* Re: Bug reporting [not found] <1621111620246345@mail.yandex.ru> @ 2021-05-05 22:37 ` Alejandro Colomar (man-pages) [not found] ` <1492841620310804@mail.yandex.ru> 0 siblings, 1 reply; 6+ messages in thread From: Alejandro Colomar (man-pages) @ 2021-05-05 22:37 UTC (permalink / raw) To: Dave Chupreev Cc: linux-man, GNU C Library, Michael Kerrisk (man-pages), Roland McGrath [ 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/ ^ permalink raw reply [flat|nested] 6+ messages in thread
[parent not found: <1492841620310804@mail.yandex.ru>]
* Re: Bug reporting [not found] ` <1492841620310804@mail.yandex.ru> @ 2021-05-09 16:40 ` Michael Kerrisk (man-pages) 2021-05-09 17:20 ` Alexander Monakov 0 siblings, 1 reply; 6+ messages in thread From: Michael Kerrisk (man-pages) @ 2021-05-09 16:40 UTC (permalink / raw) To: Dave Chupreev Cc: Alejandro Colomar (man-pages), linux-man, GNU C Library, Roland McGrath Hello, On Fri, 7 May 2021 at 02:21, Dave Chupreev <cdn.dev@yandex.ru> wrote: > > Well I see, I've tried on Linux and yea I didn't find any option to insert multiple definitions. I think the only way to insert multiple definitions is by direct manipulation of 'extern char **environ'. Thanks, Michael > 06.05.2021, 01:37, "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>: > > [ 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/ -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Bug reporting 2021-05-09 16:40 ` Michael Kerrisk (man-pages) @ 2021-05-09 17:20 ` Alexander Monakov 2021-05-09 17:58 ` Michael Kerrisk (man-pages) 0 siblings, 1 reply; 6+ messages in thread From: Alexander Monakov @ 2021-05-09 17:20 UTC (permalink / raw) To: mtk.manpages Cc: Dave Chupreev, Alejandro Colomar (man-pages), linux-man, GNU C Library, Roland McGrath On Mon, 10 May 2021, Michael Kerrisk (man-pages) via Libc-alpha wrote: > Hello, > > On Fri, 7 May 2021 at 02:21, Dave Chupreev <cdn.dev@yandex.ru> wrote: > > > > Well I see, I've tried on Linux and yea I didn't find any option to insert multiple definitions. > > I think the only way to insert multiple definitions is by direct > manipulation of 'extern char **environ'. You can cause a program to start with multiple definitions, because it is possible to pass arbitrarily funny stuff as 'envp' argument to execve, such as: - duplicated entries - entries without a '=' - entries starting with '=' - empty strings - "2 x 2 = 4" All of that will be present in the exec'd program's environment array. Alexander ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Bug reporting 2021-05-09 17:20 ` Alexander Monakov @ 2021-05-09 17:58 ` Michael Kerrisk (man-pages) 0 siblings, 0 replies; 6+ messages in thread From: Michael Kerrisk (man-pages) @ 2021-05-09 17:58 UTC (permalink / raw) To: Alexander Monakov Cc: Dave Chupreev, Alejandro Colomar (man-pages), linux-man, GNU C Library, Roland McGrath Hello ALexander, On Mon, 10 May 2021 at 05:20, Alexander Monakov <amonakov@ispras.ru> wrote: > > > > On Mon, 10 May 2021, Michael Kerrisk (man-pages) via Libc-alpha wrote: > > > Hello, > > > > On Fri, 7 May 2021 at 02:21, Dave Chupreev <cdn.dev@yandex.ru> wrote: > > > > > > Well I see, I've tried on Linux and yea I didn't find any option to insert multiple definitions. > > > > I think the only way to insert multiple definitions is by direct > > manipulation of 'extern char **environ'. > > You can cause a program to start with multiple definitions, because it is > possible to pass arbitrarily funny stuff as 'envp' argument to execve, such as: > > - duplicated entries > - entries without a '=' > - entries starting with '=' > - empty strings > - "2 x 2 = 4" > > All of that will be present in the exec'd program's environment array. Yes. I was too focussed on thinking about what an already running program can do to its current environment. Thanks for reminding me of the above. Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ ^ permalink raw reply [flat|nested] 6+ messages in thread
* Bug reporting @ 2004-08-09 23:38 Benno 2004-08-09 23:47 ` Roland McGrath 0 siblings, 1 reply; 6+ messages in thread From: Benno @ 2004-08-09 23:38 UTC (permalink / raw) To: libc-alpha The glibc documentation (eg: ./README) tells people to send bug reports to bug-glibc@gnu.org. The appears to no longer be the case, perhaps people should instead be pointed to: http://www.gnu.org/software/libc/bugs.html Cheers, Benno ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Bug reporting 2004-08-09 23:38 Benno @ 2004-08-09 23:47 ` Roland McGrath 0 siblings, 0 replies; 6+ messages in thread From: Roland McGrath @ 2004-08-09 23:47 UTC (permalink / raw) To: Benno; +Cc: libc-alpha > The glibc documentation (eg: ./README) tells people to send bug > reports to bug-glibc@gnu.org. The appears to no longer be the case, > perhaps people should instead be pointed to: > http://www.gnu.org/software/libc/bugs.html I will update the README file. If you find any other places in the current glibc CVS sources where the old pointers appear, please file a bug in bugzilla. I think I got them all before. Thanks, Roland ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-05-09 17:58 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <1621111620246345@mail.yandex.ru> 2021-05-05 22:37 ` Bug reporting Alejandro Colomar (man-pages) [not found] ` <1492841620310804@mail.yandex.ru> 2021-05-09 16:40 ` Michael Kerrisk (man-pages) 2021-05-09 17:20 ` Alexander Monakov 2021-05-09 17:58 ` Michael Kerrisk (man-pages) 2004-08-09 23:38 Benno 2004-08-09 23:47 ` Roland McGrath
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