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From: Alexander Potapenko <glider@google.com>
To: glider@google.com
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	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@googlegroups.com, linux-mm@kvack.org,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	Evgenii Stepanov <eugenis@google.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	Vitaly Buka <vitalybuka@google.com>,
	linux-toolchains@vger.kernel.org
Subject: [PATCH v4 43/45] namei: initialize parameters passed to step_into()
Date: Fri,  1 Jul 2022 16:23:08 +0200	[thread overview]
Message-ID: <20220701142310.2188015-44-glider@google.com> (raw)
In-Reply-To: <20220701142310.2188015-1-glider@google.com>

Under certain circumstances initialization of `unsigned seq` and
`struct inode *inode` passed into step_into() may be skipped.
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() (see [1] for more info).

Right now step_into() does not use these uninitialized values,
yet passing uninitialized values to functions is considered undefined
behavior (see [2]). To fix that, we initialize `seq` and `inode` at
definition.

[1] https://github.com/ClangBuiltLinux/linux/issues/1648#issuecomment-1146608063
[2] https://lore.kernel.org/linux-toolchains/CAHk-=whjz3wO8zD+itoerphWem+JZz4uS3myf6u1Wd6epGRgmQ@mail.gmail.com/

Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Marco Elver <elver@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Buka <vitalybuka@google.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-toolchains@vger.kernel.org
Signed-off-by: Alexander Potapenko <glider@google.com>
---
Link: https://linux-review.googlesource.com/id/I94d4e8cc1f0ecc7174659e9506ce96aaf2201d0a
---
 fs/namei.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 1f28d3f463c3b..6b39dfd3b41bc 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1995,8 +1995,8 @@ static const char *handle_dots(struct nameidata *nd, int type)
 static const char *walk_component(struct nameidata *nd, int flags)
 {
 	struct dentry *dentry;
-	struct inode *inode;
-	unsigned seq;
+	struct inode *inode = NULL;
+	unsigned seq = 0;
 	/*
 	 * "." and ".." are special - ".." especially so because it has
 	 * to be able to know about the current root directory and
@@ -3393,8 +3393,8 @@ static const char *open_last_lookups(struct nameidata *nd,
 	struct dentry *dir = nd->path.dentry;
 	int open_flag = op->open_flag;
 	bool got_write = false;
-	unsigned seq;
-	struct inode *inode;
+	unsigned seq = 0;
+	struct inode *inode = NULL;
 	struct dentry *dentry;
 	const char *res;
 
-- 
2.37.0.rc0.161.g10f37bed90-goog


       reply	other threads:[~2022-07-01 14:30 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 ` Alexander Potapenko [this message]
2022-07-02 17:23   ` [PATCH v4 43/45] namei: initialize parameters passed to step_into() 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
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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