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Violators will be prosecuted for from ; Mon, 27 Feb 2017 23:00:57 -0000 From: Greg Kurz Date: Tue, 28 Feb 2017 00:00:17 +0100 In-Reply-To: <1488236421-30983-1-git-send-email-groug@kaod.org> References: <1488236421-30983-1-git-send-email-groug@kaod.org> Message-Id: <1488236421-30983-28-git-send-email-groug@kaod.org> Subject: [Qemu-devel] [PULL 27/31] 9pfs: local: symlink: don't follow symlinks List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell , "Aneesh Kumar K.V" , Greg Kurz The local_symlink() callback is vulnerable to symlink attacks because it calls: (1) symlink() which follows symbolic links for all path elements but the rightmost one (2) open(O_NOFOLLOW) which follows symbolic links for all path elements but the rightmost one (3) local_set_xattr()->setxattr() which follows symbolic links for all path elements (4) local_set_mapped_file_attr() which calls in turn local_fopen() and mkdir(), both functions following symbolic links for all path elements but the rightmost one This patch converts local_symlink() to rely on opendir_nofollow() and symlinkat() to fix (1), openat(O_NOFOLLOW) to fix (2), as well as local_set_xattrat() and local_set_mapped_file_attrat() to fix (3) and (4) respectively. This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi --- hw/9pfs/9p-local.c | 81 +++++++++++++++++------------------------------------- 1 file changed, 25 insertions(+), 56 deletions(-) diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index 7c197417ebff..907ecc59d494 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -978,23 +978,22 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath, V9fsPath *dir_path, const char *name, FsCred *credp) { int err = -1; - int serrno = 0; - char *newpath; - V9fsString fullname; - char *buffer = NULL; + int dirfd; - v9fs_string_init(&fullname); - v9fs_string_sprintf(&fullname, "%s/%s", dir_path->data, name); - newpath = fullname.data; + dirfd = local_opendir_nofollow(fs_ctx, dir_path->data); + if (dirfd == -1) { + return -1; + } /* Determine the security model */ - if (fs_ctx->export_flags & V9FS_SM_MAPPED) { + if (fs_ctx->export_flags & V9FS_SM_MAPPED || + fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) { int fd; ssize_t oldpath_size, write_size; - buffer = rpath(fs_ctx, newpath); - fd = open(buffer, O_CREAT|O_EXCL|O_RDWR|O_NOFOLLOW, SM_LOCAL_MODE_BITS); + + fd = openat_file(dirfd, name, O_CREAT | O_EXCL | O_RDWR, + SM_LOCAL_MODE_BITS); if (fd == -1) { - err = fd; goto out; } /* Write the oldpath (target) to the file. */ @@ -1002,78 +1001,48 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath, do { write_size = write(fd, (void *)oldpath, oldpath_size); } while (write_size == -1 && errno == EINTR); + close_preserve_errno(fd); if (write_size != oldpath_size) { - serrno = errno; - close(fd); - err = -1; goto err_end; } - close(fd); /* Set cleint credentials in symlink's xattr */ - credp->fc_mode = credp->fc_mode|S_IFLNK; - err = local_set_xattr(buffer, credp); - if (err == -1) { - serrno = errno; - goto err_end; - } - } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) { - int fd; - ssize_t oldpath_size, write_size; - buffer = rpath(fs_ctx, newpath); - fd = open(buffer, O_CREAT|O_EXCL|O_RDWR|O_NOFOLLOW, SM_LOCAL_MODE_BITS); - if (fd == -1) { - err = fd; - goto out; - } - /* Write the oldpath (target) to the file. */ - oldpath_size = strlen(oldpath); - do { - write_size = write(fd, (void *)oldpath, oldpath_size); - } while (write_size == -1 && errno == EINTR); + credp->fc_mode = credp->fc_mode | S_IFLNK; - if (write_size != oldpath_size) { - serrno = errno; - close(fd); - err = -1; - goto err_end; + if (fs_ctx->export_flags & V9FS_SM_MAPPED) { + err = local_set_xattrat(dirfd, name, credp); + } else { + err = local_set_mapped_file_attrat(dirfd, name, credp); } - close(fd); - /* Set cleint credentials in symlink's xattr */ - credp->fc_mode = credp->fc_mode|S_IFLNK; - err = local_set_mapped_file_attr(fs_ctx, newpath, credp); if (err == -1) { - serrno = errno; goto err_end; } - } else if ((fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) || - (fs_ctx->export_flags & V9FS_SM_NONE)) { - buffer = rpath(fs_ctx, newpath); - err = symlink(oldpath, buffer); + } else if (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH || + fs_ctx->export_flags & V9FS_SM_NONE) { + err = symlinkat(oldpath, dirfd, name); if (err) { goto out; } - err = lchown(buffer, credp->fc_uid, credp->fc_gid); + err = fchownat(dirfd, name, credp->fc_uid, credp->fc_gid, + AT_SYMLINK_NOFOLLOW); if (err == -1) { /* * If we fail to change ownership and if we are * using security model none. Ignore the error */ if ((fs_ctx->export_flags & V9FS_SEC_MASK) != V9FS_SM_NONE) { - serrno = errno; goto err_end; - } else + } else { err = 0; + } } } goto out; err_end: - remove(buffer); - errno = serrno; + unlinkat_preserve_errno(dirfd, name, 0); out: - g_free(buffer); - v9fs_string_free(&fullname); + close_preserve_errno(dirfd); return err; } -- 2.7.4