[PATCH v3 0/2] PM / Hibernate: sysfs resume

[PATCH v3 0/2] PM / Hibernate: sysfs resume

[Sebastian Capella]

Patchsets related to hibernation resume:
  - enhancement to make the use of an existing resume file more general
  - enhance name_to_dev_t to ignore trailing newlines coming from userspace.

Both patches are based on the 3.12-rc3 tag.  This was tested on a
Pandaboard with partial hibernation support, and compiled for x86.

[PATCH 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t
  init/do_mounts.c |   23 ++++++++++++++++++-----
  1 file changed, 18 insertions(+), 5 deletions(-)

  Changes name_to_dev_t to handle a trailing newline in the
  input buffer, which will allow name_to_dev_t to be used
  directly with user buffers without requiring a copy.
  Also adds a const to the name parameter which reflects
  how name_to_dev_t is treating the input buffer currently.
  This also allows direct use of user buffers
  (from resume_store for example).

[PATCH 2/2] PM / Hibernate: use name_to_dev_t to parse resume
  kernel/power/hibernate.c |   15 ++++-----------
  1 file changed, 4 insertions(+), 11 deletions(-)

  Use name_to_dev_t to parse the /sys/power/resume file making the
  syntax more flexible.  It supports the previous use syntax
  and additionally can support other formats such as
  /dev/devicenode and UUID= formats.

  By changing /sys/debug/resume to accept the same syntax as
  the resume=device parameter, we can parse the resume=device
  in the initrd init script and use the resume device directly
  from the kernel command line.

Changes in v3:
--------------
* Dropped documentation patch as it went in through trivial
* Added patch for name_to_dev_t to support directly parsing userspace
  buffer

Changes in v2:
--------------
* Added check for null return of kstrndup in hibernate.c

Thanks,

Sebastian

[PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t

[Sebastian Capella]

Enhance name_to_dev_t to handle trailing newline characters
on device paths.  Some inputs to name_to_dev_t may come from
userspace where oftentimes a '\n' is appended to the path.
Added const to the name buffer in both the function
declaration and the prototype to reflect input buffer
handling.

By handling trailing newlines in name_to_dev_t, userspace
buffers may be directly passed to name_to_dev_t without
modification.

Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Stephen Warren <swarren@nvidia.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
---
 include/linux/mount.h |    2 +-
 init/do_mounts.c      |   25 +++++++++++++++++++------
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/linux/mount.h b/include/linux/mount.h
index 38cd98f..fdbb3e6 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -77,6 +77,6 @@ extern struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 extern void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list);
 extern void mark_mounts_for_expiry(struct list_head *mounts);
 
-extern dev_t name_to_dev_t(char *name);
+extern dev_t name_to_dev_t(const char *name);
 
 #endif /* _LINUX_MOUNT_H */
diff --git a/init/do_mounts.c b/init/do_mounts.c
index a51cddc..69d74ff 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -145,6 +145,13 @@ static dev_t devt_from_partuuid(const char *uuid_str)
 		clear_root_wait = true;
 		goto done;
 	}
+	if (uuid_str[cmp.len - 1] == '\n') {
+		cmp.len--;
+		if (!cmp.len) {
+			clear_root_wait = true;
+			goto done;
+		}
+	}
 
 	dev = class_find_device(&block_class, NULL, &cmp,
 				&match_dev_by_uuid);
@@ -204,12 +211,13 @@ done:
  *	bangs.
  */
 
-dev_t name_to_dev_t(char *name)
+dev_t name_to_dev_t(const char *name)
 {
 	char s[32];
 	char *p;
 	dev_t res = 0;
 	int part;
+	int n;
 
 #ifdef CONFIG_BLOCK
 	if (strncmp(name, "PARTUUID=", 9) == 0) {
@@ -230,7 +238,7 @@ dev_t name_to_dev_t(char *name)
 				goto fail;
 		} else {
 			res = new_decode_dev(simple_strtoul(name, &p, 16));
-			if (*p)
+			if (*p && *p != '\n')
 				goto fail;
 		}
 		goto done;
@@ -238,15 +246,20 @@ dev_t name_to_dev_t(char *name)
 
 	name += 5;
 	res = Root_NFS;
-	if (strcmp(name, "nfs") == 0)
+	if (strncmp(name, "nfs", 3) == 0)
 		goto done;
 	res = Root_RAM0;
-	if (strcmp(name, "ram") == 0)
+	if (strncmp(name, "ram", 3) == 0)
 		goto done;
 
-	if (strlen(name) > 31)
+	n = strlen(name);
+	if (n != 0 && name[n - 1] == '\n')
+		n--;
+	if (n > 31)
 		goto fail;
-	strcpy(s, name);
+	strncpy(s, name, n);
+	s[n] = '\0';
+
 	for (p = s; *p; p++)
 		if (*p == '/')
 			*p = '!';
-- 
1.7.9.5

Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t

[Andrew Morton]

On Thu,  3 Oct 2013 14:10:37 -0700 Sebastian Capella <sebastian.capella@linaro.org> wrote:

> Enhance name_to_dev_t to handle trailing newline characters
> on device paths.  Some inputs to name_to_dev_t may come from
> userspace where oftentimes a '\n' is appended to the path.
> Added const to the name buffer in both the function
> declaration and the prototype to reflect input buffer
> handling.
> 
> By handling trailing newlines in name_to_dev_t, userspace
> buffers may be directly passed to name_to_dev_t without
> modification.

We have lib/string.c:strim() - perhaps this patch would be
neater if it were to use it?

Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t

[Eric W. Biederman]

Sebastian Capella <sebastian.capella@linaro.org> writes:

> Quoting Sebastian Capella (2013-10-03 16:47:35)
>> Quoting Sebastian Capella (2013-10-03 14:42:46)
>> > Quoting Andrew Morton (2013-10-03 14:15:23)
>> > > On Thu,  3 Oct 2013 14:10:37 -0700 Sebastian Capella <sebastian.capella@linaro.org> wrote:
>> > > 
>> > > > Enhance name_to_dev_t to handle trailing newline characters
>> > > > on device paths.  Some inputs to name_to_dev_t may come from
>> > > > userspace where oftentimes a '\n' is appended to the path.
>> > > > Added const to the name buffer in both the function
>> > > > declaration and the prototype to reflect input buffer
>> > > > handling.
>> > > > 
>> > > > By handling trailing newlines in name_to_dev_t, userspace
>> > > > buffers may be directly passed to name_to_dev_t without
>> > > > modification.
>> > > 
>> > > We have lib/string.c:strim() - perhaps this patch would be
>> > > neater if it were to use it?
>> > 
>> > Hi Morton,
>> > 
>> > I was intending to respect the const handling of the input buffer.
>> > 
>> > The actual buffer in this case is not really const as it comes from
>> > the file buffering, but removing the const requires changing the
>> > store function defined in the kobj_attribute, and would propagate
>> > to many areas in the kernel.
>> > 
>> > Modifying the buffer and removing the const was also suggested by Pavel.
>> > After some discussion I posted this version which did not change the
>> > buffer or the prototype.
>> > 
>> > Please let me know if the preference is to modify the store function
>> > definition.
>> > 
>> > I'll prepare a patchset that removes the consts to see how much is
>> > changed.
>> > 
>> > Thanks,
>> > 
>> > Sebastian
>> 
>> Hi Andrew,
>> 
>> Sorry for calling you Morton earlier.
>> 
>> I looked into removing the const from the store function, but I'm not sure
>> this is the right idea, so I'm going to shelf that for now.
>> 
>> Please let me know your thoughts.
>> 
>> Thanks,
>> 
>> Sebastian
>  
> Ping...
>
> Hi Andrew,
>
> Do you have any feedback on this?
>
> Below are the three options considered thus far.  Do
> you have any additional suggestions or preferences?

What is wrong with requiring userspace to use echo -n ?

That by far seems the simplest and least error prone solution.

Eric

Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t

[Andrew Morton]

On Tue, 28 Jan 2014 10:59:26 -0800 Sebastian Capella <sebastian.capella@linaro.org> wrote:

> > Do you have any feedback for me on this?
> > 
> > I'm happy do make any changes you think are correct, but I'm unsure if
> > you're asking me for option #3 above.  It's quite an intrusive change,
> > and changes old, established code and I'd like confirmation that's what
> > you'd like before proceeding down that path.
> > 
> > I've submitted patches with both options #1 and #2 above.
> > 
> > Thanks,
> > 
> > Sebastian
> 
> Ping.
> 
> Sorry for the lapse in attention to this.
> 
> Could you please clarify what is needed for this to be acceptable?
> I'm a little confused about what is being asked of me.

The problem is that kernel/power/hibernate.c:resume_store() is handed a
newline-terminated string, yes?  And if it blindly hands that string
over to name_to_dev_t(), name_to_dev_t() fails because the string is
wrong.

This is an oddity of the sysfs->kernel interface and altering
name_to_dev_t doesn't really seem appropriate for this problem - it
would be better to fix the caller to pass in the correct string.

Something like...

/*
 * Clean up a string which may have leading and/or trailing whitespace (as
 * defined by isspace()) by trimming off that whitespace.  Returns an address
 * which the caller must kfree(), or NULL on error.
 */
char *strim_copy(const char *s, gfp_t gfp)
{
	char *ret = kstrdup(skip_spaces(s), gfp);

	if (ret)
		strim(ret);
	return ret;
}
EXPORT_SYMBOL(strim_copy);

Re: [PATCH v3 1/2] init/do_mounts.c: ignore final \n in name_to_dev_t

[Andrew Morton]

On Wed, 29 Jan 2014 10:29:56 -0800 Sebastian Capella <sebastian.capella@linaro.org> wrote:

> Hi Andrew,
> 
> By the way, I do see a call (sysfs_streq) in use for this purpose
> other places.  Sorry, I didn't find it while looking at the original
> problem.  I'm not sure if this is preferable, but it appears to have
> been added specifically for the strings coming through sysfs.

Yes, I wrote it ;)

I didn't think sysfs_streq() is well suited to this problem.  And the
issue of possibly-null-terminated-strings coming in from userspace is a
common one, so it is desirable that we build up the suite of utilities
to handle this.

There are probably quite a lot of open-coded \n trimming loops which
can be cleaned up using such tools.

	grep -r "if .* == '\\\n'" .

> My preference is copying the string and cleaning it up before passing
> it to internal functions, even though we incur an allocation.

Yes.  Here on the kernel/userspace boundary we are typically running in
GFP_KERNEL context and the code is not performance critical - it is a
good fit.

[PATCH v3 2/2] PM / Hibernate: use name_to_dev_t to parse resume

[Sebastian Capella]

Use the name_to_dev_t call to parse the device name echo'd to
to /sys/power/resume.  This imitates the method used in hibernate.c
in software_resume, and allows the resume partition to be specified
using other equivalent device formats as well.  By allowing
/sys/debug/resume to accept the same syntax as the resume=device
parameter, we can parse the resume=device in the init script and
use the resume device directly from the kernel command line.

Signed-off-by: Sebastian Capella <sebastian.capella@linaro.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Len Brown <len.brown@intel.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
---
 kernel/power/hibernate.c |   15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index c9c759d..a29d2a7 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -972,16 +972,11 @@ static ssize_t resume_show(struct kobject *kobj, struct kobj_attribute *attr,
 static ssize_t resume_store(struct kobject *kobj, struct kobj_attribute *attr,
 			    const char *buf, size_t n)
 {
-	unsigned int maj, min;
 	dev_t res;
-	int ret = -EINVAL;
 
-	if (sscanf(buf, "%u:%u", &maj, &min) != 2)
-		goto out;
-
-	res = MKDEV(maj,min);
-	if (maj != MAJOR(res) || min != MINOR(res))
-		goto out;
+	res = name_to_dev_t(buf);
+	if (res == 0)
+		return -EINVAL;
 
 	lock_system_sleep();
 	swsusp_resume_device = res;
@@ -989,9 +984,7 @@ static ssize_t resume_store(struct kobject *kobj, struct kobj_attribute *attr,
 	printk(KERN_INFO "PM: Starting manual resume from disk\n");
 	noresume = 0;
 	software_resume();
-	ret = n;
- out:
-	return ret;
+	return n;
 }
 
 power_attr(resume);
-- 
1.7.9.5