[merged mm-nonmm-stable] mm-util-fix-possible-race-condition-in-kstrdup.patch removed from -mm tree

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The quilt patch titled
     Subject: mm/util: fix possible race condition in kstrdup()
has been removed from the -mm tree.  Its filename was
     mm-util-fix-possible-race-condition-in-kstrdup.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Yafang Shao <laoar.shao@xxxxxxxxx>
Subject: mm/util: fix possible race condition in kstrdup()
Date: Mon, 7 Oct 2024 22:49:09 +0800

In kstrdup(), it is critical to ensure that the dest string is always
NUL-terminated.  However, potential race condition can occur between a
writer and a reader.

Consider the following scenario involving task->comm:

    reader                    writer

  len = strlen(s) + 1;
                             strlcpy(tsk->comm, buf, sizeof(tsk->comm));
  memcpy(buf, s, len);

In this case, there is a race condition between the reader and the writer.
The reader calculates the length of the string `s` based on the old value
of task->comm.  However, during the memcpy(), the string `s` might be
updated by the writer to a new value of task->comm.

If the new task->comm is larger than the old one, the `buf` might not be
NUL-terminated.  This can lead to undefined behavior and potential
security vulnerabilities.

Let's fix it by explicitly adding a NUL terminator after the memcpy.  It
is worth noting that memcpy() is not atomic, so the new string can be
shorter when memcpy() already copied past the new NUL.

Link: https://lkml.kernel.org/r/20241007144911.27693-6-laoar.shao@xxxxxxxxx
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Alejandro Colomar <alx@xxxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Justin Stitt <justinstitt@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Matus Jokay <matus.jokay@xxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: Quentin Monnet <qmo@xxxxxxxxxx>
Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Cc: Simon Horman <horms@xxxxxxxxxx>
Cc: Stephen Smalley <stephen.smalley.work@xxxxxxxxx>
Cc: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/util.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/util.c~mm-util-fix-possible-race-condition-in-kstrdup
+++ a/mm/util.c
@@ -62,8 +62,15 @@ char *kstrdup(const char *s, gfp_t gfp)
 
 	len = strlen(s) + 1;
 	buf = kmalloc_track_caller(len, gfp);
-	if (buf)
+	if (buf) {
 		memcpy(buf, s, len);
+		/*
+		 * During memcpy(), the string might be updated to a new value,
+		 * which could be longer than the string when strlen() is
+		 * called. Therefore, we need to add a NUL terminator.
+		 */
+		buf[len - 1] = '\0';
+	}
 	return buf;
 }
 EXPORT_SYMBOL(kstrdup);
_

Patches currently in -mm which might be from laoar.shao@xxxxxxxxx are






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