e1bbcd277a
Hold writers when changing a mount's idmapping to make it more robust. The vfs layer takes care to retrieve the idmapping of a mount once ensuring that the idmapping used for vfs permission checking is identical to the idmapping passed down to the filesystem. For ioctl codepaths the filesystem itself is responsible for taking the idmapping into account if they need to. While all filesystems with FS_ALLOW_IDMAP raised take the same precautions as the vfs we should enforce it explicitly by making sure there are no active writers on the relevant mount while changing the idmapping. This is similar to turning a mount ro with the difference that in contrast to turning a mount ro changing the idmapping can only ever be done once while a mount can transition between ro and rw as much as it wants. This is a minor user-visible change. But it is extremely unlikely to matter. The caller must've created a detached mount via OPEN_TREE_CLONE and then handed that O_PATH fd to another process or thread which then must've gotten a writable fd for that mount and started creating files in there while the caller is still changing mount properties. While not impossible it will be an extremely rare corner-case and should in general be considered a bug in the application. Consider making a mount MOUNT_ATTR_NOEXEC or MOUNT_ATTR_NODEV while allowing someone else to perform lookups or exec'ing in parallel by handing them a copy of the OPEN_TREE_CLONE fd or another fd beneath that mount. Link: https://lore.kernel.org/r/20220510095840.152264-1-brauner@kernel.org Cc: Seth Forshee <seth.forshee@digitalocean.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> |
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|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.