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authorEugene Syromiatnikov <esyr@redhat.com>2019-09-11 18:45:40 +0100
committerChristian Brauner <christian.brauner@ubuntu.com>2019-09-12 14:56:33 +0200
commita0eb9abd8af92d1aa34bc1e24dfbd1ba0bd6a56c (patch)
treeb4e8d8523ac5dd6bd19a603ebb2b35a9852114be
parentf74c2bb98776e2de508f4d607cd519873065118e (diff)
fork: block invalid exit signals with clone3()
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, 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. This commit adds a check to copy_clone_args_from_user() to verify that the exit signal is limited by CSIGNAL as with legacy clone() and that the signal is valid. With this we don't get the legacy clone behavior were an invalid signal could be handed down and would only be detected and ignored in do_notify_parent(). Users of clone3() will now get a proper error when they pass an invalid exit signal. Note, that this is not user-visible behavior since no kernel with clone3() has been released yet. The following program will cause a splat on a non-fixed clone3() version and will fail correctly on a fixed version: #define _GNU_SOURCE #include <linux/sched.h> #include <linux/types.h> #include <sched.h> #include <stdio.h> #include <stdlib.h> #include <sys/syscall.h> #include <sys/wait.h> #include <unistd.h> int main(int argc, char *argv[]) { pid_t pid = -1; struct clone_args args = {0}; args.exit_signal = -1; pid = syscall(__NR_clone3, &args, sizeof(struct clone_args)); if (pid < 0) exit(EXIT_FAILURE); if (pid == 0) exit(EXIT_SUCCESS); wait(NULL); exit(EXIT_SUCCESS); } Fixes: 7f192e3cd316 ("fork: add clone3") Reported-by: Oleg Nesterov <oleg@redhat.com> Suggested-by: Oleg Nesterov <oleg@redhat.com> Suggested-by: Dmitry V. Levin <ldv@altlinux.org> Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com> Link: https://lore.kernel.org/r/4b38fa4ce420b119a4c6345f42fe3cec2de9b0b5.1568223594.git.esyr@redhat.com [christian.brauner@ubuntu.com: simplify check and rework commit message] Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
-rw-r--r--kernel/fork.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 2852d0e76ea3..541fd805fb88 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 +2564,14 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
if (copy_from_user(&args, uargs, size))
return -EFAULT;
+ /*
+ * Verify that higher 32bits of exit_signal are unset and that
+ * it is a valid signal
+ */
+ if (unlikely((args.exit_signal & ~((u64)CSIGNAL)) ||
+ !valid_signal(args.exit_signal)))
+ return -EINVAL;
+
*kargs = (struct kernel_clone_args){
.flags = args.flags,
.pidfd = u64_to_user_ptr(args.pidfd),