Add strndup_user() to LinuxKPI <linux/string.h>

[• hselasky]

Assuming there is no special case for n = 0.

[jfree]

Added simple error checking

[• hselasky]

Looks good!

[markj]

sys/compat/linuxkpi/common/include/linux/string.h

107

There's no need for this check, memdup_user() will handle it. A user-supplied pointer can never be trusted, so there's no real reason to check for NULL specifically (it could be 0x1, or any other invalid value).

[jfree]

Removed NULL pointer error checking thanks to @markj. General user pointers are safely checked in memdup_user().

[• hselasky]

sys/compat/linuxkpi/common/include/linux/string.h

109

I think "n" excludes the NUL character.

Why can't you simply do:

return (memdup_user_nul(ustr, n));

[jfree]

Used memdup_user_nul() instead of memdup_user() to duplicate memory from userspace. Relevant documentation can be found here:

https://www.kernel.org/doc/html/v5.0/core-api/kernel-api.html