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* Use lchown() instead of chown() in canonicalisePathMetaData(). This

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matters when running as root, since then we don't use the setuid
  helper (which already used lchown()).
  
* Also check for an obscure security problem on platforms that don't
  have lchown.  Then we can't change the ownership of symlinks, which
  doesn't matter *except* when the containing directory is writable by
  the owner (which is the case with the top-level Nix store directory).
This commit is contained in:
Eelco Dolstra 2006-12-09 20:02:27 +00:00
parent 5f681988f2
commit b17677462c
1 changed files with 38 additions and 8 deletions
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46
src/libstore/local-store.cc
View file

@ -6,6 +6,7 @@
#include "pathlocks.hh"
#include "aterm.hh"
#include "derivations-ast.hh"
#include "config.h"
#include <iostream>
#include <algorithm>
@ -213,7 +214,7 @@ void copyPath(const Path & src, const Path & dst)
}
void canonicalisePathMetaData(const Path & path)
static void _canonicalisePathMetaData(const Path & path)
{
checkInterrupt();
@ -221,13 +222,25 @@ void canonicalisePathMetaData(const Path & path)
if (lstat(path.c_str(), &st))
throw SysError(format("getting attributes of path `%1%'") % path);
if (!S_ISLNK(st.st_mode)) {
/* Change ownership to the current uid. If its a symlink, use
lchown if available, otherwise don't bother. Wrong ownership
of a symlink doesn't matter, since the owning user can't change
the symlink and can't delete it because the directory is not
writable. The only exception is top-level paths in the Nix
store (since that directory is group-writable for the Nix build
users group); we check for this case below. */
if (st.st_uid != geteuid()) {
#if HAVE_LCHOWN
if (lchown(path.c_str(), geteuid(), -1) == -1)
#else
if (!S_ISLNK(st.st_mode) &&
chown(path.c_str(), geteuid(), -1) == -1)
#endif
throw SysError(format("changing owner of `%1%' to %2%")
% path % geteuid());
}
if (st.st_uid != geteuid()) {
if (chown(path.c_str(), geteuid(), -1) == -1)
throw SysError(format("changing owner of `%1%' to %2%")
% path % geteuid());
}
if (!S_ISLNK(st.st_mode)) {
/* Mask out all type related bits. */
mode_t mode = st.st_mode & ~S_IFMT;
@ -253,7 +266,24 @@ void canonicalisePathMetaData(const Path & path)
if (S_ISDIR(st.st_mode)) {
Strings names = readDirectory(path);
for (Strings::iterator i = names.begin(); i != names.end(); ++i)
canonicalisePathMetaData(path + "/" + *i);
_canonicalisePathMetaData(path + "/" + *i);
}
}
void canonicalisePathMetaData(const Path & path)
{
_canonicalisePathMetaData(path);
/* On platforms that don't have lchown(), the top-level path can't
be a symlink, since we can't change its ownership. */
struct stat st;
if (lstat(path.c_str(), &st))
throw SysError(format("getting attributes of path `%1%'") % path);
if (st.st_uid != geteuid()) {
assert(S_ISLNK(st.st_mode));
throw Error(format("wrong ownership of top-level store path `%1%'") % path);
}
}