From: Kees Cook <keescook@chromium.org>
To: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
Peter Zijlstra <peterz@infradead.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jens Axboe <axboe@kernel.dk>, Jann Horn <jannh@google.com>,
Jan Kara <jack@suse.cz>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: [PATCH] fs: WARN when f_count resurrection is attempted
Date: Fri, 3 May 2024 13:16:25 -0700 [thread overview]
Message-ID: <20240503201620.work.651-kees@kernel.org> (raw)
It should never happen that get_file() is called on a file with
f_count equal to zero. If this happens, a use-after-free condition
has happened[1], and we need to attempt a best-effort reporting of
the situation to help find the root cause more easily. Additionally,
this serves as a data corruption indicator that system owners using
warn_limit or panic_on_warn would like to have detected.
Link: https://lore.kernel.org/lkml/7c41cf3c-2a71-4dbb-8f34-0337890906fc@gmail.com/ [1]
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: Christian Brauner <brauner@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jann Horn <jannh@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: linux-fsdevel@vger.kernel.org
---
include/linux/fs.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 00fc429b0af0..fa9ea5390f33 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1038,7 +1038,8 @@ struct file_handle {
static inline struct file *get_file(struct file *f)
{
- atomic_long_inc(&f->f_count);
+ long prior = atomic_long_fetch_inc_relaxed(&f->f_count);
+ WARN_ONCE(!prior, "struct file::f_count incremented from zero; use-after-free condition present!\n");
return f;
}
--
2.34.1
next reply other threads:[~2024-05-03 20:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-03 20:16 Kees Cook [this message]
2024-05-04 9:43 ` [PATCH] fs: WARN when f_count resurrection is attempted Christian Brauner
2024-05-06 10:38 ` Peter Zijlstra
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