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c5abfe08fc
Patch series "fork: do not expose incomplete mm on fork".
During fork we may place the virtual memory address space into an
inconsistent state before the fork operation is complete.
In addition, we may encounter an error during the fork operation that
indicates that the virtual memory address space is invalidated.
As a result, we should not be exposing it in any way to external machinery
that might interact with the mm or VMAs, machinery that is not designed to
deal with incomplete state.
We specifically update the fork logic to defer khugepaged and ksm to the
end of the operation and only to be invoked if no error arose, and
disallow uffd from observing fork events should an error have occurred.
This patch (of 2):
Currently on fork we expose the virtual address space of a process to
userland unconditionally if uffd is registered in VMAs, regardless of
whether an error arose in the fork.
This is performed in dup_userfaultfd_complete() which is invoked
unconditionally, and performs two duties - invoking registered handlers
for the UFFD_EVENT_FORK event via dup_fctx(), and clearing down
userfaultfd_fork_ctx objects established in dup_userfaultfd().
This is problematic, because the virtual address space may not yet be
correctly initialised if an error arose.
The change in commit d24062914837 ("fork: use __mt_dup() to duplicate
maple tree in dup_mmap()") makes this more pertinent as we may be in a
state where entries in the maple tree are not yet consistent.
We address this by, on fork error, ensuring that we roll back state that
we would otherwise expect to clean up through the event being handled by
userland and perform the memory freeing duty otherwise performed by
dup_userfaultfd_complete().
We do this by implementing a new function, dup_userfaultfd_fail(), which
performs the same loop, only decrementing reference counts.
Note that we perform mmgrab() on the parent and child mm's, however
userfaultfd_ctx_put() will mmdrop() this once the reference count drops to
zero, so we will avoid memory leaks correctly here.
Bug: 254441685
Link: https://lkml.kernel.org/r/cover.1729014377.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/d3691d58bb58712b6fb3df2be441d175bd3cdf07.1729014377.git.lorenzo.stoakes@oracle.com
Fixes: d24062914837 ("fork: use __mt_dup() to duplicate maple tree in dup_mmap()")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: Jann Horn <jannh@google.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit f64e67e5d3a45a4a04286c47afade4b518acd47b)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I9c2f774a0f4a0a75729b86c77c627fb38b8bb17b
How do I submit patches to Android Common Kernels
-
BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
EXPORT_SYMBOL_GPL()require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export. - When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
-
LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.
Common Kernel patch requirements
- All patches must conform to the Linux kernel coding standards and pass
scripts/checkpatch.pl - Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
- If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch:
UPSTREAM:,BACKPORT:,FROMGIT:,FROMLIST:, orANDROID:. - All patches must have a
Change-Id:tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html) - If an Android bug has been assigned, there must be a
Bug:tag. - All patches must have a
Signed-off-by:tag by the author and the submitter
Additional requirements are listed below based on patch type
Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:
- If the patch is a cherry-pick from Linux mainline with no changes at all
- tag the patch subject with
UPSTREAM:. - add upstream commit information with a
(cherry picked from commit ...)line - Example:
- if the upstream commit message is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
UPSTREAM: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch requires any changes from the upstream version, tag the patch with
BACKPORT:instead ofUPSTREAM:.- use the same tags as
UPSTREAM: - add comments about the changes under the
(cherry picked from commit ...)line - Example:
- use the same tags as
BACKPORT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
[joe: Resolved minor conflict in drivers/foo/bar.c ]
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for other backports: FROMGIT:, FROMLIST:,
- If the patch has been merged into an upstream maintainer tree, but has not yet
been merged into Linux mainline
- tag the patch subject with
FROMGIT: - add info on where the patch came from as
(cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't uselinux-nextfor example). - if changes were required, use
BACKPORT: FROMGIT: - Example:
- if the commit message in the maintainer tree is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
FROMGIT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
(cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch has been submitted to LKML, but not accepted into any maintainer tree
- tag the patch subject with
FROMLIST: - add a
Link:tag with a link to the submittal on lore.kernel.org - add a
Bug:tag with the Android bug (required for patches not accepted into a maintainer tree) - if changes were required, use
BACKPORT: FROMLIST: - Example:
- tag the patch subject with
FROMLIST: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for Android-specific patches: ANDROID:
- If the patch is fixing a bug to Android-specific code
- tag the patch subject with
ANDROID: - add a
Fixes:tag that cites the patch with the bug - Example:
- tag the patch subject with
ANDROID: fix android-specific bug in foobar.c
This is the detailed description of the important fix
Fixes: 1234abcd2468 ("foobar: add cool feature")
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch is a new feature
- tag the patch subject with
ANDROID: - add a
Bug:tag with the Android bug (required for android-specific features)
- tag the patch subject with