lkml.org 
[lkml]   [2019]   [Sep]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH v2] fork: check exit_signal passed in clone3() call
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.

Checking user-passed exit_signal against ~CSIGNAL mask 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 has bits set outside CSIGNAL mask.
(_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>
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
kernel/fork.c | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 2852d0e..9dee2ab 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 +2564,16 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
if (copy_from_user(&args, uargs, size))
return -EFAULT;

+ /*
+ * exit_signal is confined to CSIGNAL mask in legacy syscalls,
+ * so it is used unchecked deeper in syscall handling routines;
+ * moreover, copying to struct kernel_clone_args.exit_signals
+ * trims higher 32 bits, so it is has to be checked that they
+ * are zero.
+ */
+ if (unlikely(args.exit_signal & ~((u64)CSIGNAL)))
+ return -EINVAL;
+
*kargs = (struct kernel_clone_args){
.flags = args.flags,
.pidfd = u64_to_user_ptr(args.pidfd),
--
2.1.4
\
 
 \ /
  Last update: 2019-09-10 20:00    [W:0.076 / U:0.508 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site