* [PATCH v2] fs: Validate umount flags before looking up path in ksys_umount
@ 2021-01-04 21:54 Sargun Dhillon
2021-01-05 8:06 ` Christoph Hellwig
0 siblings, 1 reply; 2+ messages in thread
From: Sargun Dhillon @ 2021-01-04 21:54 UTC (permalink / raw
To: Christoph Hellwig, Al Viro
Cc: Sargun Dhillon, Kyle Anderson, Manas Alekar, linux-fsdevel,
linux-api, Rob Gulewich, Zoran Simic, stable
ksys_umount was refactored to into split into another function
(path_umount) to enable sharing code. This changed the order that flags and
permissions are validated in, and made it so that user_path_at was called
before validating flags.
Unfortunately, libfuse2[1] and libmount[2] rely on the old flag validation
behaviour to determine whether or not the kernel supports UMOUNT_NOFOLLOW.
The other path that this validation is being checked on is
init_umount->path_umount->can_umount. That's all internal to the kernel. We
can safely move flag checking to ksys_umount, and let other users of
path_umount know they need to perform their own validation.
[1]: https://github.com/libfuse/libfuse/blob/9bfbeb576c5901b62a171d35510f0d1a922020b7/util/fusermount.c#L403
[2]: https://github.com/karelzak/util-linux/blob/7ed579523b556b1270f28dbdb7ee07dee310f157/libmount/src/context_umount.c#L813
Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Cc: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Fixes: 41525f56e256 ("fs: refactor ksys_umount")
---
fs/namespace.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index cebaa3e81794..752f82121dd4 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1710,8 +1710,6 @@ static int can_umount(const struct path *path, int flags)
{
struct mount *mnt = real_mount(path->mnt);
- if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
- return -EINVAL;
if (!may_mount())
return -EPERM;
if (path->dentry != path->mnt->mnt_root)
@@ -1725,6 +1723,13 @@ static int can_umount(const struct path *path, int flags)
return 0;
}
+
+/*
+ * path_umount - unmount by path
+ *
+ * path_umount does not check the validity of flags. It is up to the caller
+ * to ensure that it only contains valid umount options.
+ */
int path_umount(struct path *path, int flags)
{
struct mount *mnt = real_mount(path->mnt);
@@ -1746,6 +1751,10 @@ static int ksys_umount(char __user *name, int flags)
struct path path;
int ret;
+ /* Check flag validity first to allow probing of supported flags */
+ if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
+ return -EINVAL;
+
if (!(flags & UMOUNT_NOFOLLOW))
lookup_flags |= LOOKUP_FOLLOW;
ret = user_path_at(AT_FDCWD, name, lookup_flags, &path);
--
2.25.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] fs: Validate umount flags before looking up path in ksys_umount
2021-01-04 21:54 [PATCH v2] fs: Validate umount flags before looking up path in ksys_umount Sargun Dhillon
@ 2021-01-05 8:06 ` Christoph Hellwig
0 siblings, 0 replies; 2+ messages in thread
From: Christoph Hellwig @ 2021-01-05 8:06 UTC (permalink / raw
To: Sargun Dhillon
Cc: Christoph Hellwig, Al Viro, Kyle Anderson, Manas Alekar,
linux-fsdevel, linux-api, Rob Gulewich, Zoran Simic, stable
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2021-01-05 8:07 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2021-01-04 21:54 [PATCH v2] fs: Validate umount flags before looking up path in ksys_umount Sargun Dhillon
2021-01-05 8:06 ` Christoph Hellwig
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.