mirror of
https://git.tartarus.org/simon/putty.git
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61 lines
2.2 KiB
C
61 lines
2.2 KiB
C
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/*
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* Create a directory accessible only to us, and then check afterwards
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* that we really did end up with a directory with the right ownership
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* and permissions.
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*
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* The idea is that this is a directory in which we're about to create
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* something sensitive, like a listening Unix-domain socket for SSH
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* connection sharing or an SSH agent. We want to be protected against
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* somebody else previously having created the directory in a way
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* that's writable to us, and thus manipulating us into creating the
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* actual socket in a directory they can see so that they can connect
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* to it and (say) use our authenticated SSH sessions.
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*
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* NOTE: The strategy used in this function is not safe if the enemy
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* has unrestricted write access to the containing directory. In that
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* case, they could move our directory out of the way and make a new
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* one, after this function returns and before we create our socket
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* (or whatever) inside it.
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*
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* But this should be OK for temp directories (which modify the
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* default world-write behaviour by also setting the 't' bit,
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* preventing people from renaming or deleting things in there that
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* they don't own). And of course it's also safe if the directory is
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* writable only by our _own_ uid.
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*/
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#include <errno.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include "putty.h"
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char *make_dir_and_check_ours(const char *dirname)
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{
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struct stat st;
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/*
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* Create the directory. We might have created it before, so
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* EEXIST is an OK error; but anything else is doom.
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*/
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if (mkdir(dirname, 0700) < 0 && errno != EEXIST)
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return dupprintf("%s: mkdir: %s", dirname, strerror(errno));
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/*
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* Stat the directory and check its ownership and permissions.
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*/
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if (stat(dirname, &st) < 0)
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return dupprintf("%s: stat: %s", dirname, strerror(errno));
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if (st.st_uid != getuid())
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return dupprintf("%s: directory owned by uid %d, not by us",
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dirname, st.st_uid);
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if ((st.st_mode & 077) != 0)
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return dupprintf("%s: directory has overgenerous permissions %03o"
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" (expected 700)", dirname, st.st_mode & 0777);
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return NULL;
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}
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