Commit f5c16f29 authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman

sysfs: make sure read buffer is zeroed

13c589d5 ("sysfs: use seq_file when reading regular files")
switched sysfs from custom read implementation to seq_file to enable
later transition to kernfs.  After the change, the buffer passed to
->show() is acquired through seq_get_buf(); unfortunately, this
introduces a subtle behavior change.  Before the commit, the buffer
passed to ->show() was always zero as it was allocated using
get_zeroed_page().  Because seq_file doesn't clear buffers on
allocation and neither does seq_get_buf(), after the commit, depending
on the behavior of ->show(), we may end up exposing uninitialized data
to userland thus possibly altering userland visible behavior and
leaking information.

Fix it by explicitly clearing the buffer.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarRon <ron@debian.org>
Fixes: 13c589d5 ("sysfs: use seq_file when reading regular files")
Cc: stable <stable@vger.kernel.org> # 3.13+
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 555724a8
......@@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
ssize_t count;
char *buf;
/* acquire buffer and ensure that it's >= PAGE_SIZE */
/* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
count = seq_get_buf(sf, &buf);
if (count < PAGE_SIZE) {
seq_commit(sf, -1);
return 0;
}
memset(buf, 0, PAGE_SIZE);
/*
* Invoke show(). Control may reach here via seq file lseek even
......
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