From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31E5938399A for ; Tue, 21 Jul 2026 17:13:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784653988; cv=none; b=pGgNWRMvGQHtwWUq3uVOg9C6bgLCSFOFWQynuO3kfNYAP6KIBIvl/iiOX1qWR/55E/cPcPpYAeY3t+R9WRofayI/jtJoAw99xoyKy3LSKm/dv3omxotgQuhsH98hFh4c8HxpRr9YBzfugzSz495n2qBtg1U6sIA2WJz/236WkM8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784653988; c=relaxed/simple; bh=dpWNt6AvLSvXlhXhG6vkLFopcNKY30ZDqXHHCOU9n7k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=r6QYQYQSgR+pNBXmyU4G7cfoAm/dpCBUTWdxdip0Ifc31ZTF5C006IGxbD6Iq7XHa0EwJE2VSV3eugJMjUG8oewzX5EWu07xa+hJRNyOXaUZ6W7BRqdIFtWkTAjhBIgcVnTMWCzZg31691sspC6dCm2V6uV9P3GBkwR7RCAKpdo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=M8plI2oB; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="M8plI2oB" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA61B1F00A3A; Tue, 21 Jul 2026 17:13:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784653987; bh=Ry09ICTEopii93NkzILJAN1L6Yl/Cufz/AIo3v5Fn8Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=M8plI2oBZL5M2ejgZ4jqBjp0Ft6CGBQ6EwnDHxBc0DLPPYF0x/BPd/PEnOkMbOKHP DE/JBfN/ydASBASjODufAmlpQHfB2oQ5z6pPkoq2NPM0RY8wvWlRycn4iImO4m525N eWToH9mVEIuVSqg9tyKbNWfMEb8imcLQczILDXg90TUypNHuMpFC9iLw8q0sEG/PJs 8TNc/yL+AQSBjY36EV9HbvlYKwk8Z1f/sCsBDQfK7hIpQ0yYrY9O86GMDEwoKACaqJ qnlmJkMlkI3Q5wTqkX8DhdB96yzzy0wAX+5tZwDktV3YvceylvYJ5zM9F1OTLBS3In BNrIKVV7NBB6g== From: Sasha Levin To: stable@vger.kernel.org Cc: Pedro Falcato , Jan Kara , "Christian Brauner (Amutable)" , "David Hildenbrand (Arm)" , Al Viro , Jann Horn , "Liam R. Howlett" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Andrew Morton , Sasha Levin Subject: [PATCH 5.15.y] mm: do file ownership checks with the proper mount idmap Date: Tue, 21 Jul 2026 13:13:04 -0400 Message-ID: <20260721171304.107883-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026071536-chirpy-unmindful-fd3a@gregkh> References: <2026071536-chirpy-unmindful-fd3a@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Pedro Falcato [ Upstream commit e187bc02f8fa4226d62814592cf064ee4557c470 ] Ever since idmapped mounts were introduced, inode ownership checks (for side-channel protection) in mincore() and madvise(MADV_PAGEOUT) were done against the nop_mnt_idmap, which completely ignores the file's mount's idmap. This results in odd edgecases like: 1) mount/bind-mount with an idmap userA:userB:1 2) userB runs an owner_or_capable() check on file that is owned by userA on-disk/in-memory, but owned by userB after idmap translation 3) owner_or_capable() mysteriously fails as the correct idmap wasn't supplied In the case of mincore/madvise MADV_PAGEOUT, this is usually benign, because file_permission(file, MAY_WRITE) will probably succeed, as it uses the proper idmap internally, but it does not need to be the case on e.g a 0444 file where even the owner itself doesn't have permissions to write to it. Since this is clearly not trivial to get right, introduce a file_owner_or_capable() that can carry the correct semantics, and switch the various users in mm to it. The issue was found by manual code inspection & an off-list discussion with Jan Kara. Link: https://lore.kernel.org/20260625153853.913949-1-pfalcato@suse.de Fixes: 9caccd41541a ("fs: introduce MOUNT_ATTR_IDMAP") Signed-off-by: Pedro Falcato Reviewed-by: Jan Kara Reviewed-by: Christian Brauner (Amutable) Acked-by: David Hildenbrand (Arm) Cc: Al Viro Cc: Jann Horn Cc: Liam R. Howlett Cc: Matthew Wilcox (Oracle) Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- include/linux/fs.h | 5 +++++ mm/madvise.c | 3 +-- mm/mincore.c | 3 +-- 3 files changed, 7 insertions(+), 4 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 72a956d243c2e8..5b85d4e7321994 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2743,6 +2743,11 @@ static inline struct user_namespace *file_mnt_user_ns(struct file *file) return mnt_user_ns(file->f_path.mnt); } +static inline bool file_owner_or_capable(struct file *file) +{ + return inode_owner_or_capable(file_mnt_user_ns(file), file_inode(file)); +} + /** * is_idmapped_mnt - check whether a mount is mapped * @mnt: the mount to check diff --git a/mm/madvise.c b/mm/madvise.c index ef9382f7762481..367220e1fe52af 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -544,8 +544,7 @@ static inline bool can_do_pageout(struct vm_area_struct *vma) * otherwise we'd be including shared non-exclusive mappings, which * opens a side channel. */ - return inode_owner_or_capable(&init_user_ns, - file_inode(vma->vm_file)) || + return file_owner_or_capable(vma->vm_file) || file_permission(vma->vm_file, MAY_WRITE) == 0; } diff --git a/mm/mincore.c b/mm/mincore.c index 9122676b54d67c..889d84477a7708 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -166,8 +166,7 @@ static inline bool can_do_mincore(struct vm_area_struct *vma) * for writing; otherwise we'd be including shared non-exclusive * mappings, which opens a side channel. */ - return inode_owner_or_capable(&init_user_ns, - file_inode(vma->vm_file)) || + return file_owner_or_capable(vma->vm_file) || file_permission(vma->vm_file, MAY_WRITE) == 0; } -- 2.53.0