From: Matthew Wilcox <willy@infradead.org>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Justin He <Justin.He@arm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Jonathan Corbet <corbet@lwn.net>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Luca Coelho <luciano.coelho@intel.com>,
Kalle Valo <kvalo@codeaurora.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Johannes Berg <johannes.berg@intel.com>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>
Subject: Re: [PATCH RFCv2 2/3] lib/vsprintf.c: make %pD print full path for file
Date: Sun, 30 May 2021 16:18:23 +0100 [thread overview]
Message-ID: <YLOsvz8ZbpjfcuGO@casper.infradead.org> (raw)
In-Reply-To: <89fc3919-ca2c-50fd-35e1-33bf3a59b993@rasmusvillemoes.dk>
On Fri, May 28, 2021 at 10:06:37PM +0200, Rasmus Villemoes wrote:
> On 28/05/2021 16.22, Justin He wrote:
> >
> >> From: Matthew Wilcox <willy@infradead.org>
>
> >> How is it "safer"? You already have a buffer passed from the caller.
> >> Are you saying that d_path_fast() might overrun a really small buffer
> >> but won't overrun a 256 byte buffer?
> > No, it won't overrun a 256 byte buf. When the full path size is larger than 256, the p->len is < 0 in prepend_name, and this overrun will be
> > dectected in extract_string() with "-ENAMETOOLONG".
> >
> > Each printk contains 2 vsnprintf. vsnprintf() returns the required size after formatting the string.>
> > 1. vprintk_store() will invoke 1st vsnprintf() will 8 bytes space to get the reserve_size. In this case, the _buf_ could be less than _end_ by design.
> > 2. Then it invokes 2nd printk_sprint()->vscnprintf()->vsnprintf() to really fill the space.
>
> Please do not assume that printk is the only user of vsnprintf() or the
> only one that would use a given %p<foo> extension.
>
> Also, is it clear that nothing can change underneath you in between two
> calls to vsnprintf()? IOW, is it certain that the path will fit upon a
> second call using the size returned from the first?
No, but that's also true of %s. I think vprintk_store() is foolish to
do it this way.
next prev parent reply other threads:[~2021-05-30 15:19 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-28 11:39 [PATCH RFCv2 0/3] make '%pD' print full path for file Jia He
2021-05-28 11:39 ` [PATCH RFCv2 1/3] fs: introduce helper d_path_fast() Jia He
2021-05-28 12:44 ` Al Viro
2021-05-28 12:51 ` Matthew Wilcox
2021-05-28 14:23 ` Justin He
2021-05-28 11:39 ` [PATCH RFCv2 2/3] lib/vsprintf.c: make %pD print full path for file Jia He
2021-05-28 12:59 ` Matthew Wilcox
2021-05-28 14:22 ` Justin He
2021-05-28 14:52 ` Matthew Wilcox
2021-05-28 15:09 ` Justin He
2021-05-28 15:22 ` Matthew Wilcox
2021-05-31 0:39 ` Justin He
2021-06-01 14:42 ` Justin He
2021-06-01 15:30 ` Matthew Wilcox
2021-06-01 15:36 ` Andy Shevchenko
2021-06-01 15:44 ` Matthew Wilcox
2021-06-01 15:53 ` Andy Shevchenko
2021-06-01 16:10 ` Andy Shevchenko
2021-06-01 17:05 ` Matthew Wilcox
2021-06-01 19:01 ` Rasmus Villemoes
2021-06-02 5:47 ` Justin He
2021-05-28 20:06 ` Rasmus Villemoes
2021-05-30 15:18 ` Matthew Wilcox [this message]
2021-05-31 9:40 ` Petr Mladek
2021-05-28 11:39 ` [PATCH RFCv2 3/3] s390/hmcdrv: remove the redundant directory path in debug message Jia He
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