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sysfs: correctly handle short reads on PREALLOC attrs. 

attributes declared with __ATTR_PREALLOC use sysfs_kf_read()
which ignores the 'count' arg.
So a 1-byte read request can return more bytes than that.

This is seen with the 'dash' shell when 'read' is used on
some 'md' sysfs attributes.

So only return the 'min' of count and the attribute length.

Signed-off-by: NeilBrown <neilb@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
NeilBrown 2015-08-06 08:27:55 +10:00 committed by Greg Kroah-Hartman
parent cfcf6a91aa
commit 65da3484d9
1 changed files with 3 additions and 1 deletions
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4
fs/sysfs/file.c
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@ -108,6 +108,7 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
{ {
const struct sysfs_ops *ops = sysfs_file_ops(of->kn); const struct sysfs_ops *ops = sysfs_file_ops(of->kn);
struct kobject *kobj = of->kn->parent->priv; struct kobject *kobj = of->kn->parent->priv;
size_t len;
/* /*
* If buf != of->prealloc_buf, we don't know how * If buf != of->prealloc_buf, we don't know how
@ -115,7 +116,8 @@ static ssize_t sysfs_kf_read(struct kernfs_open_file *of, char *buf,
*/ */
if (pos || WARN_ON_ONCE(buf != of->prealloc_buf)) if (pos || WARN_ON_ONCE(buf != of->prealloc_buf))
return 0; return 0;
return ops->show(kobj, of->kn->priv, buf); len = ops->show(kobj, of->kn->priv, buf);
return min(count, len);
} }
/* kernfs write callback for regular sysfs files */ /* kernfs write callback for regular sysfs files */