* [PATCH] mm: fix use-after-free in sys_remap_file_pages
@ 2013-12-12 22:07 Kees Cook
2013-12-13 3:41 ` Rik van Riel
0 siblings, 1 reply; 5+ messages in thread
From: Kees Cook @ 2013-12-12 22:07 UTC (permalink / raw)
To: linux-kernel
Cc: Andrew Morton, Michel Lespinasse, Rik van Riel, Cyrill Gorcunov,
Hugh Dickins, linux-mm, PaX Team, Dmitry Vyukov
From: PaX Team <pageexec@freemail.hu>
http://lkml.org/lkml/2013/9/17/30
SyS_remap_file_pages() calls mmap_region(), which calls remove_vma_list(),
which calls remove_vma(), which frees the vma. Later (after out label)
SyS_remap_file_pages() accesses the freed vma in vm_flags = vma->vm_flags.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: PaX Team <pageexec@freemail.hu>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
---
mm/fremap.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/fremap.c b/mm/fremap.c
index 5bff08147768..afad07b85ef2 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -218,6 +218,8 @@ get_write_lock:
BUG_ON(addr != start);
err = 0;
}
+ vm_flags = vma->vm_flags;
+ vma = NULL;
goto out;
}
mutex_lock(&mapping->i_mmap_mutex);
--
1.7.9.5
--
Kees Cook
Chrome OS Security
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* Re: [PATCH] mm: fix use-after-free in sys_remap_file_pages
2013-12-12 22:07 [PATCH] mm: fix use-after-free in sys_remap_file_pages Kees Cook
@ 2013-12-13 3:41 ` Rik van Riel
2013-12-13 6:24 ` Cyrill Gorcunov
2013-12-13 11:10 ` PaX Team
0 siblings, 2 replies; 5+ messages in thread
From: Rik van Riel @ 2013-12-13 3:41 UTC (permalink / raw)
To: Kees Cook
Cc: linux-kernel, Andrew Morton, Michel Lespinasse, Cyrill Gorcunov,
Hugh Dickins, linux-mm, PaX Team, Dmitry Vyukov
On Thu, 12 Dec 2013 14:07:57 -0800
Kees Cook <keescook@chromium.org> wrote:
> From: PaX Team <pageexec@freemail.hu>
>
> http://lkml.org/lkml/2013/9/17/30
>
> SyS_remap_file_pages() calls mmap_region(), which calls remove_vma_list(),
> which calls remove_vma(), which frees the vma. Later (after out label)
> SyS_remap_file_pages() accesses the freed vma in vm_flags = vma->vm_flags.
> index 5bff08147768..afad07b85ef2 100644
> --- a/mm/fremap.c
> +++ b/mm/fremap.c
> @@ -218,6 +218,8 @@ get_write_lock:
> BUG_ON(addr != start);
> err = 0;
> }
> + vm_flags = vma->vm_flags;
> + vma = NULL;
> goto out;
If the vma has been freed by the time the code jumps to the
out label (because it was freed by a function called from
mmap_region), surely it will also already have been freed
by the time this patch dereferences it?
Also, setting vma = NULL to avoid the if (vma) branch at
the out: label is unnecessarily obfuscated. Lets make things
clear by documenting what is going on, and having a label
after that dereference.
Maybe something like this patch:
---8<---
Subject: [PATCH] mm: fix use-after-free in sys_remap_file_pages
remap_file_pages calls mmap_region, which may merge the VMA with other existing
VMAs, and free "vma". This can lead to a use-after-free bug. Avoid the bug by
remembering vm_flags before calling mmap_region, and not trying to dereference
vma later.
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
---
mm/fremap.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/fremap.c b/mm/fremap.c
index 87da359..d28ede5 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -203,6 +203,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
if (mapping_cap_account_dirty(mapping)) {
unsigned long addr;
struct file *file = get_file(vma->vm_file);
+ vm_flags = vma->vm_flags;
addr = mmap_region(file, start, size,
vma->vm_flags, pgoff);
@@ -213,7 +214,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
BUG_ON(addr != start);
err = 0;
}
- goto out;
+ /* mmap_region may have freed vma */
+ goto out_freed;
}
mutex_lock(&mapping->i_mmap_mutex);
flush_dcache_mmap_lock(mapping);
@@ -248,6 +250,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
out:
if (vma)
vm_flags = vma->vm_flags;
+out_freed:
if (likely(!has_write_lock))
up_read(&mm->mmap_sem);
else
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^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] mm: fix use-after-free in sys_remap_file_pages
2013-12-13 3:41 ` Rik van Riel
@ 2013-12-13 6:24 ` Cyrill Gorcunov
2013-12-13 11:10 ` PaX Team
1 sibling, 0 replies; 5+ messages in thread
From: Cyrill Gorcunov @ 2013-12-13 6:24 UTC (permalink / raw)
To: Rik van Riel
Cc: Kees Cook, linux-kernel, Andrew Morton, Michel Lespinasse,
Hugh Dickins, linux-mm, PaX Team, Dmitry Vyukov
On Thu, Dec 12, 2013 at 10:41:18PM -0500, Rik van Riel wrote:
>
> If the vma has been freed by the time the code jumps to the
> out label (because it was freed by a function called from
> mmap_region), surely it will also already have been freed
> by the time this patch dereferences it?
>
> Also, setting vma = NULL to avoid the if (vma) branch at
> the out: label is unnecessarily obfuscated. Lets make things
> clear by documenting what is going on, and having a label
> after that dereference.
This patch is a bit easier to read, at least for me. And if
I understand the code flow right, the issue is due to
remap_file_pages -> mmap_region -> find_vma_links -> do_munmap.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] mm: fix use-after-free in sys_remap_file_pages
2013-12-13 3:41 ` Rik van Riel
2013-12-13 6:24 ` Cyrill Gorcunov
@ 2013-12-13 11:10 ` PaX Team
2013-12-13 14:43 ` [PATCH -v2] " Rik van Riel
1 sibling, 1 reply; 5+ messages in thread
From: PaX Team @ 2013-12-13 11:10 UTC (permalink / raw)
To: Kees Cook, Rik van Riel
Cc: linux-kernel, Andrew Morton, Michel Lespinasse, Cyrill Gorcunov,
Hugh Dickins, linux-mm, Dmitry Vyukov
On 12 Dec 2013 at 22:41, Rik van Riel wrote:
> If the vma has been freed by the time the code jumps to the
> out label (because it was freed by a function called from
> mmap_region), surely it will also already have been freed
> by the time this patch dereferences it?
oops, yes, i meant to save the flags away before mmap_region,
no idea how i ended up with this ;).
> Also, setting vma = NULL to avoid the if (vma) branch at
> the out: label is unnecessarily obfuscated. Lets make things
> clear by documenting what is going on, and having a label
> after that dereference.
on that note, how about this as well:
> --- a/mm/fremap.c
> +++ b/mm/fremap.c
> @@ -203,6 +203,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> if (mapping_cap_account_dirty(mapping)) {
> unsigned long addr;
> struct file *file = get_file(vma->vm_file);
> + vm_flags = vma->vm_flags;
>
> addr = mmap_region(file, start, size,
> vma->vm_flags, pgoff);
^^^^^^^^^^^^^
pass in vm_flags instead of vma->vm_flags just to prevent someone
from 'optimizing' away the read in the future?
> @@ -213,7 +214,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> BUG_ON(addr != start);
> err = 0;
> }
> - goto out;
> + /* mmap_region may have freed vma */
> + goto out_freed;
perhaps {copy,move} this comment above the previous hunk since that's
where the relevant action is?
cheers,
PaX Team
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^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH -v2] mm: fix use-after-free in sys_remap_file_pages
2013-12-13 11:10 ` PaX Team
@ 2013-12-13 14:43 ` Rik van Riel
0 siblings, 0 replies; 5+ messages in thread
From: Rik van Riel @ 2013-12-13 14:43 UTC (permalink / raw)
To: pageexec
Cc: Kees Cook, linux-kernel, Andrew Morton, Michel Lespinasse,
Cyrill Gorcunov, Hugh Dickins, linux-mm, Dmitry Vyukov
On Fri, 13 Dec 2013 12:10:17 +0100
"PaX Team" <pageexec@freemail.hu> wrote:
> pass in vm_flags instead of vma->vm_flags just to prevent someone
> from 'optimizing' away the read in the future?
In that case, we should probably also use ACCESS_ONCE, if
only to be explicit about it.
> perhaps {copy,move} this comment above the previous hunk since that's
> where the relevant action is?
See the new version below:
---8<---
Subject: mm: fix use-after-free in sys_remap_file_pages
remap_file_pages calls mmap_region, which may merge the VMA with other existing
VMAs, and free "vma". This can lead to a use-after-free bug. Avoid the bug by
remembering vm_flags before calling mmap_region, and not trying to dereference
vma later.
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
---
mm/fremap.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/mm/fremap.c b/mm/fremap.c
index 87da359..c85e2ec 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -203,9 +203,10 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
if (mapping_cap_account_dirty(mapping)) {
unsigned long addr;
struct file *file = get_file(vma->vm_file);
+ /* mmap_region may free vma; grab the info now */
+ vm_flags = ACCESS_ONCE(vma->vm_flags);
- addr = mmap_region(file, start, size,
- vma->vm_flags, pgoff);
+ addr = mmap_region(file, start, size, vm_flags, pgoff);
fput(file);
if (IS_ERR_VALUE(addr)) {
err = addr;
@@ -213,7 +214,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
BUG_ON(addr != start);
err = 0;
}
- goto out;
+ goto out_freed;
}
mutex_lock(&mapping->i_mmap_mutex);
flush_dcache_mmap_lock(mapping);
@@ -248,6 +249,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
out:
if (vma)
vm_flags = vma->vm_flags;
+out_freed:
if (likely(!has_write_lock))
up_read(&mm->mmap_sem);
else
--
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2013-12-12 22:07 [PATCH] mm: fix use-after-free in sys_remap_file_pages Kees Cook
2013-12-13 3:41 ` Rik van Riel
2013-12-13 6:24 ` Cyrill Gorcunov
2013-12-13 11:10 ` PaX Team
2013-12-13 14:43 ` [PATCH -v2] " Rik van Riel
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