Re: [LKP] [mtd] c4dfa25ab3: kernel_BUG_at_fs/sysfs/file.c

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Jan 02, 2019 at 10:44:50PM +0100, Rafael J. Wysocki wrote:
> On Wed, Jan 2, 2019 at 8:53 PM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> 
> [cut]
> 
> > Greg, Rafael: it does strike me that the "BUG_ON()" in
> > sysfs_create_file_ns() could easily have been a
> >
> >         if (WARN_ON(..))
> >                 return -EINVAL;
> >
> > which would have made the machine boot and probably make things easier
> > for normal users to report. The kernel test robot doesn't care, but
> > non-booting kernels are usually not nice to debug or report for normal
> > human beings..
> 
> I agree.
> 
> This isn't a good enough reason to crash the kernel IMO.

I agree too.

Here's a patch for this, I'll queue it up after -rc1 is out.  Rafael,
look good to you?

--------------

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: [PATCH] sysfs: convert BUG_ON to WARN_ON

It's rude to crash the system just because the developer did something
wrong, as it prevents them from usually even seeing what went wrong.

So convert the few BUG_ON() calls that have snuck into the sysfs code
over the years to WARN_ON() to make it more "friendly".  All of these
are able to be recovered from, so it makes no sense to crash.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/sysfs/dir.c     | 3 ++-
 fs/sysfs/file.c    | 6 ++++--
 fs/sysfs/group.c   | 3 ++-
 fs/sysfs/symlink.c | 3 ++-
 4 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index feeae8081c22..aa85f2874a9f 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -43,7 +43,8 @@ int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
 	kuid_t uid;
 	kgid_t gid;
 
-	BUG_ON(!kobj);
+	if (WARN_ON(!kobj))
+		return -EINVAL;
 
 	if (kobj->parent)
 		parent = kobj->parent->sd;
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index bb71db63c99c..51398457fe00 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -325,7 +325,8 @@ int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
 	kuid_t uid;
 	kgid_t gid;
 
-	BUG_ON(!kobj || !kobj->sd || !attr);
+	if (WARN_ON(!kobj || !kobj->sd || !attr))
+		return -EINVAL;
 
 	kobject_get_ownership(kobj, &uid, &gid);
 	return sysfs_add_file_mode_ns(kobj->sd, attr, false, attr->mode,
@@ -537,7 +538,8 @@ int sysfs_create_bin_file(struct kobject *kobj,
 	kuid_t uid;
 	kgid_t gid;
 
-	BUG_ON(!kobj || !kobj->sd || !attr);
+	if (WARN_ON(!kobj || !kobj->sd || !attr))
+		return -EINVAL;
 
 	kobject_get_ownership(kobj, &uid, &gid);
 	return sysfs_add_file_mode_ns(kobj->sd, &attr->attr, true,
diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 1eb2d6307663..57038604d4a8 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -112,7 +112,8 @@ static int internal_create_group(struct kobject *kobj, int update,
 	kgid_t gid;
 	int error;
 
-	BUG_ON(!kobj || (!update && !kobj->sd));
+	if (WARN_ON(!kobj || (!update && !kobj->sd)))
+		return -EINVAL;
 
 	/* Updates may happen before the object has been instantiated */
 	if (unlikely(update && !kobj->sd))
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 215c225b2ca1..c4deecc80f67 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -23,7 +23,8 @@ static int sysfs_do_create_link_sd(struct kernfs_node *parent,
 {
 	struct kernfs_node *kn, *target = NULL;
 
-	BUG_ON(!name || !parent);
+	if (WARN_ON(!name || !parent))
+		return -EINVAL;
 
 	/*
 	 * We don't own @target_kobj and it may be removed at any time.
-- 
2.20.1