seq_file: fix incomplete reset on read from zero offset

BugLink: http://bugs.launchpad.net/bugs/1751131
commit cf5eebae2cd28d37581507668605f4d23cd7218d upstream.

When resetting iterator on a zero offset we need to discard any data
already in the buffer (count), and private state of the iterator (version).

For example this bug results in first line being repeated in /proc/mounts
if doing a zero size read before a non-zero size read.

Reported-by: Rich Felker <dalias@libc.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: e522751d605d ("seq_file: reset iterator to first record for zero offset")
Cc: <stable@vger.kernel.org> # v4.10
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 4be761c1a03d1f1dee3fb024a36c45e56df909af..eea09f6d883056b8e6fcc0aad857ab1a76fdb3f1 100644 (file)
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -181,8 +181,11 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
         * if request is to read from zero offset, reset iterator to first
         * record as it might have been already advanced by previous requests
         */
-       if (*ppos == 0)
+       if (*ppos == 0) {
                m->index = 0;
+               m->version = 0;
+               m->count = 0;
+       }
 
        /* Don't assume *ppos is where we left it */
        if (unlikely(*ppos != m->read_pos)) {