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From: Al Viro <viro@zeniv.linux.org.uk>
To: Alexander Potapenko <glider@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Borislav Petkov <bp@alien8.de>, Christoph Hellwig <hch@lst.de>,
	Christoph Lameter <cl@linux.com>,
	David Rientjes <rientjes@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Eric Dumazet <edumazet@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Kees Cook <keescook@chromium.org>, Marco Elver <elver@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Pekka Enberg <penberg@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Vegard Nossum <vegard.nossum@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Linux-MM <linux-mm@kvack.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Evgenii Stepanov <eugenis@google.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	Vitaly Buka <vitalybuka@google.com>,
	linux-toolchains <linux-toolchains@vger.kernel.org>
Subject: Re: [PATCH v4 43/45] namei: initialize parameters passed to step_into()
Date: Mon, 4 Jul 2022 14:55:06 +0100	[thread overview]
Message-ID: <YsLxOkApqKPQ8Bep@ZenIV> (raw)
In-Reply-To: <YsLuoFtki01gbmYB@ZenIV>

On Mon, Jul 04, 2022 at 02:44:00PM +0100, Al Viro wrote:
> On Mon, Jul 04, 2022 at 10:20:53AM +0200, Alexander Potapenko wrote:
> 
> > What makes you think they are false positives? Is the scenario I
> > described above:
> > 
> > """
> > In particular, if the call to lookup_fast() in walk_component()
> > returns NULL, and lookup_slow() returns a valid dentry, then the
> > `seq` and `inode` will remain uninitialized until the call to
> > step_into()
> > """
> > 
> > impossible?
> 
> Suppose step_into() has been called in non-RCU mode.  The first
> thing it does is
> 	int err = handle_mounts(nd, dentry, &path, &seq);
> 	if (err < 0) 
> 		return ERR_PTR(err);
> 
> And handle_mounts() in non-RCU mode is
> 	path->mnt = nd->path.mnt;
> 	path->dentry = dentry;
> 	if (nd->flags & LOOKUP_RCU) {
> 		[unreachable code]
> 	}
> 	[code not touching seqp]
> 	if (unlikely(ret)) {
> 		[code not touching seqp]
> 	} else {
> 		*seqp = 0; /* out of RCU mode, so the value doesn't matter */
> 	}
> 	return ret;

Make that
 	[code assigning ret a non-negative value and never using seqp]
 	if (unlikely(ret)) {
 		[code never using seqp or ret]
 	} else {
 		*seqp = 0; /* out of RCU mode, so the value doesn't matter */
 	}
 	return ret;

so if (err < 0) in the caller is equivalent to if (err).

  reply	other threads:[~2022-07-04 13:55 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20220701142310.2188015-1-glider@google.com>
2022-07-01 14:23 ` [PATCH v4 43/45] namei: initialize parameters passed to step_into() Alexander Potapenko
2022-07-02 17:23   ` Linus Torvalds
2022-07-03  3:59     ` Al Viro
2022-07-04  2:52     ` Al Viro
2022-07-04  8:20       ` Alexander Potapenko
2022-07-04 13:44         ` Al Viro
2022-07-04 13:55           ` Al Viro [this message]
2022-07-04 15:49           ` Alexander Potapenko
2022-07-04 16:03             ` Greg Kroah-Hartman
2022-07-04 16:33               ` Alexander Potapenko
2022-07-04 18:23             ` Segher Boessenkool
2022-07-04 16:00           ` Al Viro
2022-07-04 16:47             ` Alexander Potapenko
2022-07-04 17:36       ` Linus Torvalds
2022-07-04 19:02         ` Al Viro
2022-07-04 19:16           ` Linus Torvalds
2022-07-04 19:55             ` Al Viro
2022-07-04 20:24               ` Linus Torvalds
2022-07-04 20:46                 ` Al Viro
2022-07-04 20:51                   ` Linus Torvalds
2022-07-04 21:04                     ` Al Viro
2022-07-04 23:13                       ` [PATCH 1/7] __follow_mount_rcu(): verify that mount_lock remains unchanged Al Viro
2022-07-04 23:14                         ` [PATCH 2/7] follow_dotdot{,_rcu}(): change calling conventions Al Viro
2022-07-04 23:14                         ` [PATCH 3/7] namei: stash the sampled ->d_seq into nameidata Al Viro
2022-07-04 23:15                         ` [PATCH 4/7] step_into(): lose inode argument Al Viro
2022-07-04 23:15                         ` [PATCH 5/7] follow_dotdot{,_rcu}(): don't bother with inode Al Viro
2022-07-04 23:16                         ` [PATCH 6/7] lookup_fast(): " Al Viro
2022-07-04 23:17                         ` [PATCH 7/7] step_into(): move fetching ->d_inode past handle_mounts() Al Viro
2022-07-04 23:19                         ` [PATCH 1/7] __follow_mount_rcu(): verify that mount_lock remains unchanged Al Viro
2022-07-05  0:06                           ` Linus Torvalds
2022-07-05  3:48                             ` Al Viro
2022-07-04 20:47                 ` [PATCH v4 43/45] namei: initialize parameters passed to step_into() Linus Torvalds
2022-08-08 16:37   ` Alexander Potapenko

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