linux-kernel - RE: [PATCH] FS: Fixed buffer overflow issue in seq

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Message-ID: <FB8A4655DFD2B34DB16AE06DDDD6C0E21BDBB7CD@SJEXCHMB12.corp.ad.broadcom.com>
Date:	Tue, 19 Nov 2013 21:22:58 +0000
From:	"Charley (Hao Chuan) Chu" <charley.chu@...adcom.com>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Al Viro" <viro@...iv.linux.org.uk>
cc:	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] FS: Fixed buffer overflow issue in seq_read()

> m->from is a red herring - it's not even looked at if m->count is 0.  

Then, shall the initialization here be removed too?

@@ -90,7 +90,7 @@ static int traverse(struct seq_file *m, loff_t offset)
 
        m->version = 0;
        index = 0;
-       m->count = m->from = 0;
+       m->count = 0;
        if (!offset) {
                m->index = index;
                return 0;

> What do you think about then just abstracing out that now common sequence 
> of re-allocating a larger buffer, while clearing m->count?

Following code is duplicated (slightly different) in both seq_read() and seq_lseek().
It would be nice to have them consolidated in traverse().

                while ((err = traverse(m, *ppos)) == -EAGAIN)
                        ;   
                if (err) {
                        /* With prejudice... */
                        m->read_pos = 0;
                        m->version = 0;
                        m->index = 0;
                        m->count = 0;
                        goto Done;
                } else {
                        m->read_pos = *ppos;
                }   

Thanks,
Charley

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