GNU bug report logs - #50070
chmod reads uninitialized variables when fts_info is an error and -v is set, leading to random error messages

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From: Michael Debertol <michael.debertol <at> gmail.com>
To: 50070 <at> debbugs.gnu.org
Subject: bug#50070: chmod reads uninitialized variables when fts_info is an error and -v is set, leading to random error messages
Date: Sun, 15 Aug 2021 22:15:58 +0200

Hi,

I noticed that when running chmod with -v on a dangling symlink the 
error message is somewhat random:

> ln -s file-that-does-not-exist lnk

> chmod -w lnk -v

> chmod: cannot operate on dangling symlink 'lnk'

> failed to change mode of 'lnk' from 0000 (---------) to 7777 (rwsrwsrwt)

> chmod -w lnk -v

> chmod: cannot operate on dangling symlink 'lnk'

> failed to change mode of 'lnk' from 0000 (---------) to 7775 (rwsrwsr-t)

> chmod -w lnk -v

> chmod: cannot operate on dangling symlink 'lnk'

> failed to change mode of 'lnk' from 0000 (---------) to 7774 (rwsrwsr-T)


(note that the value for "to" is different)

This appears to be because in the process_file function, old_mode and 
new_mode are only set when ok is true. When chmod encounters a dangling 
symlink, ok will be false and old_mode/new_mode won't be set. However, 
old_mode and new_mode are still accessed for the invocation of 
describe_change if verbosity is set to high, leading to incorrect error 
messages.

I think a better behavior could be to not print the "from mode to mode" 
part of the error message if the file could not be accessed, since it is 
meaningless anyways.

Have a nice day,

Michael

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