[v3] extensible syscalls: CHECK_FIELDS to allow for easier feature detection

[PATCH RFC v3 03/10] openat2: explicitly return -E2BIG for (usize > PAGE_SIZE)

Posted by Aleksa Sarai 1 month, 2 weeks ago

While we do currently return -EFAULT in this case, it seems prudent to
follow the behaviour of other syscalls like clone3. It seems quite
unlikely that anyone depends on this error code being EFAULT, but we can
always revert this if it turns out to be an issue.

Cc: <stable@vger.kernel.org> # v5.6+
Fixes: fddb5d430ad9 ("open: introduce openat2(2) syscall")
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 fs/open.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/open.c b/fs/open.c
index 22adbef7ecc2..30bfcddd505d 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1458,6 +1458,8 @@ SYSCALL_DEFINE4(openat2, int, dfd, const char __user *, filename,
 
 	if (unlikely(usize < OPEN_HOW_SIZE_VER0))
 		return -EINVAL;
+	if (unlikely(usize > PAGE_SIZE))
+		return -E2BIG;
 
 	err = copy_struct_from_user(&tmp, sizeof(tmp), how, usize);
 	if (err)

-- 
2.46.1

Re: [PATCH RFC v3 03/10] openat2: explicitly return -E2BIG for (usize > PAGE_SIZE)

Posted by Greg KH 1 month, 2 weeks ago

On Thu, Oct 10, 2024 at 07:40:36AM +1100, Aleksa Sarai wrote:
> While we do currently return -EFAULT in this case, it seems prudent to
> follow the behaviour of other syscalls like clone3. It seems quite
> unlikely that anyone depends on this error code being EFAULT, but we can
> always revert this if it turns out to be an issue.
> 
> Cc: <stable@vger.kernel.org> # v5.6+
> Fixes: fddb5d430ad9 ("open: introduce openat2(2) syscall")
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
>  fs/open.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/open.c b/fs/open.c
> index 22adbef7ecc2..30bfcddd505d 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1458,6 +1458,8 @@ SYSCALL_DEFINE4(openat2, int, dfd, const char __user *, filename,
>  
>  	if (unlikely(usize < OPEN_HOW_SIZE_VER0))
>  		return -EINVAL;
> +	if (unlikely(usize > PAGE_SIZE))
> +		return -E2BIG;
>  
>  	err = copy_struct_from_user(&tmp, sizeof(tmp), how, usize);
>  	if (err)
> 
> -- 
> 2.46.1

Why isn't this just sent as a normal fix to be included now and not
burried in a RFC series?

thanks,

greg k-h

Re: (subset) [PATCH RFC v3 03/10] openat2: explicitly return -E2BIG for (usize > PAGE_SIZE)

Posted by Christian Brauner 1 month, 2 weeks ago

On Thu, 10 Oct 2024 07:40:36 +1100, Aleksa Sarai wrote:
> While we do currently return -EFAULT in this case, it seems prudent to
> follow the behaviour of other syscalls like clone3. It seems quite
> unlikely that anyone depends on this error code being EFAULT, but we can
> always revert this if it turns out to be an issue.
> 
> 

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[03/10] openat2: explicitly return -E2BIG for (usize > PAGE_SIZE)
        https://git.kernel.org/vfs/vfs/c/f92f0a1b0569