The patch below does not apply to the 5.16-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 96403e11283def1d1c465c8279514c9a504d8630 Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan surenb@google.com Date: Fri, 4 Mar 2022 20:28:55 -0800 Subject: [PATCH] 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 and freeze the ref counter. This would lead to the refcounted object never being freed. A determined attacker could leak memory like that but it would be rather expensive and inefficient way to do so.
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@google.com Signed-off-by: Suren Baghdasaryan surenb@google.com Suggested-by: Michal Hocko mhocko@suse.com Acked-by: Michal Hocko mhocko@suse.com Cc: Alexey Gladkov legion@kernel.org Cc: Chris Hyser chris.hyser@oracle.com Cc: Christian Brauner brauner@kernel.org Cc: Colin Cross ccross@google.com Cc: Cyrill Gorcunov gorcunov@gmail.com Cc: Dave Hansen dave.hansen@intel.com Cc: David Hildenbrand david@redhat.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: "Eric W. Biederman" ebiederm@xmission.com Cc: Johannes Weiner hannes@cmpxchg.org Cc: Kees Cook keescook@chromium.org Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Cc: Matthew Wilcox willy@infradead.org Cc: Peter Collingbourne pcc@google.com Cc: Sasha Levin sashal@kernel.org Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Vlastimil Babka vbabka@suse.cz Cc: Xiaofeng Cao caoxiaofeng@yulong.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index dd3accaa4e6d..cf90b1fa2c60 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -161,15 +161,25 @@ static inline void anon_vma_name_put(struct anon_vma_name *anon_name) 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) diff --git a/mm/madvise.c b/mm/madvise.c index 081b1cded21e..1f2693dccf7b 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -113,8 +113,7 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, 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;