[16/19] vfs: check fd has read access in kernel_read_file_from_fd()

Commit Message

Andrew Morton Oct. 18, 2021, 10:16 p.m. UTC

From: "Matthew Wilcox (Oracle)" <[e-mail]>
Subject: vfs: check fd has read access in kernel_read_file_from_fd()

If we open a file without read access and then pass the fd to a syscall
whose implementation calls kernel_read_file_from_fd(), we get a warning
from __kernel_read():

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))

This currently affects both finit_module() and kexec_file_load(), but it
could affect other syscalls in the future.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: b844f0ecbc56 ("vfs: define kernel_copy_file_from_fd()")
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Reported-by: Hao Sun <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Acked-by: Christian Brauner <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Mimi Zohar <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/kernel_read_file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Patch

--- a/fs/kernel_read_file.c~vfs-check-fd-has-read-access-in-kernel_read_file_from_fd
+++ a/fs/kernel_read_file.c
@@ -178,7 +178,7 @@  int kernel_read_file_from_fd(int fd, lof
 	struct fd f = fdget(fd);
 	int ret = -EBADF;
 
-	if (!f.file)
+	if (!f.file || !(f.file->f_mode & FMODE_READ))
 		goto out;
 
 	ret = kernel_read_file(f.file, offset, buf, buf_size, file_size, id);