* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-02 10:45 [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare() Lorenzo Stoakes
@ 2025-09-02 11:09 ` Christian Brauner
2025-09-02 12:40 ` Lorenzo Stoakes
2025-09-02 13:41 ` Pedro Falcato
` (2 subsequent siblings)
3 siblings, 1 reply; 9+ messages in thread
From: Christian Brauner @ 2025-09-02 11:09 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Andrew Morton, Alexander Viro, Jan Kara, David Hildenbrand,
Liam R . Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Jann Horn, Pedro Falcato,
linux-fsdevel, linux-kernel, linux-mm
On Tue, Sep 02, 2025 at 11:45:33AM +0100, Lorenzo Stoakes wrote:
> In commit bb666b7c2707 ("mm: add mmap_prepare() compatibility layer for
> nested file systems") we introduced the ability for 'nested' drivers and
Fwiw, they're called "stacked filesystems" or "stacking filesystems" such
as overlayfs. I would recommend you use that terminology going forward
so we don't confuse each other.
You've used "nested" here and in the code doc for
compat_vma_mmap_prepare() you used "'wrapper' file systems".
Otherwise seems fine,
Reviewed-by: Christian Brauner <brauner@kernel.org>
> file systems to correctly invoke the f_op->mmap_prepare() handler from an
> f_op->mmap() handler via a compatibility layer implemented in
> compat_vma_mmap_prepare().
>
> This invokes vma_to_desc() to populate vm_area_desc fields according to
> those found in the (not yet fully initialised) VMA passed to f_op->mmap().
>
> However this function implicitly assumes that the struct file which we are
> operating upon is equal to vma->vm_file. This is not a safe assumption in
> all cases.
>
> This is not an issue currently, as so far we have only implemented
> f_op->mmap_prepare() handlers for some file systems and internal mm uses,
> and the only nested f_op->mmap() operations that can be performed upon
> these are those in backing_file_mmap() and coda_file_mmap(), both of which
> use vma->vm_file.
>
> However, moving forward, as we convert drivers to using
> f_op->mmap_prepare(), this will become a problem.
>
> Resolve this issue by explicitly setting desc->file to the provided file
> parameter and update callers accordingly.
>
> We also need to adjust set_vma_from_desc() to account for this fact, and
> only update the vma->vm_file field if the f_op->mmap_prepare() caller
> reassigns it.
>
> We may in future wish to add a new field to struct vm_area_desc to account
> for this 'nested mmap invocation' case, but for now it seems unnecessary.
>
> While we are here, also provide a variant of compat_vma_mmap_prepare() that
> operates against a pointer to any file_operations struct and does not
> assume that the file_operations struct we are interested in is file->f_op.
>
> This function is __compat_vma_mmap_prepare() and we invoke it from
> compat_vma_mmap_prepare() so that we share code between the two functions.
>
> This is important, because some drivers provide hooks in a separate struct,
> for instance struct drm_device provides an fops field for this purpose.
>
> Also update the VMA selftests accordingly.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> ---
> include/linux/fs.h | 2 ++
> mm/util.c | 33 +++++++++++++++++++++++---------
> mm/vma.h | 14 ++++++++++----
> tools/testing/vma/vma_internal.h | 19 +++++++++++-------
> 4 files changed, 48 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7ab4f96d705..3e7160415066 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2279,6 +2279,8 @@ static inline bool can_mmap_file(struct file *file)
> return true;
> }
>
> +int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> + struct file *file, struct vm_area_struct *vma);
> int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma);
>
> static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/mm/util.c b/mm/util.c
> index bb4b47cd6709..83fe15e4483a 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1133,6 +1133,29 @@ void flush_dcache_folio(struct folio *folio)
> EXPORT_SYMBOL(flush_dcache_folio);
> #endif
>
> +/**
> + * __compat_vma_mmap_prepare() - See description for compat_vma_mmap_prepare()
> + * for details. This is the same operation, only with a specific file operations
> + * struct which may or may not be the same as vma->vm_file->f_op.
> + * @f_op - The file operations whose .mmap_prepare() hook is specified.
> + * @vma: The VMA to apply the .mmap_prepare() hook to.
> + * Returns: 0 on success or error.
> + */
> +int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> + struct file *file, struct vm_area_struct *vma)
> +{
> + struct vm_area_desc desc;
> + int err;
> +
> + err = f_op->mmap_prepare(vma_to_desc(vma, file, &desc));
> + if (err)
> + return err;
> + set_vma_from_desc(vma, file, &desc);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(__compat_vma_mmap_prepare);
> +
> /**
> * compat_vma_mmap_prepare() - Apply the file's .mmap_prepare() hook to an
> * existing VMA
> @@ -1161,15 +1184,7 @@ EXPORT_SYMBOL(flush_dcache_folio);
> */
> int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma)
> {
> - struct vm_area_desc desc;
> - int err;
> -
> - err = file->f_op->mmap_prepare(vma_to_desc(vma, &desc));
> - if (err)
> - return err;
> - set_vma_from_desc(vma, &desc);
> -
> - return 0;
> + return __compat_vma_mmap_prepare(file->f_op, file, vma);
> }
> EXPORT_SYMBOL(compat_vma_mmap_prepare);
>
> diff --git a/mm/vma.h b/mm/vma.h
> index bcdc261c5b15..9b21d47ba630 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -230,14 +230,14 @@ static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
> */
>
> static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc)
> + struct file *file, struct vm_area_desc *desc)
> {
> desc->mm = vma->vm_mm;
> desc->start = vma->vm_start;
> desc->end = vma->vm_end;
>
> desc->pgoff = vma->vm_pgoff;
> - desc->file = vma->vm_file;
> + desc->file = file;
> desc->vm_flags = vma->vm_flags;
> desc->page_prot = vma->vm_page_prot;
>
> @@ -248,7 +248,7 @@ static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> }
>
> static inline void set_vma_from_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc)
> + struct file *orig_file, struct vm_area_desc *desc)
> {
> /*
> * Since we're invoking .mmap_prepare() despite having a partially
> @@ -258,7 +258,13 @@ static inline void set_vma_from_desc(struct vm_area_struct *vma,
>
> /* Mutable fields. Populated with initial state. */
> vma->vm_pgoff = desc->pgoff;
> - if (vma->vm_file != desc->file)
> + /*
> + * The desc->file may not be the same as vma->vm_file, but if the
> + * f_op->mmap_prepare() handler is setting this parameter to something
> + * different, it indicates that it wishes the VMA to have its file
> + * assigned to this.
> + */
> + if (orig_file != desc->file && vma->vm_file != desc->file)
> vma_set_file(vma, desc->file);
> if (vma->vm_flags != desc->vm_flags)
> vm_flags_set(vma, desc->vm_flags);
> diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
> index 6f95ec14974f..4ceb4284b6b9 100644
> --- a/tools/testing/vma/vma_internal.h
> +++ b/tools/testing/vma/vma_internal.h
> @@ -1411,25 +1411,30 @@ static inline void free_anon_vma_name(struct vm_area_struct *vma)
>
> /* Declared in vma.h. */
> static inline void set_vma_from_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc);
> -
> + struct file *orig_file, struct vm_area_desc *desc);
> static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc);
> + struct file *file, struct vm_area_desc *desc);
>
> -static int compat_vma_mmap_prepare(struct file *file,
> - struct vm_area_struct *vma)
> +static inline int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> + struct file *file, struct vm_area_struct *vma)
> {
> struct vm_area_desc desc;
> int err;
>
> - err = file->f_op->mmap_prepare(vma_to_desc(vma, &desc));
> + err = f_op->mmap_prepare(vma_to_desc(vma, file, &desc));
> if (err)
> return err;
> - set_vma_from_desc(vma, &desc);
> + set_vma_from_desc(vma, file, &desc);
>
> return 0;
> }
>
> +static inline int compat_vma_mmap_prepare(struct file *file,
> + struct vm_area_struct *vma)
> +{
> + return __compat_vma_mmap_prepare(file->f_op, file, vma);
> +}
> +
> /* Did the driver provide valid mmap hook configuration? */
> static inline bool can_mmap_file(struct file *file)
> {
> --
> 2.50.1
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-02 11:09 ` Christian Brauner
@ 2025-09-02 12:40 ` Lorenzo Stoakes
0 siblings, 0 replies; 9+ messages in thread
From: Lorenzo Stoakes @ 2025-09-02 12:40 UTC (permalink / raw)
To: Christian Brauner
Cc: Andrew Morton, Alexander Viro, Jan Kara, David Hildenbrand,
Liam R . Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Jann Horn, Pedro Falcato,
linux-fsdevel, linux-kernel, linux-mm
On Tue, Sep 02, 2025 at 01:09:57PM +0200, Christian Brauner wrote:
> On Tue, Sep 02, 2025 at 11:45:33AM +0100, Lorenzo Stoakes wrote:
> > In commit bb666b7c2707 ("mm: add mmap_prepare() compatibility layer for
> > nested file systems") we introduced the ability for 'nested' drivers and
>
> Fwiw, they're called "stacked filesystems" or "stacking filesystems" such
> as overlayfs. I would recommend you use that terminology going forward
> so we don't confuse each other.
>
> You've used "nested" here and in the code doc for
> compat_vma_mmap_prepare() you used "'wrapper' file systems".
Thanks, good to know there's a general term (yeah seems even I am not consistent
there :) will fix that up in a separate patch if that's ok.
>
> Otherwise seems fine,
> Reviewed-by: Christian Brauner <brauner@kernel.org>
Thanks!
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-02 10:45 [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare() Lorenzo Stoakes
2025-09-02 11:09 ` Christian Brauner
@ 2025-09-02 13:41 ` Pedro Falcato
2025-09-02 15:08 ` Liam R. Howlett
2025-09-03 5:25 ` kernel test robot
3 siblings, 0 replies; 9+ messages in thread
From: Pedro Falcato @ 2025-09-02 13:41 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Andrew Morton, Alexander Viro, Christian Brauner, Jan Kara,
David Hildenbrand, Liam R . Howlett, Vlastimil Babka,
Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Jann Horn,
linux-fsdevel, linux-kernel, linux-mm
On Tue, Sep 02, 2025 at 11:45:33AM +0100, Lorenzo Stoakes wrote:
> In commit bb666b7c2707 ("mm: add mmap_prepare() compatibility layer for
> nested file systems") we introduced the ability for 'nested' drivers and
> file systems to correctly invoke the f_op->mmap_prepare() handler from an
> f_op->mmap() handler via a compatibility layer implemented in
> compat_vma_mmap_prepare().
>
> This invokes vma_to_desc() to populate vm_area_desc fields according to
> those found in the (not yet fully initialised) VMA passed to f_op->mmap().
>
> However this function implicitly assumes that the struct file which we are
> operating upon is equal to vma->vm_file. This is not a safe assumption in
> all cases.
>
> This is not an issue currently, as so far we have only implemented
> f_op->mmap_prepare() handlers for some file systems and internal mm uses,
> and the only nested f_op->mmap() operations that can be performed upon
> these are those in backing_file_mmap() and coda_file_mmap(), both of which
> use vma->vm_file.
>
> However, moving forward, as we convert drivers to using
> f_op->mmap_prepare(), this will become a problem.
>
> Resolve this issue by explicitly setting desc->file to the provided file
> parameter and update callers accordingly.
>
> We also need to adjust set_vma_from_desc() to account for this fact, and
> only update the vma->vm_file field if the f_op->mmap_prepare() caller
> reassigns it.
>
> We may in future wish to add a new field to struct vm_area_desc to account
> for this 'nested mmap invocation' case, but for now it seems unnecessary.
>
> While we are here, also provide a variant of compat_vma_mmap_prepare() that
> operates against a pointer to any file_operations struct and does not
> assume that the file_operations struct we are interested in is file->f_op.
>
> This function is __compat_vma_mmap_prepare() and we invoke it from
> compat_vma_mmap_prepare() so that we share code between the two functions.
>
> This is important, because some drivers provide hooks in a separate struct,
> for instance struct drm_device provides an fops field for this purpose.
>
> Also update the VMA selftests accordingly.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
LGTM, thanks!
--
Pedro
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-02 10:45 [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare() Lorenzo Stoakes
2025-09-02 11:09 ` Christian Brauner
2025-09-02 13:41 ` Pedro Falcato
@ 2025-09-02 15:08 ` Liam R. Howlett
2025-09-03 14:52 ` Lorenzo Stoakes
2025-09-03 5:25 ` kernel test robot
3 siblings, 1 reply; 9+ messages in thread
From: Liam R. Howlett @ 2025-09-02 15:08 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: Andrew Morton, Alexander Viro, Christian Brauner, Jan Kara,
David Hildenbrand, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Jann Horn, Pedro Falcato,
linux-fsdevel, linux-kernel, linux-mm
* Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [250902 06:46]:
> In commit bb666b7c2707 ("mm: add mmap_prepare() compatibility layer for
> nested file systems") we introduced the ability for 'nested' drivers and
> file systems to correctly invoke the f_op->mmap_prepare() handler from an
> f_op->mmap() handler via a compatibility layer implemented in
> compat_vma_mmap_prepare().
>
> This invokes vma_to_desc() to populate vm_area_desc fields according to
> those found in the (not yet fully initialised) VMA passed to f_op->mmap().
>
> However this function implicitly assumes that the struct file which we are
> operating upon is equal to vma->vm_file. This is not a safe assumption in
> all cases.
>
> This is not an issue currently, as so far we have only implemented
> f_op->mmap_prepare() handlers for some file systems and internal mm uses,
> and the only nested f_op->mmap() operations that can be performed upon
> these are those in backing_file_mmap() and coda_file_mmap(), both of which
> use vma->vm_file.
>
> However, moving forward, as we convert drivers to using
> f_op->mmap_prepare(), this will become a problem.
>
> Resolve this issue by explicitly setting desc->file to the provided file
> parameter and update callers accordingly.
>
> We also need to adjust set_vma_from_desc() to account for this fact, and
> only update the vma->vm_file field if the f_op->mmap_prepare() caller
> reassigns it.
>
> We may in future wish to add a new field to struct vm_area_desc to account
> for this 'nested mmap invocation' case, but for now it seems unnecessary.
>
> While we are here, also provide a variant of compat_vma_mmap_prepare() that
> operates against a pointer to any file_operations struct and does not
> assume that the file_operations struct we are interested in is file->f_op.
>
> This function is __compat_vma_mmap_prepare() and we invoke it from
> compat_vma_mmap_prepare() so that we share code between the two functions.
>
> This is important, because some drivers provide hooks in a separate struct,
> for instance struct drm_device provides an fops field for this purpose.
>
> Also update the VMA selftests accordingly.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
One nit below.
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> ---
> include/linux/fs.h | 2 ++
> mm/util.c | 33 +++++++++++++++++++++++---------
> mm/vma.h | 14 ++++++++++----
> tools/testing/vma/vma_internal.h | 19 +++++++++++-------
> 4 files changed, 48 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7ab4f96d705..3e7160415066 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2279,6 +2279,8 @@ static inline bool can_mmap_file(struct file *file)
> return true;
> }
>
> +int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> + struct file *file, struct vm_area_struct *vma);
> int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma);
>
> static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/mm/util.c b/mm/util.c
> index bb4b47cd6709..83fe15e4483a 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1133,6 +1133,29 @@ void flush_dcache_folio(struct folio *folio)
> EXPORT_SYMBOL(flush_dcache_folio);
> #endif
>
> +/**
> + * __compat_vma_mmap_prepare() - See description for compat_vma_mmap_prepare()
> + * for details. This is the same operation, only with a specific file operations
> + * struct which may or may not be the same as vma->vm_file->f_op.
> + * @f_op - The file operations whose .mmap_prepare() hook is specified.
> + * @vma: The VMA to apply the .mmap_prepare() hook to.
> + * Returns: 0 on success or error.
> + */
> +int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> + struct file *file, struct vm_area_struct *vma)
> +{
> + struct vm_area_desc desc;
> + int err;
> +
> + err = f_op->mmap_prepare(vma_to_desc(vma, file, &desc));
> + if (err)
> + return err;
> + set_vma_from_desc(vma, file, &desc);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(__compat_vma_mmap_prepare);
> +
> /**
> * compat_vma_mmap_prepare() - Apply the file's .mmap_prepare() hook to an
> * existing VMA
> @@ -1161,15 +1184,7 @@ EXPORT_SYMBOL(flush_dcache_folio);
> */
> int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma)
> {
> - struct vm_area_desc desc;
> - int err;
> -
> - err = file->f_op->mmap_prepare(vma_to_desc(vma, &desc));
> - if (err)
> - return err;
> - set_vma_from_desc(vma, &desc);
> -
> - return 0;
> + return __compat_vma_mmap_prepare(file->f_op, file, vma);
> }
> EXPORT_SYMBOL(compat_vma_mmap_prepare);
>
> diff --git a/mm/vma.h b/mm/vma.h
> index bcdc261c5b15..9b21d47ba630 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -230,14 +230,14 @@ static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
> */
>
> static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc)
> + struct file *file, struct vm_area_desc *desc)
> {
> desc->mm = vma->vm_mm;
> desc->start = vma->vm_start;
> desc->end = vma->vm_end;
>
> desc->pgoff = vma->vm_pgoff;
> - desc->file = vma->vm_file;
> + desc->file = file;
> desc->vm_flags = vma->vm_flags;
> desc->page_prot = vma->vm_page_prot;
>
> @@ -248,7 +248,7 @@ static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> }
>
> static inline void set_vma_from_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc)
> + struct file *orig_file, struct vm_area_desc *desc)
> {
> /*
> * Since we're invoking .mmap_prepare() despite having a partially
> @@ -258,7 +258,13 @@ static inline void set_vma_from_desc(struct vm_area_struct *vma,
>
> /* Mutable fields. Populated with initial state. */
> vma->vm_pgoff = desc->pgoff;
> - if (vma->vm_file != desc->file)
> + /*
> + * The desc->file may not be the same as vma->vm_file, but if the
> + * f_op->mmap_prepare() handler is setting this parameter to something
> + * different, it indicates that it wishes the VMA to have its file
> + * assigned to this.
> + */
> + if (orig_file != desc->file && vma->vm_file != desc->file)
> vma_set_file(vma, desc->file);
So now we have to be sure both orig_file and vma->vm_file != desc->file
to set it? This seems to make the function name less accurate.
> if (vma->vm_flags != desc->vm_flags)
> vm_flags_set(vma, desc->vm_flags);
> diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
> index 6f95ec14974f..4ceb4284b6b9 100644
> --- a/tools/testing/vma/vma_internal.h
> +++ b/tools/testing/vma/vma_internal.h
> @@ -1411,25 +1411,30 @@ static inline void free_anon_vma_name(struct vm_area_struct *vma)
>
> /* Declared in vma.h. */
> static inline void set_vma_from_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc);
> -
> + struct file *orig_file, struct vm_area_desc *desc);
> static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> - struct vm_area_desc *desc);
> + struct file *file, struct vm_area_desc *desc);
>
> -static int compat_vma_mmap_prepare(struct file *file,
> - struct vm_area_struct *vma)
> +static inline int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> + struct file *file, struct vm_area_struct *vma)
> {
> struct vm_area_desc desc;
> int err;
>
> - err = file->f_op->mmap_prepare(vma_to_desc(vma, &desc));
> + err = f_op->mmap_prepare(vma_to_desc(vma, file, &desc));
> if (err)
> return err;
> - set_vma_from_desc(vma, &desc);
> + set_vma_from_desc(vma, file, &desc);
>
> return 0;
> }
>
> +static inline int compat_vma_mmap_prepare(struct file *file,
> + struct vm_area_struct *vma)
> +{
> + return __compat_vma_mmap_prepare(file->f_op, file, vma);
> +}
> +
> /* Did the driver provide valid mmap hook configuration? */
> static inline bool can_mmap_file(struct file *file)
> {
> --
> 2.50.1
>
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-02 15:08 ` Liam R. Howlett
@ 2025-09-03 14:52 ` Lorenzo Stoakes
2025-09-03 15:08 ` Lorenzo Stoakes
0 siblings, 1 reply; 9+ messages in thread
From: Lorenzo Stoakes @ 2025-09-03 14:52 UTC (permalink / raw)
To: Liam R. Howlett, Andrew Morton, Alexander Viro, Christian Brauner,
Jan Kara, David Hildenbrand, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Jann Horn, Pedro Falcato,
linux-fsdevel, linux-kernel, linux-mm
On Tue, Sep 02, 2025 at 11:08:10AM -0400, Liam R. Howlett wrote:
>
> One nit below.
>
> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Thanks!
>
> > ---
> > include/linux/fs.h | 2 ++
> > mm/util.c | 33 +++++++++++++++++++++++---------
> > mm/vma.h | 14 ++++++++++----
> > tools/testing/vma/vma_internal.h | 19 +++++++++++-------
> > 4 files changed, 48 insertions(+), 20 deletions(-)
> >
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index d7ab4f96d705..3e7160415066 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -2279,6 +2279,8 @@ static inline bool can_mmap_file(struct file *file)
> > return true;
> > }
> >
> > +int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> > + struct file *file, struct vm_area_struct *vma);
> > int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma);
> >
> > static inline int vfs_mmap(struct file *file, struct vm_area_struct *vma)
> > diff --git a/mm/util.c b/mm/util.c
> > index bb4b47cd6709..83fe15e4483a 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -1133,6 +1133,29 @@ void flush_dcache_folio(struct folio *folio)
> > EXPORT_SYMBOL(flush_dcache_folio);
> > #endif
> >
> > +/**
> > + * __compat_vma_mmap_prepare() - See description for compat_vma_mmap_prepare()
> > + * for details. This is the same operation, only with a specific file operations
> > + * struct which may or may not be the same as vma->vm_file->f_op.
> > + * @f_op - The file operations whose .mmap_prepare() hook is specified.
> > + * @vma: The VMA to apply the .mmap_prepare() hook to.
> > + * Returns: 0 on success or error.
> > + */
> > +int __compat_vma_mmap_prepare(const struct file_operations *f_op,
> > + struct file *file, struct vm_area_struct *vma)
> > +{
> > + struct vm_area_desc desc;
> > + int err;
> > +
> > + err = f_op->mmap_prepare(vma_to_desc(vma, file, &desc));
> > + if (err)
> > + return err;
> > + set_vma_from_desc(vma, file, &desc);
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL(__compat_vma_mmap_prepare);
> > +
> > /**
> > * compat_vma_mmap_prepare() - Apply the file's .mmap_prepare() hook to an
> > * existing VMA
> > @@ -1161,15 +1184,7 @@ EXPORT_SYMBOL(flush_dcache_folio);
> > */
> > int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma)
> > {
> > - struct vm_area_desc desc;
> > - int err;
> > -
> > - err = file->f_op->mmap_prepare(vma_to_desc(vma, &desc));
> > - if (err)
> > - return err;
> > - set_vma_from_desc(vma, &desc);
> > -
> > - return 0;
> > + return __compat_vma_mmap_prepare(file->f_op, file, vma);
> > }
> > EXPORT_SYMBOL(compat_vma_mmap_prepare);
> >
> > diff --git a/mm/vma.h b/mm/vma.h
> > index bcdc261c5b15..9b21d47ba630 100644
> > --- a/mm/vma.h
> > +++ b/mm/vma.h
> > @@ -230,14 +230,14 @@ static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
> > */
> >
> > static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> > - struct vm_area_desc *desc)
> > + struct file *file, struct vm_area_desc *desc)
> > {
> > desc->mm = vma->vm_mm;
> > desc->start = vma->vm_start;
> > desc->end = vma->vm_end;
> >
> > desc->pgoff = vma->vm_pgoff;
> > - desc->file = vma->vm_file;
> > + desc->file = file;
> > desc->vm_flags = vma->vm_flags;
> > desc->page_prot = vma->vm_page_prot;
> >
> > @@ -248,7 +248,7 @@ static inline struct vm_area_desc *vma_to_desc(struct vm_area_struct *vma,
> > }
> >
> > static inline void set_vma_from_desc(struct vm_area_struct *vma,
> > - struct vm_area_desc *desc)
> > + struct file *orig_file, struct vm_area_desc *desc)
> > {
> > /*
> > * Since we're invoking .mmap_prepare() despite having a partially
> > @@ -258,7 +258,13 @@ static inline void set_vma_from_desc(struct vm_area_struct *vma,
> >
> > /* Mutable fields. Populated with initial state. */
> > vma->vm_pgoff = desc->pgoff;
> > - if (vma->vm_file != desc->file)
> > + /*
> > + * The desc->file may not be the same as vma->vm_file, but if the
> > + * f_op->mmap_prepare() handler is setting this parameter to something
> > + * different, it indicates that it wishes the VMA to have its file
> > + * assigned to this.
> > + */
> > + if (orig_file != desc->file && vma->vm_file != desc->file)
> > vma_set_file(vma, desc->file);
>
> So now we have to be sure both orig_file and vma->vm_file != desc->file
> to set it? This seems to make the function name less accurate.
I'll update the comment accordingly.
On this in general - In future an mmap_prepare() caller may wish to change
the file to desc->file from vma->vm_file which currently won't work for a
stacked file system.
It's pretty niche and unlikely anybody does it, but if they do, since I am
the one implementing all this I will adjust the descriptor to send a
separate file parameter and adjust this code accordingly.
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-03 14:52 ` Lorenzo Stoakes
@ 2025-09-03 15:08 ` Lorenzo Stoakes
0 siblings, 0 replies; 9+ messages in thread
From: Lorenzo Stoakes @ 2025-09-03 15:08 UTC (permalink / raw)
To: Liam R. Howlett, Andrew Morton, Alexander Viro, Christian Brauner,
Jan Kara, David Hildenbrand, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Jann Horn, Pedro Falcato,
linux-fsdevel, linux-kernel, linux-mm
On Wed, Sep 03, 2025 at 03:52:21PM +0100, Lorenzo Stoakes wrote:
> On Tue, Sep 02, 2025 at 11:08:10AM -0400, Liam R. Howlett wrote:
> >
> > One nit below.
> > > static inline void set_vma_from_desc(struct vm_area_struct *vma,
> > > - struct vm_area_desc *desc)
> > > + struct file *orig_file, struct vm_area_desc *desc)
> > > {
> > > /*
> > > * Since we're invoking .mmap_prepare() despite having a partially
> > > @@ -258,7 +258,13 @@ static inline void set_vma_from_desc(struct vm_area_struct *vma,
> > >
> > > /* Mutable fields. Populated with initial state. */
> > > vma->vm_pgoff = desc->pgoff;
> > > - if (vma->vm_file != desc->file)
> > > + /*
> > > + * The desc->file may not be the same as vma->vm_file, but if the
> > > + * f_op->mmap_prepare() handler is setting this parameter to something
> > > + * different, it indicates that it wishes the VMA to have its file
> > > + * assigned to this.
> > > + */
> > > + if (orig_file != desc->file && vma->vm_file != desc->file)
> > > vma_set_file(vma, desc->file);
> >
> > So now we have to be sure both orig_file and vma->vm_file != desc->file
> > to set it? This seems to make the function name less accurate.
>
> I'll update the comment accordingly.
>
> On this in general - In future an mmap_prepare() caller may wish to change
> the file to desc->file from vma->vm_file which currently won't work for a
> stacked file system.
>
> It's pretty niche and unlikely anybody does it, but if they do, since I am
> the one implementing all this I will adjust the descriptor to send a
> separate file parameter and adjust this code accordingly.
>
> Cheers, Lorenzo
Actually, let me also send vma->vm_file in desc and make that what gets updated,
and make struct file read-only.
That way we solve this problem a lot more neatly. No users are currently setting
desc->file so it's safe to do right now.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-02 10:45 [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare() Lorenzo Stoakes
` (2 preceding siblings ...)
2025-09-02 15:08 ` Liam R. Howlett
@ 2025-09-03 5:25 ` kernel test robot
2025-09-03 17:35 ` Lorenzo Stoakes
3 siblings, 1 reply; 9+ messages in thread
From: kernel test robot @ 2025-09-03 5:25 UTC (permalink / raw)
To: Lorenzo Stoakes, Andrew Morton
Cc: oe-kbuild-all, Linux Memory Management List, Alexander Viro,
Christian Brauner, Jan Kara, David Hildenbrand, Liam R . Howlett,
Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko,
Jann Horn, Pedro Falcato, linux-fsdevel, linux-kernel
Hi Lorenzo,
kernel test robot noticed the following build warnings:
[auto build test WARNING on akpm-mm/mm-everything]
url: https://github.com/intel-lab-lkp/linux/commits/Lorenzo-Stoakes/mm-do-not-assume-file-vma-vm_file-in-compat_vma_mmap_prepare/20250902-184946
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20250902104533.222730-1-lorenzo.stoakes%40oracle.com
patch subject: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
config: i386-buildonly-randconfig-001-20250903 (https://download.01.org/0day-ci/archive/20250903/202509031346.N6FpuQIA-lkp@intel.com/config)
compiler: gcc-13 (Debian 13.3.0-16) 13.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250903/202509031346.N6FpuQIA-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509031346.N6FpuQIA-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> Warning: mm/util.c:1145 function parameter 'f_op' not described in '__compat_vma_mmap_prepare'
>> Warning: mm/util.c:1145 function parameter 'file' not described in '__compat_vma_mmap_prepare'
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
2025-09-03 5:25 ` kernel test robot
@ 2025-09-03 17:35 ` Lorenzo Stoakes
0 siblings, 0 replies; 9+ messages in thread
From: Lorenzo Stoakes @ 2025-09-03 17:35 UTC (permalink / raw)
To: kernel test robot
Cc: Andrew Morton, oe-kbuild-all, Linux Memory Management List,
Alexander Viro, Christian Brauner, Jan Kara, David Hildenbrand,
Liam R . Howlett, Vlastimil Babka, Mike Rapoport,
Suren Baghdasaryan, Michal Hocko, Jann Horn, Pedro Falcato,
linux-fsdevel, linux-kernel
On Wed, Sep 03, 2025 at 01:25:47PM +0800, kernel test robot wrote:
> Hi Lorenzo,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on akpm-mm/mm-everything]
>
> url: https://github.com/intel-lab-lkp/linux/commits/Lorenzo-Stoakes/mm-do-not-assume-file-vma-vm_file-in-compat_vma_mmap_prepare/20250902-184946
> base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link: https://lore.kernel.org/r/20250902104533.222730-1-lorenzo.stoakes%40oracle.com
> patch subject: [PATCH] mm: do not assume file == vma->vm_file in compat_vma_mmap_prepare()
> config: i386-buildonly-randconfig-001-20250903 (https://download.01.org/0day-ci/archive/20250903/202509031346.N6FpuQIA-lkp@intel.com/config)
> compiler: gcc-13 (Debian 13.3.0-16) 13.3.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250903/202509031346.N6FpuQIA-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202509031346.N6FpuQIA-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
> >> Warning: mm/util.c:1145 function parameter 'f_op' not described in '__compat_vma_mmap_prepare'
This is because I used '-' and not ':' :)
> >> Warning: mm/util.c:1145 function parameter 'file' not described in '__compat_vma_mmap_prepare'
And this I just missed adding.
Both are fixed in respin I am about to send.
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 9+ messages in thread