On Fri, Nov 01, 2019 at 02:57:10PM +0000, Szabolcs Nagy wrote:
On 31/10/2019 11:36, Christian Brauner wrote:
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h index 99335e1f4a27..25b4fa00bad1 100644 --- a/include/uapi/linux/sched.h +++ b/include/uapi/linux/sched.h @@ -51,6 +51,10 @@
sent when the child exits.- @stack: Specify the location of the stack for the
child process.
Note, @stack is expected to point to the
lowest address. The stack direction will be
determined by the kernel and set up
appropriately based on @stack_size.- @stack_size: The size of the stack for the child process.
- @tls: If CLONE_SETTLS is set, the tls descriptor
is set to tls.diff --git a/kernel/fork.c b/kernel/fork.c index bcdf53125210..55af6931c6ec 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2561,7 +2561,35 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs, return 0; } -static bool clone3_args_valid(const struct kernel_clone_args *kargs) +/**
- clone3_stack_valid - check and prepare stack
- @kargs: kernel clone args
- Verify that the stack arguments userspace gave us are sane.
- In addition, set the stack direction for userspace since it's easy for us to
- determine.
- */
+static inline bool clone3_stack_valid(struct kernel_clone_args *kargs) +{
- if (kargs->stack == 0) {
if (kargs->stack_size > 0)return false;- } else {
if (kargs->stack_size == 0)return false;if (!access_ok((void __user *)kargs->stack, kargs->stack_size))return false;+#if !defined(CONFIG_STACK_GROWSUP) && !defined(CONFIG_IA64)
kargs->stack += kargs->stack_size;+#endif
- }
from the description it is not clear whose responsibility it is to guarantee the alignment of sp on entry.
Userspace.
i think 0 stack size may work if signals are blocked and then prohibiting it might not be the right thing.
Note that stack size 0 is allowed:
struct clone_args args = { .exit_signal = SIGCHLD, };
clone3(&args, sizeof(args));
will just work fine.
it's not clear how libc should deal with v5.3 kernels which don't have the stack+=stack_size logic.
stable is already Cced and the change will be backported to v5.3. Nearly all distros track pull in stable updates.
Florian, thoughts on this?
Christian