Commit 7bd698b3 authored Mar 09, 2018 by Kees Cook Committed by James Morris Mar 19, 2018

exec: Set file unwritable before LSM check



The LSM check should happen after the file has been confirmed to be
unchanging. Without this, we could have a race between the Time of Check
(the call to security_kernel_read_file() which could read the file and
make access policy decisions) and the Time of Use (starting with
kernel_read_file()'s reading of the file contents). In theory, file
contents could change between the two.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: James Morris <james.morris@microsoft.com>

parent 6b4f3d01

fs/exec.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -895,13 +895,13 @@ int kernel_read_file(struct file file, void buf, loff_t size,
		if (!S_ISREG(file_inode(file)->i_mode) \|\| max_size < 0)
		return -EINVAL;

		ret = security_kernel_read_file(file, id);
		ret = deny_write_access(file);
		if (ret)
		return ret;

		ret = deny_write_access(file);
		ret = security_kernel_read_file(file, id);
		if (ret)
		return ret;
		goto out;

		i_size = i_size_read(file_inode(file));
		if (max_size > 0 && i_size > max_size) {

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