From 43d3b56b2e8c6c6ffdd988187a096e5c24cb5a8b Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 19 May 2014 15:52:10 -0400 Subject: [PATCH] sysfs: make sure read buffer is zeroed commit f5c16f29bf5e57ba4051fc7785ba7f035f798c71 upstream. 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 Reported-by: Ron Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files") Signed-off-by: Greg Kroah-Hartman --- 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 810cf6e613e5..5fd2bf18e27d 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