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h=From:Subject:Date:To:Cc; b=hir3URuDIttID8b5GJHAXggVkRnfATo9lrEzTpHHqRlEhyX0DQwT/JAE9Opz2z5Hf sOs7KLGhrV7UZS+cmcoHUTrJjiTFFi5aeccZryrOTG1zP0WOAGX/1jCdgvLabOcUi9 3Qmt77+PiLlYr7qsqB3Z2FZQtMXmBt0zjUReR9oimQQbIfe03d8Aoj+NtP8J7V9Z0J QXrY9rsbJLJ2qbsZNVRbQ5nTPzs1qXu0l/wUEE6juzjhyWtBi8OylIze2tKKW2S/Ay SFHPgpyuNBWviQFvJ9Nv41P0/qqvq1ilNN0PYN2wTqY4mkNvfxMZ0zcL1t9Of/5tEl Tk0v9VZRjV7/g== From: Christian Brauner Subject: [PATCH 0/3] fs: don't warn when a mount is completed from another user namespace Date: Sun, 02 Aug 2026 20:00:42 +0200 Message-Id: <20260802-work-fill_super-warn-v1-0-4e987911a39a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAMqFb2oC/yWM2wrCMBAFf6Xssysx3oK/IiKbuLHRkpZd2wql/ 25jH+dwZiZQlsQKl2oC4SFpavMCu00Foab8ZEyPhcEaezLOWBxbeWNMTXPXvmPBkSQjnSM5ezT WHfawqJ1wTN9/9npbWXv/4vAprfLwpIxeKIe6TEPU7WrM8w87PpWIlAAAAA== X-Change-ID: 20260802-work-fill_super-warn-a7fa82502843 To: Amir Goldstein Cc: Miklos Szeredi , linux-unionfs@vger.kernel.org, Alexander Viro , Jan Kara , Kees Cook , Laurent Vivier , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, "Christian Brauner (Amutable)" , stable@vger.kernel.org X-Mailer: b4 0.16-dev-f2f85 X-Developer-Signature: v=1; a=openpgp-sha256; l=1667; i=brauner@kernel.org; h=from:subject:message-id; bh=yhq9Fu4T1qU5Eg66CKyubI8uMlPD3dDLjZzzlC0UkhM=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWTlt1761vZrmk3uD7czkz4+dJXV/MDXkKflE//Rz9O51 16TYX9NRykLgxgXg6yYIotDu0m43HKeis1GmRowc1iZQIYwcHEKwETCmBkZdoVcDNXWN3jFpjyV 85zCT98J809OuBeeNatA+5bSzDOhhowM16Pb9obpl8W/W5N94PRz7Xs/RJj/ej7Zlz3rIJe2yOL rjAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 123AE18000B X-Stat-Signature: xhif64u6gd4hg86h7xje3dh3a8bw6sfm X-Rspam-User: X-HE-Tag: 1785693655-386414 X-HE-Meta: U2FsdGVkX19gGs0fherQ9zKeow3f47Kggh9VZsQGoLATtzUWWd+vcvJ/GHb0AbyLBueFvu2jMk/kMXVAFQxq3wn5KhlFUGG7rROrtHJtsY2XzOQyIR33LzUD/kMUmmkFiWR/zk3M0TTE8APbFAgX7ROL5dq5zQbdfRihqJS81BPWGTRS92+IS/ZH40eqv4vI2bJ9oLGpBLaOxom4DFwGRRHPLEWXtqv40i8InK1qaqr/bw65/SPrfW82UT4m1VLcbotHlJd2ZTouOAlvCECFAHGrtCYPt0OMZjNIjiD276PjRWHAFva7j7Pn0UKsXRF19iBsPIB1s0YhNITsxTE1O1laU+qWRspVbs1XFpz1d8JpV0LhXQnzi7InlpxdJf9QUlDGnwcCt8cOnLNeyo52DcMy4j2DwDJkTCkxLB+AUl2G3XFwujLSIaMugS+xZnyhTitO/LdajtauQupXt7JvTHRYpSCwPhPHem/4Y5PmMiLwG6lWIQfIqLnfXYrnX3aGl405IktbZYHgRnhn7DITUAsdACSGgtRlrT/dKeDeoXbF6O4gz2AbATT7EU/KvqjmjPqf/gnnvNui/NFBeh+EVj/pz+W9AcwVXyLYCMUR9tqq94ylXyfsHwk9Ur4/7llMiB4aiB5GvV0LjRabRdyktbC7NtsyJVz+YAGxaGiO/pI+dkf+/7/nMWyvL1TtO9hD9lxMJOj3CJG1AALuoDKgXjtvwlLLSLhtGtOTxNKTqn1u88bUgTR3p+zVTq4LnI1eVpp1i39POyd/TZVJEkMzoHSn4AU9EekCJRjsNd/F2ip1mZ5LhyY8Mf9RtqEQKZqeeVZC6gp6AHtekYVsthEPt7ZLhZZw66u5m8LHdVIgEx+/p8k5HDFQ9xyiPEUMamKIAG9IR/+IvpoeQufzny3WlGmJAxIsD5Mqn3nHv3cOK73u4a5nP9VxU/4Gy5Q5y1sSkgUnSJis2I83Fs5gdPG +abK7gA2 dYuEiJLUXQf1WJB0aFIcTYVqAFu/Fw1dGvWzaSJXta8CG4S0Rx8ihRB/yrAwlrtLrFnPNNn+ez0moneSdExzBmbdNMjkW2zc444sx6JaHZg7P13+Ffcsn9lrislMI2K9nYH7w0Stq8tpdceHDg6x5hqlKPOszZOvZQxBwcY4Uh5nQzUYBZV4Vf/VQu7OCo8zuIhOSpxZx29b0rYU2dnKlxz153DBZJejNPSLiCip1IeJMyDz+VeaI+Smy9w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: fsopen() records the caller's user namespace in fc->user_ns and hands back an ordinary file descriptor. The task that calls fsconfig(CMD_CREATE) doesn't have to be the one that created the context, and mount_capable() lets it through as long as the caller has CAP_SYS_ADMIN over fc->user_ns, which anyone in an ancestor namespace does. So fc->user_ns != current_user_ns() is something an unprivileged user can arrange. Both overlayfs and binfmt_misc WARN_ON() that. They're plain WARN_ON()s, so it can be done in a loop to taint the kernel and flood the log, and it panics a machine booted with panic_on_warn. Keep refusing the mount, just stop warning about it. Overlayfs already spells the same check as a plain error return in ovl_parse_param() for Opt_override_creds. And add a selftest for both cases. Signed-off-by: Christian Brauner (Amutable) --- Christian Brauner (3): ovl: don't warn when the mount is completed from another user namespace binfmt_misc: don't warn when the mount is completed from another user namespace selftests/filesystems: test completing a context from another user namespace fs/binfmt_misc.c | 3 +- fs/overlayfs/super.c | 3 +- tools/testing/selftests/Makefile | 1 + .../selftests/filesystems/fscontext_ns/Makefile | 10 + .../filesystems/fscontext_ns/fscontext_ns_test.c | 239 +++++++++++++++++++++ 5 files changed, 254 insertions(+), 2 deletions(-) --- base-commit: c679ce3be6cb63763d68ab9b5d9d73ddc0a40762 change-id: 20260802-work-fill_super-warn-a7fa82502843