The patch titled
Subject: mm: prevent vm_area_struct::anon_name refcount saturation
has been added to the -mm tree. Its filename is
mm-prevent-vm_area_struct-anon_name-refcount-saturation.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-prevent-vm_area_struct-anon_name-refcount-saturation.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-prevent-vm_area_struct-anon_name-refcount-saturation.patch
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------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: mm: prevent vm_area_struct::anon_name refcount saturation
A deep process chain with many vmas could grow really high. With default
sysctl_max_map_count (64k) and default pid_max (32k) the max number of
vmas in the system is 2147450880 and the refcounter has headroom of
1073774592 before it reaches REFCOUNT_SATURATED (3221225472).
Therefore it's unlikely that an anonymous name refcounter will overflow
with these defaults. Currently the max for pid_max is PID_MAX_LIMIT
(4194304) and for sysctl_max_map_count it's INT_MAX (2147483647). In this
configuration anon_vma_name refcount overflow becomes theoretically
possible (that still require heavy sharing of that anon_vma_name between
processes).
kref refcounting interface used in anon_vma_name structure will detect a
counter overflow when it reaches REFCOUNT_SATURATED value but will only
generate a warning about broken refcounter.
To ensure anon_vma_name refcount does not overflow, stop anon_vma_name
sharing when the refcount reaches REFCOUNT_MAX (2147483647), which still
leaves INT_MAX/2 (1073741823) values before the counter reaches
REFCOUNT_SATURATED. This should provide enough headroom for raising the
refcounts temporarily.
Link: https://lkml.kernel.org/r/20220223153613.835563-2-surenb@xxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Alexey Gladkov <legion@xxxxxxxxxx>
Cc: Chris Hyser <chris.hyser@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Xiaofeng Cao <caoxiaofeng@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm_inline.h | 18 ++++++++++++++----
mm/madvise.c | 3 +--
2 files changed, 15 insertions(+), 6 deletions(-)
--- a/include/linux/mm_inline.h~mm-prevent-vm_area_struct-anon_name-refcount-saturation
+++ a/include/linux/mm_inline.h
@@ -161,15 +161,25 @@ static inline void anon_vma_name_put(str
kref_put(&anon_name->kref, anon_vma_name_free);
}
+static inline
+struct anon_vma_name *anon_vma_name_reuse(struct anon_vma_name *anon_name)
+{
+ /* Prevent anon_name refcount saturation early on */
+ if (kref_read(&anon_name->kref) < REFCOUNT_MAX) {
+ anon_vma_name_get(anon_name);
+ return anon_name;
+
+ }
+ return anon_vma_name_alloc(anon_name->name);
+}
+
static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
struct vm_area_struct *new_vma)
{
struct anon_vma_name *anon_name = anon_vma_name(orig_vma);
- if (anon_name) {
- anon_vma_name_get(anon_name);
- new_vma->anon_name = anon_name;
- }
+ if (anon_name)
+ new_vma->anon_name = anon_vma_name_reuse(anon_name);
}
static inline void free_anon_vma_name(struct vm_area_struct *vma)
--- a/mm/madvise.c~mm-prevent-vm_area_struct-anon_name-refcount-saturation
+++ a/mm/madvise.c
@@ -113,8 +113,7 @@ static int replace_anon_vma_name(struct
if (anon_vma_name_eq(orig_name, anon_name))
return 0;
- anon_vma_name_get(anon_name);
- vma->anon_name = anon_name;
+ vma->anon_name = anon_vma_name_reuse(anon_name);
anon_vma_name_put(orig_name);
return 0;
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
mm-fix-use-after-free-bug-when-mm-mmap-is-reused-after-being-freed.patch
mm-refactor-vm_area_struct-anon_vma_name-usage-code.patch
mm-prevent-vm_area_struct-anon_name-refcount-saturation.patch
mm-fix-use-after-free-when-anon-vma-name-is-used-after-vma-is-freed.patch
mm-count-time-in-drain_all_pages-during-direct-reclaim-as-memory-pressure.patch
