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[Qemu-devel] [PATCH] Avoid crash in epoll_ctl with EPOLL_CTL_DEL

Giuseppe Musacchio posted 1 patch 6 years, 8 months ago
Failed in applying to current master (apply log)
linux-user/syscall.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
[Qemu-devel] [PATCH] Avoid crash in epoll_ctl with EPOLL_CTL_DEL
Posted by Giuseppe Musacchio 6 years, 8 months ago 
The `event` parameter is ignored by the kernel if `op` is EPOLL_CTL_DEL,
do the same and avoid returning EFAULT if garbage is passed instead of a
valid pointer.

Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com>
---
  linux-user/syscall.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5e29e675e9..32d463d58d 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -11329,7 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int 
num, abi_long arg1,
      {
          struct epoll_event ep;
          struct epoll_event *epp = 0;
-        if (arg4) {
+        if (arg2 != EPOLL_CTL_DEL && arg4) {
              struct target_epoll_event *target_ep;
              if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
                  return -TARGET_EFAULT;
-- 
2.20.1
Re: [Qemu-devel] [PATCH] Avoid crash in epoll_ctl with EPOLL_CTL_DEL
Posted by Laurent Vivier 6 years, 8 months ago 
Le 30/05/2019 à 17:25, Giuseppe Musacchio a écrit :
> The `event` parameter is ignored by the kernel if `op` is EPOLL_CTL_DEL,
> do the same and avoid returning EFAULT if garbage is passed instead of a
> valid pointer.
> 
> Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com>
> ---
>  linux-user/syscall.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 5e29e675e9..32d463d58d 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -11329,7 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int
> num, abi_long arg1,
>      {
>          struct epoll_event ep;
>          struct epoll_event *epp = 0;
> -        if (arg4) {
> +        if (arg2 != EPOLL_CTL_DEL && arg4) {
>              struct target_epoll_event *target_ep;
>              if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
>                  return -TARGET_EFAULT;

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Re: [Qemu-devel] [PATCH] Avoid crash in epoll_ctl with EPOLL_CTL_DEL
Posted by Laurent Vivier 6 years, 8 months ago 
Le 30/05/2019 à 18:00, Laurent Vivier a écrit :
> Le 30/05/2019 à 17:25, Giuseppe Musacchio a écrit :
>> The `event` parameter is ignored by the kernel if `op` is EPOLL_CTL_DEL,
>> do the same and avoid returning EFAULT if garbage is passed instead of a
>> valid pointer.
>>
>> Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com>
>> ---
>>  linux-user/syscall.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> index 5e29e675e9..32d463d58d 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -11329,7 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int
>> num, abi_long arg1,
>>      {
>>          struct epoll_event ep;
>>          struct epoll_event *epp = 0;
>> -        if (arg4) {
>> +        if (arg2 != EPOLL_CTL_DEL && arg4) {
>>              struct target_epoll_event *target_ep;
>>              if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
>>                  return -TARGET_EFAULT;
> 
> Reviewed-by: Laurent Vivier <laurent@vivier.eu>
> 

in fact, the BUGS section of epoll_ctl(2) says:

"In kernel versions before 2.6.9, the EPOLL_CTL_DEL operation required a
 non-null pointer in event, even though this argument is ignored.  Since
 Linux 2.6.9, event can be specified as NULL when  using  EPOLL_CTL_DEL.
 Applications  that  need  to be portable to kernels before 2.6.9 should
 specify a non-null pointer in event."

So something like this would be more portable:

@@ -11329,6 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int
num, abi_long arg1,
         struct epoll_event ep;
         struct epoll_event *epp = 0;
         if (arg4) {
+            if (arg2 != EPOLL_CTL_DEL) {
                 struct target_epoll_event *target_ep;
                 if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
                     return -TARGET_EFAULT;
@@ -11340,6 +11341,11 @@ static abi_long do_syscall1(void *cpu_env, int
num, abi_long arg1,
                  */
                 ep.data.u64 = tswap64(target_ep->data.u64);
                 unlock_user_struct(target_ep, arg4, 0);
+            }
+            /*
+             * before kernel 2.6.9, EPOLL_CTL_DEL operation required a
+             * non-null pointer, even though this argument is ignored.
+             * */
             epp = &ep;
         }

Thanks,
Laurent
Re: [Qemu-devel] [PATCH] Avoid crash in epoll_ctl with EPOLL_CTL_DEL
Posted by Giuseppe Musacchio 6 years, 8 months ago 
Yes, that's much better if compatibility with such an old kernel version 
is wanted.

I suppose there's no need for me to re-send the patch.

On 30/05/19 18:12, Laurent Vivier wrote:
> Le 30/05/2019 à 18:00, Laurent Vivier a écrit :
>> Le 30/05/2019 à 17:25, Giuseppe Musacchio a écrit :
>>> The `event` parameter is ignored by the kernel if `op` is EPOLL_CTL_DEL,
>>> do the same and avoid returning EFAULT if garbage is passed instead of a
>>> valid pointer.
>>>
>>> Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com>
>>> ---
>>>   linux-user/syscall.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>>> index 5e29e675e9..32d463d58d 100644
>>> --- a/linux-user/syscall.c
>>> +++ b/linux-user/syscall.c
>>> @@ -11329,7 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int
>>> num, abi_long arg1,
>>>       {
>>>           struct epoll_event ep;
>>>           struct epoll_event *epp = 0;
>>> -        if (arg4) {
>>> +        if (arg2 != EPOLL_CTL_DEL && arg4) {
>>>               struct target_epoll_event *target_ep;
>>>               if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
>>>                   return -TARGET_EFAULT;
>>
>> Reviewed-by: Laurent Vivier <laurent@vivier.eu>
>>
> 
> in fact, the BUGS section of epoll_ctl(2) says:
> 
> "In kernel versions before 2.6.9, the EPOLL_CTL_DEL operation required a
>   non-null pointer in event, even though this argument is ignored.  Since
>   Linux 2.6.9, event can be specified as NULL when  using  EPOLL_CTL_DEL.
>   Applications  that  need  to be portable to kernels before 2.6.9 should
>   specify a non-null pointer in event."
> 
> So something like this would be more portable:
> 
> @@ -11329,6 +11329,7 @@ static abi_long do_syscall1(void *cpu_env, int
> num, abi_long arg1,
>           struct epoll_event ep;
>           struct epoll_event *epp = 0;
>           if (arg4) {
> +            if (arg2 != EPOLL_CTL_DEL) {
>                   struct target_epoll_event *target_ep;
>                   if (!lock_user_struct(VERIFY_READ, target_ep, arg4, 1)) {
>                       return -TARGET_EFAULT;
> @@ -11340,6 +11341,11 @@ static abi_long do_syscall1(void *cpu_env, int
> num, abi_long arg1,
>                    */
>                   ep.data.u64 = tswap64(target_ep->data.u64);
>                   unlock_user_struct(target_ep, arg4, 0);
> +            }
> +            /*
> +             * before kernel 2.6.9, EPOLL_CTL_DEL operation required a
> +             * non-null pointer, even though this argument is ignored.
> +             * */
>               epp = &ep;
>           }
> 
> Thanks,
> Laurent
>

Patchew 2.1-devel-b67e4c2

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