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Ensure that qfile-unpacker never traverses symbolic links in files being unpacked #114

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Merged
marmarek merged 2 commits into from
Jun 28, 2024
Merged

Ensure that qfile-unpacker never traverses symbolic links in files being unpacked #114

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edece29
Do not use path containing "/" in linkat() or stat()
DemiMarie May 20, 2024
075dfe4
Do not use fchmodat() because it follows symlinks
DemiMarie May 8, 2024
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34 changes: 13 additions & 21 deletions qrexec-lib/unpack.c
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,6 @@ static long validate_utime_nsec(uint32_t untrusted_nsec)

static void fix_times_and_perms(const int fd,
const struct file_header *const untrusted_hdr,
const char *const last_segment,
const char *const untrusted_name)
{
const struct timespec times[2] =
Expand All @@ -144,21 +143,12 @@ static void fix_times_and_perms(const int fd,
.tv_nsec = validate_utime_nsec(untrusted_hdr->mtime_nsec)
},
};
if (last_segment == NULL) {
/* Do not change the mode of symbolic links */
if (!S_ISLNK(untrusted_hdr->mode) &&
/* Do not change the mode of symbolic links */
if (!S_ISLNK(untrusted_hdr->mode) &&
fchmod(fd, untrusted_hdr->mode & 07777))
do_exit(errno, untrusted_name);
if (futimens(fd, times)) /* as above */
do_exit(errno, untrusted_name);
} else {
/* Do not change the mode of what a symbolic link points to */
if (!S_ISLNK(untrusted_hdr->mode) &&
fchmodat(fd, last_segment, untrusted_hdr->mode & 07777, 0))
do_exit(errno, untrusted_name);
if (utimensat(fd, last_segment, times, AT_SYMLINK_NOFOLLOW)) /* as above */
do_exit(errno, untrusted_name);
}
do_exit(errno, untrusted_name);
if (futimens(fd, times)) /* as above */
do_exit(errno, untrusted_name);
}

// Open the second-to-last component of a path, enforcing O_NOFOLLOW for every
Expand Down Expand Up @@ -226,8 +216,6 @@ void process_one_file_reg(struct file_header *untrusted_hdr,
fdout = openat(safe_dirfd, last_segment, O_WRONLY | O_CREAT | O_EXCL | O_NOFOLLOW | O_CLOEXEC | O_NOCTTY, 0000);
if (fdout < 0)
do_exit(errno, untrusted_name);
if (safe_dirfd != AT_FDCWD)
close(safe_dirfd);

/* sizes are signed elsewhere */
if (untrusted_hdr->filelen > LLONG_MAX || (bytes_limit && untrusted_hdr->filelen > bytes_limit))
Expand All @@ -251,10 +239,12 @@ void process_one_file_reg(struct file_header *untrusted_hdr,
char fd_str[11];
if ((unsigned)snprintf(fd_str, sizeof(fd_str), "%d", fdout) >= sizeof(fd_str))
abort();
if (linkat(procdir_fd, fd_str, AT_FDCWD, untrusted_name, AT_SYMLINK_FOLLOW) < 0)
if (linkat(procdir_fd, fd_str, safe_dirfd, last_segment, AT_SYMLINK_FOLLOW) < 0)
do_exit(errno, untrusted_name);
}
fix_times_and_perms(fdout, untrusted_hdr, NULL, untrusted_name);
fix_times_and_perms(fdout, untrusted_hdr, untrusted_name);
if (safe_dirfd != AT_FDCWD)
close(safe_dirfd);
close(fdout);
free(path_dup);
}
Expand All @@ -281,11 +271,13 @@ void process_one_file_dir(struct file_header *untrusted_hdr,
}
if (errno != EEXIST)
do_exit(errno, untrusted_name);
if (stat(untrusted_name,&buf) < 0)
int new_dirfd = openat(safe_dirfd, last_segment, O_RDONLY | O_NOFOLLOW | O_CLOEXEC | O_DIRECTORY);
if (new_dirfd < 0 || fstat(new_dirfd, &buf) < 0)
do_exit(errno, untrusted_name);
total_bytes += buf.st_size;
/* size accumulated after the fact, so don't check limit here */
fix_times_and_perms(safe_dirfd, untrusted_hdr, last_segment, untrusted_name);
fix_times_and_perms(new_dirfd, untrusted_hdr, untrusted_name);
close(new_dirfd);
if (safe_dirfd != AT_FDCWD)
close(safe_dirfd);
free(path_dup);
Expand Down