On 17/10/2018 15:35, Eric W. Biederman wrote:
Alan Jenkins <alan.christopher.jenkins@xxxxxxxxx> writes:
On 17/10/2018 14:20, David Howells wrote:
David Howells <dhowells@xxxxxxxxxx> wrote:
I should probably check that the picked point is actually a mountpoint.
The root of the mount object at the path specified, that is, perhaps with
something like the attached.
David
I agree. I'm happy to see this is using the same check as do_remount().
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/
Davids check will work for bind mounts as well. It just won't work it
just won't work for files or subdirectories of some mountpoint.
Eric
I see. Then I am still happy to see the fspick() check match a check in
do_remount() (and it still solves the problem I was worried about).
I cannot blame David for the do_remount() comment being out of date :-).
# uname -r
4.18.10-200.fc.28.x86_64
# mount --bind /mnt /mnt
# mount -oremount,debug /mnt
# findmnt /mnt; findmnt /
[findmnt shows / has been remounted, adding the ext4 "debug" mount option]
---
diff --git a/fs/fsopen.c b/fs/fsopen.c
index f673e93ac456..aaaaa17a233c 100644
--- a/fs/fsopen.c
+++ b/fs/fsopen.c
@@ -186,6 +186,10 @@ SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags
if (ret < 0)
goto err;
+ ret = -EINVAL;
+ if (target.mnt->mnt_root != target.dentry)
+ goto err_path;
+
fc = vfs_new_fs_context(target.dentry->d_sb->s_type, target.dentry,
0, 0, FS_CONTEXT_FOR_RECONFIGURE);
if (IS_ERR(fc)) {
