LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Eugene Syromiatnikov <esyr@redhat.com>
To: linux-kernel@vger.kernel.org,
	Christian Brauner <christian@brauner.io>,
	Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Dmitry V. Levin" <ldv@altlinux.org>,
	Eric Biederman <ebiederm@xmission.com>
Subject: [PATCH v3] fork: check exit_signal passed in clone3() call
Date: Wed, 11 Sep 2019 18:45:40 +0100
Message-ID: <4b38fa4ce420b119a4c6345f42fe3cec2de9b0b5.1568223594.git.esyr@redhat.com> (raw)
In-Reply-To: <cover.1568223594.git.esyr@redhat.com>

Previously, higher 32 bits of exit_signal fields were lost when
copied to the kernel args structure (that uses int as a type for the
respective field).  Moreover, as Oleg has noted[1], exit_signal is used
unchecked, so it has to be checked for sanity before use; for the legacy
syscalls, applying CSIGNAL mask guarantees that it is at least non-negative;
however, there's no such thing is done in clone3() code path, and that can
break at least thread_group_leader.

Adding checks that user-passed exit_signal fits into int and passes
valid_signal() check solves both of these problems.

[1] https://lkml.org/lkml/2019/9/10/467

* kernel/fork.c (copy_clone_args_from_user): Fail with -EINVAL if
args.exit_signal is greater than UINT_MAX or is not a valid signal.
(_do_fork): Note that exit_signal is expected to be checked for the
sanity by the caller.

Fixes: 7f192e3cd316 ("fork: add clone3")
Reported-by: Oleg Nesterov <oleg@redhat.com>
Co-authored-by: Oleg Nesterov <oleg@redhat.com>
Co-authored-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
 kernel/fork.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 2852d0e..f98314b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2338,6 +2338,8 @@ struct mm_struct *copy_init_mm(void)
  *
  * It copies the process, and if successful kick-starts
  * it and waits for it to finish using the VM if required.
+ *
+ * args->exit_signal is expected to be checked for sanity by the caller.
  */
 long _do_fork(struct kernel_clone_args *args)
 {
@@ -2562,6 +2564,15 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 	if (copy_from_user(&args, uargs, size))
 		return -EFAULT;
 
+	/*
+	 * Two separate checks are needed, as valid_signal() takes unsigned long
+	 * as an argument, and struct kernel_clone_args uses int type
+	 * for the exit_signal field.
+	 */
+	if (unlikely((args.exit_signal > UINT_MAX) ||
+		     !valid_signal(args.exit_signal)))
+		return -EINVAL;
+
 	*kargs = (struct kernel_clone_args){
 		.flags		= args.flags,
 		.pidfd		= u64_to_user_ptr(args.pidfd),
-- 
2.1.4


  reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-11 17:45 Eugene Syromiatnikov
2019-09-11 17:45 ` Eugene Syromiatnikov [this message]
2019-09-12 16:51   ` Oleg Nesterov
2019-09-13 11:40   ` Christian Brauner

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=4b38fa4ce420b119a4c6345f42fe3cec2de9b0b5.1568223594.git.esyr@redhat.com \
    --to=esyr@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=christian@brauner.io \
    --cc=ebiederm@xmission.com \
    --cc=ldv@altlinux.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=oleg@redhat.com \
    --cc=peterz@infradead.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git