From: Kees Cook <keescook@chromium.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
Christoph Hellwig <hch@lst.de>,
Nathan Chancellor <natechancellor@gmail.com>,
Tejun Heo <tj@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Shuah Khan <shuah@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org,
clang-built-linux@googlegroups.com,
Michal Hocko <mhocko@suse.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Lee Duncan <lduncan@suse.com>, Chris Leech <cleech@redhat.com>,
Adam Nichols <adam@grimm-co.com>,
linux-hardening@vger.kernel.org
Subject: [PATCH v4 2/3] seq_file: Fix clang warning for NULL pointer arithmetic
Date: Thu, 1 Apr 2021 15:13:19 -0700 [thread overview]
Message-ID: <20210401221320.2717732-3-keescook@chromium.org> (raw)
In-Reply-To: <20210401221320.2717732-1-keescook@chromium.org>
From: Arnd Bergmann <arnd@arndb.de>
Clang points out that adding something to NULL is not allowed in
standard C:
fs/kernfs/file.c:127:15: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return NULL + !*ppos;
~~~~ ^
fs/seq_file.c:529:14: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
return NULL + (*pos == 0);
Rephrase the code to be extra explicit about the valid, giving them
named SEQ_OPEN_EOF and SEQ_OPEN_SINGLE definitions. The instance in
kernfs was copied from single_start, so fix both at once.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Fixes: c2b19daf6760 ("sysfs, kernfs: prepare read path for kernfs")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201028151202.3074398-1-arnd@kernel.org
---
fs/kernfs/file.c | 9 ++++++---
fs/seq_file.c | 5 ++++-
include/linux/seq_file.h | 6 ++++++
3 files changed, 16 insertions(+), 4 deletions(-)
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index c75719312147..721bcbc1d4d0 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -122,10 +122,13 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
return next;
} else {
/*
- * The same behavior and code as single_open(). Returns
- * !NULL if pos is at the beginning; otherwise, NULL.
+ * The same behavior and code as single_open(). Continues
+ * if pos is at the beginning; otherwise, NULL.
*/
- return NULL + !*ppos;
+ if (*ppos)
+ return NULL;
+
+ return SEQ_OPEN_SINGLE;
}
}
diff --git a/fs/seq_file.c b/fs/seq_file.c
index cb11a34fb871..1b5bd95d0a48 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -542,7 +542,10 @@ EXPORT_SYMBOL(seq_dentry);
static void *single_start(struct seq_file *p, loff_t *pos)
{
- return NULL + (*pos == 0);
+ if (*pos)
+ return NULL;
+
+ return SEQ_OPEN_SINGLE;
}
static void *single_next(struct seq_file *p, void *v, loff_t *pos)
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index b83b3ae3c877..51c870765bfd 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -37,6 +37,12 @@ struct seq_operations {
#define SEQ_SKIP 1
+/*
+ * op->start must return a non-NULL pointer for single_open(),
+ * this is used when we don't care about the specific value.
+ */
+#define SEQ_OPEN_SINGLE ((void *)1)
+
/**
* seq_has_overflowed - check if the buffer has overflowed
* @m: the seq_file handle
--
2.25.1
next prev parent reply other threads:[~2021-04-01 22:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 22:13 [PATCH v4 0/3] sysfs: Unconditionally use vmalloc for buffer Kees Cook
2021-04-01 22:13 ` [PATCH v4 1/3] lkdtm/heap: Add vmalloc linear overflow test Kees Cook
2021-04-01 22:13 ` Kees Cook [this message]
2021-04-01 22:13 ` [PATCH v4 3/3] sysfs: Unconditionally use vmalloc for buffer Kees Cook
2021-04-02 6:32 ` Christoph Hellwig
2021-04-02 21:23 ` Kees Cook
2021-04-05 14:05 ` [sysfs] 5f65c1f63b: WARNING:at_fs/sysfs/file.c:#sysfs_kf_seq_start kernel test robot
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