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copy_tree: carefully treat permissions

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The setuid, setgid, and sticky bits are not copied during copy_tree.

Also start with very restrictive permissions before setting ownerships.

This prevents situations in which users in a group with less permissions
than others could win a race in opening the file before permissions are
removed again.

Proof of concept:

$ echo $HOME
/home/uwu
$ install -o uwu -g fandom -m 604 /dev/null /home/uwu/owo
$ ls -l /home/uwu/owo
-rw----r-- 1 uwu fandom 0 Sep  4 00:00 /home/uwu/owo

If /tmp is on another filesystem, then "usermod -md /tmp/uwu uwu" leads
to this temporary situation:

$ ls -l /tmp/uwu/owo
-rw----r-- 1 root root  0 Sep  4 00:00 /tmp/uwu/owo

This means that between openat and chownat_if_needed a user of group
fandom could open /tmp/uwu/owo and read the content when it is finally
written into the file.
This commit is contained in:
Samanta Navarro 2022-09-10 11:58:15 +00:00 committed by Iker Pedrosa
parent f33e7def06
commit cde221b858
1 changed files with 8 additions and 11 deletions
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19
libmisc/copydir.c
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@ -522,15 +522,14 @@ static int copy_dir (const struct path_info *src, const struct path_info *dst,
return -1; return -1;
} }
#endif /* WITH_SELINUX */ #endif /* WITH_SELINUX */
if ( (mkdirat (dst->dirfd, dst->name, statp->st_mode) != 0) if ( (mkdirat (dst->dirfd, dst->name, 0700) != 0)
|| (chownat_if_needed (dst, statp, || (chownat_if_needed (dst, statp,
old_uid, new_uid, old_gid, new_gid) != 0) old_uid, new_uid, old_gid, new_gid) != 0)
|| (fchmodat (dst->dirfd, dst->name, statp->st_mode & 07777, AT_SYMLINK_NOFOLLOW) != 0)
#ifdef WITH_ACL #ifdef WITH_ACL
|| ( (perm_copy_path (src, dst, &ctx) != 0) || ( (perm_copy_path (src, dst, &ctx) != 0)
&& (errno != 0)) && (errno != 0))
#else /* !WITH_ACL */ #endif /* WITH_ACL */
|| (fchmodat (dst->dirfd, dst->name, statp->st_mode & 07777, AT_SYMLINK_NOFOLLOW) != 0)
#endif /* !WITH_ACL */
#ifdef WITH_ATTR #ifdef WITH_ATTR
/* /*
* If the third parameter is NULL, all extended attributes * If the third parameter is NULL, all extended attributes
@ -719,12 +718,11 @@ static int copy_special (const struct path_info *src, const struct path_info *ds
if ( (mknodat (dst->dirfd, dst->name, statp->st_mode & ~07777U, statp->st_rdev) != 0) if ( (mknodat (dst->dirfd, dst->name, statp->st_mode & ~07777U, statp->st_rdev) != 0)
|| (chownat_if_needed (dst, statp, || (chownat_if_needed (dst, statp,
old_uid, new_uid, old_gid, new_gid) != 0) old_uid, new_uid, old_gid, new_gid) != 0)
|| (fchmodat (dst->dirfd, dst->name, statp->st_mode & 07777, AT_SYMLINK_NOFOLLOW) != 0)
#ifdef WITH_ACL #ifdef WITH_ACL
|| ( (perm_copy_path (src, dst, &ctx) != 0) || ( (perm_copy_path (src, dst, &ctx) != 0)
&& (errno != 0)) && (errno != 0))
#else /* !WITH_ACL */ #endif /* WITH_ACL */
|| (fchmodat (dst->dirfd, dst->name, statp->st_mode & 07777, AT_SYMLINK_NOFOLLOW) != 0)
#endif /* !WITH_ACL */
#ifdef WITH_ATTR #ifdef WITH_ATTR
/* /*
* If the third parameter is NULL, all extended attributes * If the third parameter is NULL, all extended attributes
@ -810,16 +808,15 @@ static int copy_file (const struct path_info *src, const struct path_info *dst,
return -1; return -1;
} }
#endif /* WITH_SELINUX */ #endif /* WITH_SELINUX */
ofd = openat (dst->dirfd, dst->name, O_WRONLY | O_CREAT | O_EXCL | O_TRUNC | O_NOFOLLOW | O_CLOEXEC, statp->st_mode & 07777); ofd = openat (dst->dirfd, dst->name, O_WRONLY | O_CREAT | O_EXCL | O_TRUNC | O_NOFOLLOW | O_CLOEXEC, 0600);
if ( (ofd < 0) if ( (ofd < 0)
|| (fchown_if_needed (ofd, statp, || (fchown_if_needed (ofd, statp,
old_uid, new_uid, old_gid, new_gid) != 0) old_uid, new_uid, old_gid, new_gid) != 0)
|| (fchmod (ofd, statp->st_mode & 07777) != 0)
#ifdef WITH_ACL #ifdef WITH_ACL
|| ( (perm_copy_fd (src->full_path, ifd, dst->full_path, ofd, &ctx) != 0) || ( (perm_copy_fd (src->full_path, ifd, dst->full_path, ofd, &ctx) != 0)
&& (errno != 0)) && (errno != 0))
#else /* !WITH_ACL */ #endif /* WITH_ACL */
|| (fchmod (ofd, statp->st_mode & 07777) != 0)
#endif /* !WITH_ACL */
#ifdef WITH_ATTR #ifdef WITH_ATTR
/* /*
* If the third parameter is NULL, all extended attributes * If the third parameter is NULL, all extended attributes