfs @@ -18,6 +19,7 @@ static int __init default_rootfs(void) { int err;
+ usermodehelper_enable(); err = init_mkdir("/dev", 0755); if (err < 0) goto out;