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Commit 7bd698b3 authored by Kees Cook's avatar Kees Cook Committed by James Morris
Browse files

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: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarMimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: default avatarJames 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) {