[PATCH v2] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[PATCH v2] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[Yihao Wu]

Deleting list entry within hlist_for_each_entry_safe is not safe unless
next pointer (tmp) is protected too. It's not, because once hash_lock
is released, cache_clean may delete the entry that tmp points to. Then
cache_purge can walk to a deleted entry and tries to double free it.

Fix this bug by holding only the deleted entry's reference.

Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
---
 net/sunrpc/cache.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index af0ddd28b081..9649c7fcccd2 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -541,7 +541,8 @@ void cache_purge(struct cache_detail *detail)
 	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
 	for (i = 0; i < detail->hash_size; i++) {
 		head = &detail->hash_table[i];
-		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
+		while (!hlist_empty(head)) {
+			ch = hlist_entry(head->first, struct cache_head, cache_list);
 			sunrpc_begin_cache_remove_entry(ch, detail);
 			spin_unlock(&detail->hash_lock);
 			sunrpc_end_cache_remove_entry(ch, detail);
-- 
2.20.1.2432.ga663e714

[PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[Yihao Wu]

Deleting list entry within hlist_for_each_entry_safe is not safe unless
next pointer (tmp) is protected too. It's not, because once hash_lock
is released, cache_clean may delete the entry that tmp points to. Then
cache_purge can walk to a deleted entry and tries to double free it.

Fix this bug by holding only the deleted entry's reference.

Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
---
v1->v2: Use Neil's better solution
v2->v3: Fix a checkscript warning

 net/sunrpc/cache.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index af0ddd28b081..b445874e8e2f 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -541,7 +541,9 @@ void cache_purge(struct cache_detail *detail)
 	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
 	for (i = 0; i < detail->hash_size; i++) {
 		head = &detail->hash_table[i];
-		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
+		while (!hlist_empty(head)) {
+			ch = hlist_entry(head->first, struct cache_head,
+					 cache_list);
 			sunrpc_begin_cache_remove_entry(ch, detail);
 			spin_unlock(&detail->hash_lock);
 			sunrpc_end_cache_remove_entry(ch, detail);
-- 
2.20.1.2432.ga663e714

Re: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[Chuck Lever]

Hi Yihao-

> On Apr 5, 2020, at 1:57 PM, Yihao Wu <wuyihao@linux.alibaba.com> wrote:
> 
> Deleting list entry within hlist_for_each_entry_safe is not safe unless
> next pointer (tmp) is protected too. It's not, because once hash_lock
> is released, cache_clean may delete the entry that tmp points to. Then
> cache_purge can walk to a deleted entry and tries to double free it.
> 
> Fix this bug by holding only the deleted entry's reference.
> 
> Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
> ---
> v1->v2: Use Neil's better solution
> v2->v3: Fix a checkscript warning
> 
> net/sunrpc/cache.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index af0ddd28b081..b445874e8e2f 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -541,7 +541,9 @@ void cache_purge(struct cache_detail *detail)
> 	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
> 	for (i = 0; i < detail->hash_size; i++) {
> 		head = &detail->hash_table[i];
> -		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {

If review/testing shows you need to respin this patch, I note that "tmp" is
now unused and should be removed. I've pulled v3 into my testing branch and
made that minor change. Thanks!


> +		while (!hlist_empty(head)) {
> +			ch = hlist_entry(head->first, struct cache_head,
> +					 cache_list);
> 			sunrpc_begin_cache_remove_entry(ch, detail);
> 			spin_unlock(&detail->hash_lock);
> 			sunrpc_end_cache_remove_entry(ch, detail);
> -- 
> 2.20.1.2432.ga663e714

--
Chuck Lever

Re: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[Yihao Wu]

>> net/sunrpc/cache.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
>> index af0ddd28b081..b445874e8e2f 100644
>> --- a/net/sunrpc/cache.c
>> +++ b/net/sunrpc/cache.c
>> @@ -541,7 +541,9 @@ void cache_purge(struct cache_detail *detail)
>> 	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
>> 	for (i = 0; i < detail->hash_size; i++) {
>> 		head = &detail->hash_table[i];
>> -		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
> 
> If review/testing shows you need to respin this patch, I note that "tmp" is
> now unused and should be removed. I've pulled v3 into my testing branch and
> made that minor change. Thanks!
> 
> 
>> +		while (!hlist_empty(head)) {
>> +			ch = hlist_entry(head->first, struct cache_head,
>> +					 cache_list);
>> 			sunrpc_begin_cache_remove_entry(ch, detail);
>> 			spin_unlock(&detail->hash_lock);
>> 			sunrpc_end_cache_remove_entry(ch, detail);
>> -- 
>> 2.20.1.2432.ga663e714
> 
> --
> Chuck Lever
> 
> 

Thanks a lot, Chuck!

If it needs further changes by me, I'll fix the unused 'tmp' along with them.

BTW, if you and Neil think it's proper to add Signed-off-by Neil too later,
please do, since the bug fix owes to Neil's idea :-)

Yihao Wu

Re: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[Chuck Lever]

> On Apr 5, 2020, at 2:31 PM, Yihao Wu <wuyihao@linux.alibaba.com> wrote:
> 
>>> net/sunrpc/cache.c | 4 +++-
>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
>>> index af0ddd28b081..b445874e8e2f 100644
>>> --- a/net/sunrpc/cache.c
>>> +++ b/net/sunrpc/cache.c
>>> @@ -541,7 +541,9 @@ void cache_purge(struct cache_detail *detail)
>>> 	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
>>> 	for (i = 0; i < detail->hash_size; i++) {
>>> 		head = &detail->hash_table[i];
>>> -		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
>> 
>> If review/testing shows you need to respin this patch, I note that "tmp" is
>> now unused and should be removed. I've pulled v3 into my testing branch and
>> made that minor change. Thanks!
>> 
>> 
>>> +		while (!hlist_empty(head)) {
>>> +			ch = hlist_entry(head->first, struct cache_head,
>>> +					 cache_list);
>>> 			sunrpc_begin_cache_remove_entry(ch, detail);
>>> 			spin_unlock(&detail->hash_lock);
>>> 			sunrpc_end_cache_remove_entry(ch, detail);
>>> -- 
>>> 2.20.1.2432.ga663e714
>> 
>> --
>> Chuck Lever
>> 
>> 
> 
> Thanks a lot, Chuck!
> 
> If it needs further changes by me, I'll fix the unused 'tmp' along with them.
> 
> BTW, if you and Neil think it's proper to add Signed-off-by Neil too later,
> please do, since the bug fix owes to Neil's idea :-)

Actually a "Suggested-by:" tag is appropriate for attribution. I'll add:

Suggested-by: NeilBrown <neilb@suse.de>

to what I have in my tree.


--
Chuck Lever

Re: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

[NeilBrown]

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On Mon, Apr 06 2020, Yihao Wu wrote:

> Deleting list entry within hlist_for_each_entry_safe is not safe unless
> next pointer (tmp) is protected too. It's not, because once hash_lock
> is released, cache_clean may delete the entry that tmp points to. Then
> cache_purge can walk to a deleted entry and tries to double free it.
>
> Fix this bug by holding only the deleted entry's reference.
>
> Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
> ---
> v1->v2: Use Neil's better solution
> v2->v3: Fix a checkscript warning
>
>  net/sunrpc/cache.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index af0ddd28b081..b445874e8e2f 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -541,7 +541,9 @@ void cache_purge(struct cache_detail *detail)
>  	dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
>  	for (i = 0; i < detail->hash_size; i++) {
>  		head = &detail->hash_table[i];
> -		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
> +		while (!hlist_empty(head)) {
> +			ch = hlist_entry(head->first, struct cache_head,
> +					 cache_list);
>  			sunrpc_begin_cache_remove_entry(ch, detail);
>  			spin_unlock(&detail->hash_lock);
>  			sunrpc_end_cache_remove_entry(ch, detail);
> -- 
> 2.20.1.2432.ga663e714

Reviewed-by: NeilBrown <neilb@suse.de>

Thanks for finding the bug and testing the solution!
NeilBrown

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