From 7bd698b3c04e61ee9e03d4c2a55003f75df14dca Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 9 Mar 2018 11:30:20 -0800 Subject: [PATCH] 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 Reviewed-by: Mimi Zohar Signed-off-by: James Morris --- fs/exec.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 7eb8d21bcab9..a919a827d181 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -895,14 +895,14 @@ 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); - if (ret) - return ret; - ret = deny_write_access(file); if (ret) return ret; + ret = security_kernel_read_file(file, id); + if (ret) + goto out; + i_size = i_size_read(file_inode(file)); if (max_size > 0 && i_size > max_size) { ret = -EFBIG;