| Message ID | 20230617044036.3985524-1-zhiguangni01@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/sparse:avoid null pointer access in memory_present() | expand |
On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@gmail.com> wrote: > __nr_to_section() may return a null pointer, > before accessing the member variable section_mem_map, > we should first determine whether it is a null pointer. > > ... > > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en > set_section_nid(section, nid); > > ms = __nr_to_section(section); > - if (!ms->section_mem_map) { > + if (ms && !ms->section_mem_map) { > ms->section_mem_map = sparse_encode_early_nid(nid) | > SECTION_IS_ONLINE; > __section_mark_present(ms, section); I'm suspecting that if __nr_to_section() returns NULL here, we should just panic. But a null-deref gives the same information, so why change things?
On Sat, 17 Jun 2023 at 13:44, Andrew Morton <akpm@linux-foundation.org> wrote: > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@gmail.com> wrote: > > > __nr_to_section() may return a null pointer, > > before accessing the member variable section_mem_map, > > we should first determine whether it is a null pointer. > > > > ... > > > > --- a/mm/sparse.c > > +++ b/mm/sparse.c > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en > > set_section_nid(section, nid); > > > > ms = __nr_to_section(section); > > - if (!ms->section_mem_map) { > > + if (ms && !ms->section_mem_map) { > > ms->section_mem_map = sparse_encode_early_nid(nid) | > > SECTION_IS_ONLINE; > > __section_mark_present(ms, section); > > I'm suspecting that if __nr_to_section() returns NULL here, we should > just panic. But a null-deref gives the same information, so why change > things? Do you mean if ms is a null pointer，ms->section_mem_map will cause system panic,so we needn't change? >
On Sat, Jun 17, 2023 at 02:17:58PM +0800, Liam Ni wrote: > On Sat, 17 Jun 2023 at 13:44, Andrew Morton <akpm@linux-foundation.org> wrote: > > > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@gmail.com> wrote: > > > > > __nr_to_section() may return a null pointer, > > > before accessing the member variable section_mem_map, > > > we should first determine whether it is a null pointer. > > > > > > ... > > > > > > --- a/mm/sparse.c > > > +++ b/mm/sparse.c > > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en > > > set_section_nid(section, nid); > > > > > > ms = __nr_to_section(section); > > > - if (!ms->section_mem_map) { > > > + if (ms && !ms->section_mem_map) { > > > ms->section_mem_map = sparse_encode_early_nid(nid) | > > > SECTION_IS_ONLINE; > > > __section_mark_present(ms, section); > > > > I'm suspecting that if __nr_to_section() returns NULL here, we should > > just panic. But a null-deref gives the same information, so why change > > things? > > Do you mean if ms is a null pointer，ms->section_mem_map will cause > system panic,so we needn't change? Yes, if __nr_to_section ever returns NULL the system will crash anyway.
On Sat, 17 Jun 2023 at 15:01, Mike Rapoport <rppt@kernel.org> wrote: > > On Sat, Jun 17, 2023 at 02:17:58PM +0800, Liam Ni wrote: > > On Sat, 17 Jun 2023 at 13:44, Andrew Morton <akpm@linux-foundation.org> wrote: > > > > > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@gmail.com> wrote: > > > > > > > __nr_to_section() may return a null pointer, > > > > before accessing the member variable section_mem_map, > > > > we should first determine whether it is a null pointer. > > > > > > > > ... > > > > > > > > --- a/mm/sparse.c > > > > +++ b/mm/sparse.c > > > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en > > > > set_section_nid(section, nid); > > > > > > > > ms = __nr_to_section(section); > > > > - if (!ms->section_mem_map) { > > > > + if (ms && !ms->section_mem_map) { > > > > ms->section_mem_map = sparse_encode_early_nid(nid) | > > > > SECTION_IS_ONLINE; > > > > __section_mark_present(ms, section); > > > > > > I'm suspecting that if __nr_to_section() returns NULL here, we should > > > just panic. But a null-deref gives the same information, so why change > > > things? > > > > Do you mean if ms is a null pointer，ms->section_mem_map will cause > > system panic,so we needn't change? > > Yes, if __nr_to_section ever returns NULL the system will crash anyway. I got it,do we need to print some information by panic()? > > -- > Sincerely yours, > Mike.
On Sat, Jun 17, 2023 at 04:59:46PM +0800, Liam Ni wrote: > On Sat, 17 Jun 2023 at 15:01, Mike Rapoport <rppt@kernel.org> wrote: > > > > On Sat, Jun 17, 2023 at 02:17:58PM +0800, Liam Ni wrote: > > > On Sat, 17 Jun 2023 at 13:44, Andrew Morton <akpm@linux-foundation.org> wrote: > > > > > > > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@gmail.com> wrote: > > > > > > > > > __nr_to_section() may return a null pointer, > > > > > before accessing the member variable section_mem_map, > > > > > we should first determine whether it is a null pointer. > > > > > > > > > > ... > > > > > > > > > > --- a/mm/sparse.c > > > > > +++ b/mm/sparse.c > > > > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en > > > > > set_section_nid(section, nid); > > > > > > > > > > ms = __nr_to_section(section); > > > > > - if (!ms->section_mem_map) { > > > > > + if (ms && !ms->section_mem_map) { > > > > > ms->section_mem_map = sparse_encode_early_nid(nid) | > > > > > SECTION_IS_ONLINE; > > > > > __section_mark_present(ms, section); > > > > > > > > I'm suspecting that if __nr_to_section() returns NULL here, we should > > > > just panic. But a null-deref gives the same information, so why change > > > > things? > > > > > > Do you mean if ms is a null pointer，ms->section_mem_map will cause > > > system panic,so we needn't change? > > > > Yes, if __nr_to_section ever returns NULL the system will crash anyway. > > I got it,do we need to print some information by panic()? Accessing a NULL pointer will cause panic and there will be lots of information spilled into the log anyway.
diff --git a/mm/sparse.c b/mm/sparse.c index 4e6e3a9d49dc..37fa3818bc25 100644 --- a/mm/sparse.c +++ b/mm/sparse.c @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en set_section_nid(section, nid); ms = __nr_to_section(section); - if (!ms->section_mem_map) { + if (ms && !ms->section_mem_map) { ms->section_mem_map = sparse_encode_early_nid(nid) | SECTION_IS_ONLINE; __section_mark_present(ms, section);
__nr_to_section() may return a null pointer, before accessing the member variable section_mem_map, we should first determine whether it is a null pointer. Signed-off-by: Liam Ni <zhiguangni01@gmail.com> --- mm/sparse.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)