| From | Greg Kroah-Hartman <> | Subject | [PATCH 4.4 113/113] sysfs: correctly handle read offset on PREALLOC attrs | Date | Mon, 5 Sep 2016 18:45:16 +0200 |
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4.4-stable review patch. If anyone has any objections, please let me know.
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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
commit 17d0774f80681020eccc9638d925a23f1fc4f671 upstream.
Attributes declared with __ATTR_PREALLOC use sysfs_kf_read() which returns zero bytes for non-zero offset. This breaks script checkarray in mdadm tool in debian where /bin/sh is 'dash' because its builtin 'read' reads only one byte at a time. Script gets 'i' instead of 'idle' when reads current action from /sys/block/$dev/md/sync_action and as a result does nothing.
This patch adds trivial implementation of partial read: generate whole string and move required part into buffer head.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Fixes: 4ef67a8c95f3 ("sysfs/kernfs: make read requests on pre-alloc files use the buffer.") Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950 Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/sysfs/file.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/fs/sysfs/file.c +++ b/fs/sysfs/file.c @@ -114,9 +114,15 @@ static ssize_t sysfs_kf_read(struct kern * If buf != of->prealloc_buf, we don't know how * large it is, so cannot safely pass it to ->show */ - if (pos || WARN_ON_ONCE(buf != of->prealloc_buf)) + if (WARN_ON_ONCE(buf != of->prealloc_buf)) return 0; len = ops->show(kobj, of->kn->priv, buf); + if (pos) { + if (len <= pos) + return 0; + len -= pos; + memmove(buf, buf + pos, len); + } return min(count, len); }
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