[PATCH] s390/mm: Fix memory leak in add_marker() when kvrealloc fails

[PATCH] s390/mm: Fix memory leak in add_marker() when kvrealloc fails

[Miaoqian Lin]

When kvrealloc() fails, the original markers memory is leaked
because the function directly assigns the NULL to the markers pointer,
losing the reference to the original memory.

As a result, the kvfree() in pt_dump_init() ends up freeing NULL instead
of the previously allocated memory.

Fix this by using a temporary variable to store kvrealloc()'s return
value and only update the markers pointer on success.

Found via static anlaysis and this is similar to commit 42378a9ca553
("bpf, verifier: Fix memory leak in array reallocation for stack state")

Fixes: d0e7915d2ad3 ("s390/mm/ptdump: Generate address marker array dynamically")
Cc: stable@vger.kernel.org
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
---
 arch/s390/mm/dump_pagetables.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c
index 9af2aae0a515..0f2e0c93a1e0 100644
--- a/arch/s390/mm/dump_pagetables.c
+++ b/arch/s390/mm/dump_pagetables.c
@@ -291,16 +291,19 @@ static int ptdump_cmp(const void *a, const void *b)
 
 static int add_marker(unsigned long start, unsigned long end, const char *name)
 {
+	struct addr_marker *new_markers;
 	size_t oldsize, newsize;
 
 	oldsize = markers_cnt * sizeof(*markers);
 	newsize = oldsize + 2 * sizeof(*markers);
 	if (!oldsize)
-		markers = kvmalloc(newsize, GFP_KERNEL);
+		new_markers = kvmalloc(newsize, GFP_KERNEL);
 	else
-		markers = kvrealloc(markers, newsize, GFP_KERNEL);
-	if (!markers)
+		new_markers = kvrealloc(markers, newsize, GFP_KERNEL);
+	if (!new_markers)
 		goto error;
+
+	markers = new_markers;
 	markers[markers_cnt].is_start = 1;
 	markers[markers_cnt].start_address = start;
 	markers[markers_cnt].size = end - start;
-- 
2.39.5 (Apple Git-154)

Re: [PATCH] s390/mm: Fix memory leak in add_marker() when kvrealloc fails

[Heiko Carstens]

On Sun, Oct 26, 2025 at 05:13:51PM +0800, Miaoqian Lin wrote:
> When kvrealloc() fails, the original markers memory is leaked
> because the function directly assigns the NULL to the markers pointer,
> losing the reference to the original memory.
> 
> As a result, the kvfree() in pt_dump_init() ends up freeing NULL instead
> of the previously allocated memory.
> 
> Fix this by using a temporary variable to store kvrealloc()'s return
> value and only update the markers pointer on success.
> 
> Found via static anlaysis and this is similar to commit 42378a9ca553
> ("bpf, verifier: Fix memory leak in array reallocation for stack state")
> 
> Fixes: d0e7915d2ad3 ("s390/mm/ptdump: Generate address marker array dynamically")
> Cc: stable@vger.kernel.org
> Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
> ---
>  arch/s390/mm/dump_pagetables.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c
> index 9af2aae0a515..0f2e0c93a1e0 100644
> --- a/arch/s390/mm/dump_pagetables.c
> +++ b/arch/s390/mm/dump_pagetables.c
> @@ -291,16 +291,19 @@ static int ptdump_cmp(const void *a, const void *b)
>  
>  static int add_marker(unsigned long start, unsigned long end, const char *name)
>  {
> +	struct addr_marker *new_markers;
>  	size_t oldsize, newsize;
>  
>  	oldsize = markers_cnt * sizeof(*markers);
>  	newsize = oldsize + 2 * sizeof(*markers);
>  	if (!oldsize)
> -		markers = kvmalloc(newsize, GFP_KERNEL);
> +		new_markers = kvmalloc(newsize, GFP_KERNEL);
>  	else
> -		markers = kvrealloc(markers, newsize, GFP_KERNEL);
> -	if (!markers)
> +		new_markers = kvrealloc(markers, newsize, GFP_KERNEL);
> +	if (!new_markers)
>  		goto error;
> +
> +	markers = new_markers;

This is not better to the situation before. If the allocation fails,
markers_cnt will be set to zero, but the old valid markers pointer will stay,
which means that the next call to add_marker() will allocate a new area via
kvmalloc() instead of kvrealloc(), and thus leaking the old area too.

add_marker() needs to changes to return in a manner that both marker and
marker_cnt correlate with each other. And I guess it is also easily possible
to get rid of the two different allocation paths.

Care to send a new version?

Re: [PATCH] s390/mm: Fix memory leak in add_marker() when kvrealloc fails

[林妙倩]

Hi, Heiko

Thank you for the feedback.

Heiko Carstens <hca@linux.ibm.com> 于2025年10月27日周一 18:15写道：
>
> On Sun, Oct 26, 2025 at 05:13:51PM +0800, Miaoqian Lin wrote:
> > When kvrealloc() fails, the original markers memory is leaked
> > because the function directly assigns the NULL to the markers pointer,
> > losing the reference to the original memory.
> >
> > As a result, the kvfree() in pt_dump_init() ends up freeing NULL instead
> > of the previously allocated memory.
> >
> > Fix this by using a temporary variable to store kvrealloc()'s return
> > value and only update the markers pointer on success.
> >
> > Found via static anlaysis and this is similar to commit 42378a9ca553
> > ("bpf, verifier: Fix memory leak in array reallocation for stack state")
> >
> > Fixes: d0e7915d2ad3 ("s390/mm/ptdump: Generate address marker array dynamically")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
> > ---
> >  arch/s390/mm/dump_pagetables.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c
> > index 9af2aae0a515..0f2e0c93a1e0 100644
> > --- a/arch/s390/mm/dump_pagetables.c
> > +++ b/arch/s390/mm/dump_pagetables.c
> > @@ -291,16 +291,19 @@ static int ptdump_cmp(const void *a, const void *b)
> >
> >  static int add_marker(unsigned long start, unsigned long end, const char *name)
> >  {
> > +     struct addr_marker *new_markers;
> >       size_t oldsize, newsize;
> >
> >       oldsize = markers_cnt * sizeof(*markers);
> >       newsize = oldsize + 2 * sizeof(*markers);
> >       if (!oldsize)
> > -             markers = kvmalloc(newsize, GFP_KERNEL);
> > +             new_markers = kvmalloc(newsize, GFP_KERNEL);
> >       else
> > -             markers = kvrealloc(markers, newsize, GFP_KERNEL);
> > -     if (!markers)
> > +             new_markers = kvrealloc(markers, newsize, GFP_KERNEL);
> > +     if (!new_markers)
> >               goto error;
> > +
> > +     markers = new_markers;
>
> This is not better to the situation before. If the allocation fails,
> markers_cnt will be set to zero, but the old valid markers pointer will stay,
> which means that the next call to add_marker() will allocate a new area via
> kvmalloc() instead of kvrealloc(), and thus leaking the old area too.
>
> add_marker() needs to changes to return in a manner that both marker and
> marker_cnt correlate with each other. And I guess it is also easily possible
> to get rid of the two different allocation paths.
>
> Care to send a new version?

I'm not sure if I can make it right.
Do you think this way can fix the leak correctly? Thanks.

```diff
static int add_marker(unsigned long start, unsigned long end, const char *name)
 {
-       size_t oldsize, newsize;
-
-       oldsize = markers_cnt * sizeof(*markers);
-       newsize = oldsize + 2 * sizeof(*markers);
-       if (!oldsize)
-               markers = kvmalloc(newsize, GFP_KERNEL);
-       else
-               markers = kvrealloc(markers, newsize, GFP_KERNEL);
-       if (!markers)
-               goto error;
+       struct addr_marker *new_markers;
+       size_t newsize;
+
+       newsize = (markers_cnt + 2) * sizeof(*markers);
+       new_markers = kvrealloc(markers, newsize, GFP_KERNEL);
+       if (!new_markers)
+               return -ENOMEM;
+
+       markers = new_markers;
        markers[markers_cnt].is_start = 1;
        markers[markers_cnt].start_address = start;
        markers[markers_cnt].size = end - start;
@@ -312,9 +311,6 @@ static int add_marker(unsigned long start,
unsigned long end, const char *name)
        markers[markers_cnt].name = name;
        markers_cnt++;
        return 0;
-error:
-       markers_cnt = 0;
-       return -ENOMEM;
 }

Re: [PATCH] s390/mm: Fix memory leak in add_marker() when kvrealloc fails

[Heiko Carstens]

On Mon, Oct 27, 2025 at 07:53:25PM +0800, 林妙倩 wrote:
> > Care to send a new version?
> 
> I'm not sure if I can make it right.
> Do you think this way can fix the leak correctly? Thanks.
> 
> ```diff
> static int add_marker(unsigned long start, unsigned long end, const char *name)
>  {
> -       size_t oldsize, newsize;
> -
> -       oldsize = markers_cnt * sizeof(*markers);
> -       newsize = oldsize + 2 * sizeof(*markers);
> -       if (!oldsize)
> -               markers = kvmalloc(newsize, GFP_KERNEL);
> -       else
> -               markers = kvrealloc(markers, newsize, GFP_KERNEL);
> -       if (!markers)
> -               goto error;
> +       struct addr_marker *new_markers;
> +       size_t newsize;
> +
> +       newsize = (markers_cnt + 2) * sizeof(*markers);
> +       new_markers = kvrealloc(markers, newsize, GFP_KERNEL);
> +       if (!new_markers)
> +               return -ENOMEM;
> +
> +       markers = new_markers;
>         markers[markers_cnt].is_start = 1;
>         markers[markers_cnt].start_address = start;
>         markers[markers_cnt].size = end - start;
> @@ -312,9 +311,6 @@ static int add_marker(unsigned long start,
> unsigned long end, const char *name)
>         markers[markers_cnt].name = name;
>         markers_cnt++;
>         return 0;
> -error:
> -       markers_cnt = 0;
> -       return -ENOMEM;
>  }

Not exactly what I had in mind, but this looks good too.
Could you send a proper second version of your patch, please?

Thanks!