The patch titled
Subject: mm: fix use-after-free when anon vma name is used after vma is freed
has been added to the -mm tree. Its filename is
mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed.patch
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------------------------------------------------------
From: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: mm: fix use-after-free when anon vma name is used after vma is freed
When adjacent vmas are being merged it can result in the vma that was
originally passed to madvise_update_vma being destroyed. In the current
implementation, the name parameter passed to madvise_update_vma points
directly to vma->anon_name->name and it is used after the call to
vma_merge. In the cases when vma_merge merges the original vma and
destroys it, this will result in use-after-free bug as shown below:
madvise_vma_behavior << passes vma->anon_name->name as name param
madvise_update_vma(name)
vma_merge
__vma_adjust
vm_area_free <-- frees the vma
replace_vma_anon_name(name) <-- UAF
Fix this by passing madvise_update_vma a copy of the name.
Link: https://lkml.kernel.org/r/20220210001801.15413-1-surenb@xxxxxxxxxx
Fixes: 9a10064f5625 ("mm: add a field to store names for private anonymous memory")
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reported-by: <syzbot+aa7b3d4b35f9dc46a366@xxxxxxxxxxxxxxxxxxxxxxxxx>
Cc: Colin Cross <ccross@xxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Alexey Gladkov <legion@xxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Chris Hyser <chris.hyser@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Peter Collingbourne <pcc@xxxxxxxxxx>
Cc: Xiaofeng Cao <caoxiaofeng@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 2 ++
kernel/sys.c | 1 -
mm/madvise.c | 14 +++++++++++++-
3 files changed, 15 insertions(+), 2 deletions(-)
--- a/include/linux/mm.h~mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed
+++ a/include/linux/mm.h
@@ -3370,6 +3370,8 @@ static inline int seal_check_future_writ
return 0;
}
+#define ANON_VMA_NAME_MAX_LEN 80
+
#ifdef CONFIG_ANON_VMA_NAME
int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
unsigned long len_in, const char *name);
--- a/kernel/sys.c~mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed
+++ a/kernel/sys.c
@@ -2263,7 +2263,6 @@ int __weak arch_prctl_spec_ctrl_set(stru
#ifdef CONFIG_ANON_VMA_NAME
-#define ANON_VMA_NAME_MAX_LEN 80
#define ANON_VMA_NAME_INVALID_CHARS "\\`$[]"
static inline bool is_valid_name_char(char ch)
--- a/mm/madvise.c~mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed
+++ a/mm/madvise.c
@@ -976,6 +976,8 @@ static int madvise_vma_behavior(struct v
{
int error;
unsigned long new_flags = vma->vm_flags;
+ char name_buf[ANON_VMA_NAME_MAX_LEN];
+ const char *anon_name;
switch (behavior) {
case MADV_REMOVE:
@@ -1040,8 +1042,18 @@ static int madvise_vma_behavior(struct v
break;
}
+ anon_name = vma_anon_name(vma);
+ if (anon_name) {
+ /*
+ * Make a copy of the name because vma might be destroyed when
+ * merged with another one and the name parameter might be used
+ * after that.
+ */
+ strcpy(name_buf, anon_name);
+ anon_name = name_buf;
+ }
error = madvise_update_vma(vma, prev, start, end, new_flags,
- vma_anon_name(vma));
+ anon_name);
out:
/*
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
mm-fix-uaf-when-anon-vma-name-is-used-after-vma-is-freed.patch
