Req #80214 [Opn]: random_bytes(): 0 random bytes should be a valid request

Edit report at https://bugs.php.net/bug.php?id=80214&edit=1 ID: 80214 User updated by: divinity76 at gmail dot com Reported by: divinity76 at gmail dot com Summary: random_bytes(): 0 random bytes should be a valid request Status: Open Type: Feature/Change Request Package: Unknown/Other Function PHP Version: Next Minor Version Block user comment: N Private report: N New Comment: @rtrtrtrtrt at least the Linux Kernel developers think it's ok to ask for 0 random bytes, when you ask the linux kernel getrandom() api ( https://man7.org/linux/man-pages/man2/getrandom.2.html ) for 0 random, it will check that you're capable of generating random bytes, then.. generate 0 random bytes, and return the number of bytes it generated... 0, and not set any error notice anywhere (not in the return value itself, and not in errno) testing it: hans@xDevAd:~/projects/misc$ cat ggg.cpp #include <iostream> #include <sys/random.h> #include <errno.h> #include <unistd.h> #include <sys/syscall.h> /* For SYS_xxx definitions */ int main(){ std::string buf; std::cout << "errno before: " << errno << std::endl; const int flags = 0; std::cout << "libc getrandom: " << getrandom((char*)buf.data(), buf.size(), flags) << std::endl; std::cout << "errno after: " << errno << std::endl; std::cout << "syscall getrandom (practically bypassing libc): " << syscall(SYS_getrandom, (char*)buf.data(), buf.size(), flags) << std::endl; std::cout << "errno after: " << errno << std::endl; } hans@xDevAd:~/projects/misc$ g++ -Wall -Wextra -Wpedantic -Werror ggg.cpp hans@xDevAd:~/projects/misc$ ./a.out errno before: 0 libc getrandom: 0 errno after: 0 syscall getrandom (practically bypassing libc): 0 errno after: 0 hans@xDevAd:~/projects/misc$ - if the linux kernel had a problem with any of this, one of the numbers should have been <0 Previous Comments: ------------------------------------------------------------------------ [2020-10-15 09:50:29] nikic@php.net FWIW I agree that random_bytes(0) should be legal. ------------------------------------------------------------------------ [2020-10-15 09:32:05] rtrtrtrtrt at dfdfdfdf dot dfd > it's ok to request a string to be repeated 0 times, > but it's not ok to ask for 0 random bytes? you still don#t get the difference of a random string operation and a function which is meant for for cryptographic safe randomness meat for security relevant context are you sure that you don't absue random_bytes() at all in your sue case which likely don't need randomness in that quality > is that the opinion of you guys? yes > or do you guys consider str_repeat() broken in this regard? no or how is it a security context line random_bytes()? ------------------------------------------------------------------------ [2020-10-15 09:19:36] divinity76 at gmail dot com let me get this straight guys, requesting str_repeat("A",0) will give you an empty string, as one would expect (request: repeat "A" 0 times) requesting random_bytes(0) will give you an exception... (request: give me 0 random bytes) and both of these make sense to you? it's ok to request a string to be repeated 0 times, but it's not ok to ask for 0 random bytes? is that the opinion of you guys? or do you guys consider str_repeat() broken in this regard? ------------------------------------------------------------------------ [2020-10-15 03:32:54] a at b dot c dot de Scenario: I have a block of bytes that I want to pad to a specific length by appending some randomness (after embedding the message length) because the length of the message would otherwise be a potential information leak. The most straightforward way of doing it would be " . random_bytes(strlen($message) % BLOCK_SIZE)". To claim that random_bytes(0) should be special-cased is like claiming if() statements should be written to protect sort() from an empty array argument. ------------------------------------------------------------------------ [2020-10-10 12:42:03] rtrtrtrtrt at dfdfdfdf dot dfd seriously what value do you expect by random_bytes(0) > there are situations where code will dynamically > determine that they need "0 random bytes" your example below makes no sense at all - that's what the if-statement is for > none of those requests are errors > why is it then an error to ask for 0 random bytes beause it's not a random string operation but asking fro cryptographic save random and in no valid real world usecase you really want to operate with an empty string ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=80214 -- Edit this bug report at https://bugs.php.net/bug.php?id=80214&edit=1