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Patch series "mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()", v2. As part of the efforts to eliminate the problematic f_op->mmap callback, a new callback - f_op->mmap_prepare was provided. While we are converting these callbacks, we must deal with 'stacked' filesystems and drivers - those which in their own f_op->mmap callback invoke an inner f_op->mmap callback. To accomodate for this, a compatibility layer is provided that, via vfs_mmap(), detects if f_op->mmap_prepare is provided and if so, generates a vm_area_desc containing the VMA's metadata and invokes the call. So far, we have provided desc->file equal to vma->vm_file. However this is not necessarily valid, especially in the case of stacked drivers which wish to assign a new file after the inner hook is invoked. To account for this, we adjust vm_area_desc to have both file and vm_file fields. The .vm_file field is strictly set to vma->vm_file (or in the case of a new mapping, what will become vma->vm_file). However, .file is set to whichever file vfs_mmap() is invoked with when using the compatibilty layer. Therefore, if the VMA's file needs to be updated in .mmap_prepare, desc->vm_file should be assigned, whilst desc->file should be read. No current f_op->mmap_prepare users assign desc->file so this is safe to do. This makes the .mmap_prepare callback in the context of a stacked filesystem or driver completely consistent with the existing .mmap implementations. While we're here, we do a few small cleanups, and ensure that we const-ify things correctly in the vm_area_desc struct to avoid hooks accidentally trying to assign fields they should not. This patch (of 2): Stacked filesystems and drivers may invoke mmap hooks with a struct file pointer that differs from the overlying file. We will make this functionality possible in a subsequent patch. In order to prepare for this, let's update vm_area_struct to separately provide desc->file and desc->vm_file parameters. The desc->file parameter is the file that the hook is expected to operate upon, and is not assignable (though the hok may wish to e.g. update the file's accessed time for instance). The desc->vm_file defaults to what will become vma->vm_file and is what the hook must reassign should it wish to change the VMA"s vma->vm_file. For now we keep desc->file, vm_file the same to remain consistent. No f_op->mmap_prepare() callback sets a new vma->vm_file currently, so this is safe to change. While we're here, make the mm_struct desc->mm pointers at immutable as well as the desc->mm field itself. As part of this change, also update the single hook which this would otherwise break - mlock_future_ok(), invoked by secretmem_mmap_prepare()). We additionally update set_vma_from_desc() to compare fields in a more logical fashion, checking the (possibly) user-modified fields as the first operand against the existing value as the second one. Additionally, update VMA tests to accommodate changes. Link: https://lkml.kernel.org/r/cover.1756920635.git.lorenzo.stoakes@oracle.com Link: https://lkml.kernel.org/r/3fa15a861bb7419f033d22970598aa61850ea267.1756920635.git.lorenzo.stoakes@oracle.com Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <brauner@kernel.org> Cc: David Hildenbrand <david@redhat.com> Cc: Jan Kara <jack@suse.cz> Cc: Jann Horn <jannh@google.com> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Pedro Falcato <pfalcato@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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