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<old>eh I have a very weird behavior of guile

<old>where I do a (environ (list ...)) followed by a (setenv key value)

<old>sometime values in (environ) disapear

<old>I fix this by doing: (environ (cons "key=value" (list ...)))

<old>this seems to be after a GC ..

<old>I have a minial reproducer

<old>this is super weird

<old>can someone try it ?

<old> https://paste.sr.ht/~old/ee09c33a57bd9c5803740215024a63c4de2cb57e

<old>should get a line: In execvp of ls: No such file or directory

<old>the bug is not in 2.2.7

<old>but in 3.0.7 and 3.0.9

<haugh>not in 3.0.5 either, fwiw

<old>hmm okay

<old>I have a backtrace

<old>seems like the GC think that strings in environ can be reeused

<old>so it get trashed

<old>this is a high risk of vulnerability

<old>anything could be put in environ

<old>I think that `putenv' in libc somehow realloc environ on a putenv call

<old>Guile set environ to be a scm_gc_malloc pointer which has GC allocated pointer in it

<old>Since glibc change the environ pointer, Guile start garbage collecting the string pointer that was in environ, since there's no reference to them

<old>However, glibc did memcpy them into the new environ, so there's dangling pointers

<old>yup that what's happening. libc is setting anew pointer in environ while copying the pointer owned by Guile

<dsmith>old, Nice find

<cow_2001>i end up importing a ton of stuff from guile when using r7rs ~_~

<dsmith>sneek, nickometer ]

<dsmith>!nickometer ]

<sneek>"]" is 15.66% lame, because 1 unbalanced bracket, 1 extraneous symbol

<singpolyma>!nickometer 💐🌹🥀🌷🌺🌸🏵️🌻🌼💮

<sneek>"\U01f490\U01f339\U01f940\U01f337\U01f33a\U01f338\U01f3f5️\U01f33b\U01f33c\U01f4ae" is 99.99% lame, because 11 consecutive non-alphas, 11 extraneous symbols

<sudden>!nickometer sudden

<sneek>"sudden" is 0% lame

<old>dsmith: I wonder what is the correct fix for that

<old>The obvious solution would be to only use the setenv/putenv/unsetenv/clearenv as defined by POSIX

<old>and to not use any Guile pointers in environ

<old>I'm not sure, gotta read the spec about what happen to these string in libc

<dsmith>Wow! The bothandled unicode nicely without crashing.

<dsmith>old, I'm not up on all the subtleties of the GC, but there is probably a way to tell it not to mess with the environment.

<old>looking a glibc code, strings allocated with setenv are never freed from memory

<old>awesome leak

<old>not only that, but glibc internally protect the access to the `environ' with a mutex.

<old>Guile simply overwrite that pointer. This is undefined behavior

<old>did not know that these function were so bad optimized

<old>even copying environ is actually undefined behavior on multi-threading

<old>ehh this is a pain

<old>sent a patch for it

IRC channel logs

2023-04-08.log