Messages in this thread | | | Date | Mon, 19 May 2014 15:25:00 -0700 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH driver-core-linus] sysfs: make sure read buffer is zeroed |
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On Mon, May 19, 2014 at 03:52:10PM -0400, Tejun Heo wrote: > 13c589d5b0ac ("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: Tejun Heo <tj@kernel.org> > Reported-by: Ron <ron@debian.org> > Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files") > --- > fs/sysfs/file.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c > index 28cc1acd..e9ef59b 100644 > --- a/fs/sysfs/file.c > +++ b/fs/sysfs/file.c > @@ -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
Thanks, I'll go queue this up.
greg k-h
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