mm/filemap.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)
Release refcount after xas_set to fix UAF which may cause panic like this:
page:ffffea000491fa40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1247e9
head:ffffea000491fa00 order:3 compound_mapcount:0 compound_pincount:0
memcg:ffff888104f91091
flags: 0x2fffff80010200(slab|head|node=0|zone=2|lastcpupid=0x1fffff)
...
page dumped because: VM_BUG_ON_PAGE(PageTail(page))
------------[ cut here ]------------
kernel BUG at include/linux/page-flags.h:632!
invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
CPU: 1 PID: 7642 Comm: sh Not tainted 5.15.51-dirty #26
...
Call Trace:
<TASK>
__invalidate_mapping_pages+0xe7/0x540
drop_pagecache_sb+0x159/0x320
iterate_supers+0x120/0x240
drop_caches_sysctl_handler+0xaa/0xe0
proc_sys_call_handler+0x2b4/0x480
new_sync_write+0x3d6/0x5c0
vfs_write+0x446/0x7a0
ksys_write+0x105/0x210
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f52b5733130
...
This problem has been fixed on mainline by patch 6b24ca4a1a8d ("mm: Use
multi-index entries in the page cache") since it deletes the related code.
Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
---
mm/filemap.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c
index 00e391e75880..24b5d7ebdc29 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2087,16 +2087,18 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
{
XA_STATE(xas, &mapping->i_pages, start);
struct page *page;
+ bool putpage;
rcu_read_lock();
while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
+ putpage = true;
if (!xa_is_value(page)) {
if (page->index < start)
- goto put;
+ goto next;
if (page->index + thp_nr_pages(page) - 1 > end)
- goto put;
+ goto next;
if (!trylock_page(page))
- goto put;
+ goto next;
if (page->mapping != mapping || PageWriteback(page))
goto unlock;
VM_BUG_ON_PAGE(!thp_contains(page, xas.xa_index),
@@ -2105,20 +2107,24 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
indices[pvec->nr] = xas.xa_index;
if (!pagevec_add(pvec, page))
break;
+ putpage = false;
goto next;
unlock:
unlock_page(page);
-put:
- put_page(page);
next:
if (!xa_is_value(page) && PageTransHuge(page)) {
unsigned int nr_pages = thp_nr_pages(page);
/* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
xas_set(&xas, page->index + nr_pages);
- if (xas.xa_index < nr_pages)
+ if (xas.xa_index < nr_pages) {
+ if (putpage)
+ put_page(page);
break;
+ }
}
+ if (putpage)
+ put_page(page);
}
rcu_read_unlock();
--
2.25.1On Wed, Jul 06, 2022 at 11:24:34AM +0800, Liu Shixin wrote:
> Release refcount after xas_set to fix UAF which may cause panic like this:
I think we can do better. How about this?
diff --git a/mm/filemap.c b/mm/filemap.c
index 00e391e75880..11ae38cc4fd3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2090,7 +2090,9 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
rcu_read_lock();
while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
+ unsigned long next_idx = xas.xa_index + 1;
if (!xa_is_value(page)) {
+ next_idx = page->index + thp_nr_pages(page);
if (page->index < start)
goto put;
if (page->index + thp_nr_pages(page) - 1 > end)
@@ -2111,14 +2113,11 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
put:
put_page(page);
next:
- if (!xa_is_value(page) && PageTransHuge(page)) {
- unsigned int nr_pages = thp_nr_pages(page);
-
- /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
- xas_set(&xas, page->index + nr_pages);
- if (xas.xa_index < nr_pages)
- break;
- }
+ /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
+ if (next_idx < xas.xa_index)
+ break;
+ if (next_idx != xas.xa_index + 1)
+ xas_set(&xas, next_idx);
}
rcu_read_unlock();
On 2022/7/6 11:21, Matthew Wilcox wrote:
> On Wed, Jul 06, 2022 at 11:24:34AM +0800, Liu Shixin wrote:
>> Release refcount after xas_set to fix UAF which may cause panic like this:
> I think we can do better. How about this?
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 00e391e75880..11ae38cc4fd3 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2090,7 +2090,9 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
>
> rcu_read_lock();
> while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
> + unsigned long next_idx = xas.xa_index + 1;
> if (!xa_is_value(page)) {
> + next_idx = page->index + thp_nr_pages(page);
I noticed that there was a VM_BUG_ON_PAGE before which was deleted by patch 6560e8cd869b ("mm/filemap.c: remove bogus VM_BUG_ON")
It seems that page->index and xas.xa_index are not guaranteed to be equal. Therefore, I conservatively retained
the PageTransHuge to keep consistent with the original logic :)
@@ -2090,7 +2090,11 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
rcu_read_lock();
while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
+ unsigned long next_idx = xas.xa_index;
+
if (!xa_is_value(page)) {
+ if (PageTransHuge(page))
+ next_idx = page->index + thp_nr_pages(page);
if (page->index < start)
goto put;
if (page->index + thp_nr_pages(page) - 1 > end)
> if (page->index < start)
> goto put;
> if (page->index + thp_nr_pages(page) - 1 > end)
> @@ -2111,14 +2113,11 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
> put:
> put_page(page);
> next:
> - if (!xa_is_value(page) && PageTransHuge(page)) {
> - unsigned int nr_pages = thp_nr_pages(page);
> -
> - /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
> - xas_set(&xas, page->index + nr_pages);
> - if (xas.xa_index < nr_pages)
> - break;
> - }
> + /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
> + if (next_idx < xas.xa_index)
> + break;
> + if (next_idx != xas.xa_index + 1)
> + xas_set(&xas, next_idx);
> }
> rcu_read_unlock();
>
>
> .
>
On 2022/7/6 11:21, Matthew Wilcox wrote:
> On Wed, Jul 06, 2022 at 11:24:34AM +0800, Liu Shixin wrote:
>> Release refcount after xas_set to fix UAF which may cause panic like this:
> I think we can do better. How about this?
Thank you for your idea, it looks more concise.
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 00e391e75880..11ae38cc4fd3 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2090,7 +2090,9 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
>
> rcu_read_lock();
> while ((page = find_get_entry(&xas, end, XA_PRESENT))) {
> + unsigned long next_idx = xas.xa_index + 1;
> if (!xa_is_value(page)) {
> + next_idx = page->index + thp_nr_pages(page);
> if (page->index < start)
> goto put;
> if (page->index + thp_nr_pages(page) - 1 > end)
> @@ -2111,14 +2113,11 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t start,
> put:
> put_page(page);
> next:
> - if (!xa_is_value(page) && PageTransHuge(page)) {
> - unsigned int nr_pages = thp_nr_pages(page);
> -
> - /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
> - xas_set(&xas, page->index + nr_pages);
> - if (xas.xa_index < nr_pages)
> - break;
> - }
> + /* Final THP may cross MAX_LFS_FILESIZE on 32-bit */
> + if (next_idx < xas.xa_index)
> + break;
> + if (next_idx != xas.xa_index + 1)
> + xas_set(&xas, next_idx);
> }
> rcu_read_unlock();
>
>
> .
>
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