Pull clone3 stack argument update from Christian Brauner: "This changes clone3() to do basic stack validation and to set up the stack depending on whether or not it is growing up or down. With clone3() the expectation is now very simply that the .stack argument points to the lowest address of the stack and that .stack_size specifies the initial stack size. This is diferent from legacy clone() where the "stack" argument had to point to the lowest or highest address of the stack depending on the architecture. clone3() was released with 5.3. Currently, it is not documented and very unclear to userspace how the stack and stack_size argument have to be passed. After talking to glibc folks we concluded that changing clone3() to determine stack direction and doing basic validation is the right course of action. Note, this is a potentially user visible change. In the very unlikely case, that it breaks someone's use-case we will revert. (And then e.g. place the new behavior under an appropriate flag.) Note that passing an empty stack will continue working just as before. Breaking someone's use-case is very unlikely. Neither glibc nor musl currently expose a wrapper for clone3(). There is currently also no real motivation for anyone to use clone3() directly. First, because using clone{3}() with stacks requires some assembly (see glibc and musl). Second, because it does not provide features that legacy clone() doesn't. New features for clone3() will first happen in v5.5 which is why v5.4 is still a good time to try and make that change now and backport it to v5.3. I did a codesearch on https://codesearch.debian.net, github, and gitlab and could not find any software currently relying directly on clone3(). I expect this to change once we land CLONE_CLEAR_SIGHAND which was a request coming from glibc at which point they'll likely start using it" * tag 'for-linus-2019-11-05' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: clone3: validate stack arguments
Showing the changes to include/uapi/linux (1 of 2 files). Show all
Unified · Split
| @@ -51,6 +51,10 @@ · 50 unmodified lines | |||
| 51 | * sent when the child exits. | 51 | * sent when the child exits. |
| 52 | * @stack: Specify the location of the stack for the | 52 | * @stack: Specify the location of the stack for the |
| 53 | * child process. | 53 | * child process. |
| 54 | * Note, @stack is expected to point to the | ||
| 55 | * lowest address. The stack direction will be | ||
| 56 | * determined by the kernel and set up | ||
| 57 | * appropriately based on @stack_size. | ||
| 54 | * @stack_size: The size of the stack for the child process. | 58 | * @stack_size: The size of the stack for the child process. |
| 55 | * @tls: If CLONE_SETTLS is set, the tls descriptor | 59 | * @tls: If CLONE_SETTLS is set, the tls descriptor |
| 56 | * is set to tls. | 60 | * is set to tls. |