From: Andrew Morton <akpm@linux-foundation.org>
To: willy@infradead.org, vbabka@suse.cz, sumit.semwal@linaro.org,
sashal@kernel.org, pcc@google.com, mhocko@suse.com,
legion@kernel.org, kirill.shutemov@linux.intel.com,
keescook@chromium.org, hannes@cmpxchg.org, gorcunov@gmail.com,
ebiederm@xmission.com, david@redhat.com, dave@stgolabs.net,
dave.hansen@intel.com, chris.hyser@oracle.com, ccross@google.com,
caoxiaofeng@yulong.com, brauner@kernel.org, surenb@google.com,
akpm@linux-foundation.org, patches@lists.linux.dev,
linux-mm@kvack.org, mm-commits@vger.kernel.org,
torvalds@linux-foundation.org, akpm@linux-foundation.org
Subject: [patch 3/8] mm: prevent vm_area_struct::anon_name refcount saturation
Date: Fri, 04 Mar 2022 20:28:55 -0800 [thread overview]
Message-ID: <20220305042855.BFBB9C004E1@smtp.kernel.org> (raw)
In-Reply-To: <20220304202822.d47f8084928321c83070d7d7@linux-foundation.org>
From: Suren Baghdasaryan <surenb@google.com>
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 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
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>
---
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;
_
next prev parent reply other threads:[~2022-03-05 4:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-05 4:28 incoming Andrew Morton
2022-03-05 4:28 ` [patch 1/8] selftests/vm: cleanup hugetlb file after mremap test Andrew Morton
2022-03-05 4:28 ` [patch 2/8] mm: refactor vm_area_struct::anon_vma_name usage code Andrew Morton
2022-03-05 4:28 ` Andrew Morton [this message]
2022-03-05 19:03 ` [patch 3/8] mm: prevent vm_area_struct::anon_name refcount saturation Linus Torvalds
2022-03-05 4:28 ` [patch 4/8] mm: fix use-after-free when anon vma name is used after vma is freed Andrew Morton
2022-03-05 4:29 ` [patch 5/8] memfd: fix F_SEAL_WRITE after shmem huge page allocated Andrew Morton
2022-03-05 4:29 ` [patch 6/8] kselftest/vm: fix tests build with old libc Andrew Morton
2022-03-05 4:29 ` [patch 7/8] proc: fix documentation and description of pagemap Andrew Morton
2022-03-05 4:29 ` [patch 8/8] configs/debug: set CONFIG_DEBUG_INFO=y properly Andrew Morton
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