44 lines
1.8 KiB
Diff
44 lines
1.8 KiB
Diff
From 1b24003064570fdf29c55bac14d4728977195133 Mon Sep 17 00:00:00 2001
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From: Aleksa Sarai <cyphar@cyphar.com>
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Date: Fri, 8 Aug 2025 03:55:05 +1000
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Subject: open_tree_attr: do not allow id-mapping changes without
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OPEN_TREE_CLONE
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As described in commit 7a54947e727b ('Merge patch series "fs: allow
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changing idmappings"'), open_tree_attr(2) was necessary in order to
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allow for a detached mount to be created and have its idmappings changed
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without the risk of any racing threads operating on it. For this reason,
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mount_setattr(2) still does not allow for id-mappings to be changed.
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However, there was a bug in commit 2462651ffa76 ("fs: allow changing
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idmappings") which allowed users to bypass this restriction by calling
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open_tree_attr(2) *without* OPEN_TREE_CLONE.
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can_idmap_mount() prevented this bug from allowing an attached
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mountpoint's id-mapping from being modified (thanks to an is_anon_ns()
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check), but this still allows for detached (but visible) mounts to have
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their be id-mapping changed. This risks the same UAF and locking issues
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as described in the merge commit, and was likely unintentional.
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Fixes: 2462651ffa76 ("fs: allow changing idmappings")
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Cc: stable@vger.kernel.org # v6.15+
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Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
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Link: https://lore.kernel.org/20250808-open_tree_attr-bugfix-idmap-v1-1-0ec7bc05646c@cyphar.com
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Signed-off-by: Christian Brauner <brauner@kernel.org>
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---
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fs/namespace.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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--- a/fs/namespace.c
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+++ b/fs/namespace.c
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@@ -5302,7 +5302,8 @@ SYSCALL_DEFINE5(open_tree_attr, int, dfd
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int ret;
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struct mount_kattr kattr = {};
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- kattr.kflags = MOUNT_KATTR_IDMAP_REPLACE;
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+ if (flags & OPEN_TREE_CLONE)
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+ kattr.kflags = MOUNT_KATTR_IDMAP_REPLACE;
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if (flags & AT_RECURSIVE)
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kattr.kflags |= MOUNT_KATTR_RECURSE;
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