[ added a few CCs ] Hello Dave, On 5/5/21 10:30 PM, Dave Chupreev wrote: > Hello, Alejandro. > > On page 138 I guess you refer to TLPI, written by Michael. > > 1. > > Your version of /unsetenv() /should check to see whether there > are multiple definitions of an environment variable, and remove > them all. > > How can I add such variables which have many definitions? According to > *putenv* and *setenv* functions, variables with the same names are > replaced if encountered. I haven't read that part of the book yet, so I ignore the context. But AFAIK, that can't happen on Linux, as you pointed out (probably neither on Unix systems in general, but I don't know for sure, probably Michael does). I guess the only possibility is if an attacker somehow modified your environment and inserted multiple copies of an env variable. The book (TLPI) states that glibc does check that, so I digged into the sources and found that in <stdlib/setenv.c>, around line 290 (<https://sourceware.org/git?p=glibc.git;a=blob;f=stdlib/setenv.c;h=893f081af6b5a21b999a4056757fd69d1386c0d4;hb=HEAD#l290>). That behavior was introduced by Roland in commit 196980f5117c8d38f10d64bf67eeb0924651675f (<https://sourceware.org/git/?p=glibc.git;a=commit;h=196980f5117c8d38f10d64bf67eeb0924651675f>), so maybe he can better explain the reasons behind the change (the commit msg is quite unexplicative) if he still remembers (that goes back to 1995). Regards, Alex -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/
