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[Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer

Philippe Mathieu-Daudé posted 35 patches 8 years, 3 months ago
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[Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer
Posted by Philippe Mathieu-Daudé 8 years, 3 months ago 
Clang's scan-build-5.0 reports:

linux-user/syscall.c:5581:9: warning: Dereference of undefined pointer value
    if (*host_rt_dev_ptr != 0) {
        ^~~~~~~~~~~~~~~~

Reported-by: Clang Static Analyzer
Suggested-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 linux-user/syscall.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index fcd20fa276..e79b5baec4 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5524,7 +5524,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
     int target_size;
     void *argptr;
     abi_ulong *target_rt_dev_ptr;
-    unsigned long *host_rt_dev_ptr;
+    unsigned long *host_rt_dev_ptr = NULL;
     abi_long ret;
     int i;
 
@@ -5570,6 +5570,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
     unlock_user(argptr, arg, 0);
 
     ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));
+    assert(host_rt_dev_ptr);
     if (*host_rt_dev_ptr != 0) {
         unlock_user((void *)*host_rt_dev_ptr,
                     *target_rt_dev_ptr, 0);
-- 
2.13.3
Re: [Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer
Posted by Laurent Vivier 8 years, 3 months ago 
Le 24/07/2017 à 20:27, Philippe Mathieu-Daudé a écrit :
> Clang's scan-build-5.0 reports:
> 
> linux-user/syscall.c:5581:9: warning: Dereference of undefined pointer value
>     if (*host_rt_dev_ptr != 0) {
>         ^~~~~~~~~~~~~~~~
> 
> Reported-by: Clang Static Analyzer
> Suggested-by: Laurent Vivier <lvivier@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  linux-user/syscall.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index fcd20fa276..e79b5baec4 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5524,7 +5524,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>      int target_size;
>      void *argptr;
>      abi_ulong *target_rt_dev_ptr;
> -    unsigned long *host_rt_dev_ptr;
> +    unsigned long *host_rt_dev_ptr = NULL;
>      abi_long ret;
>      int i;
>  
> @@ -5570,6 +5570,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>      unlock_user(argptr, arg, 0);
>  
>      ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));
> +    assert(host_rt_dev_ptr);
>      if (*host_rt_dev_ptr != 0) {
>          unlock_user((void *)*host_rt_dev_ptr,
>                      *target_rt_dev_ptr, 0);
> 

I think if you add the assert you should not have to add the "= NULL".
Could you check?

Thanks,
Laurent
Re: [Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer
Posted by Philippe Mathieu-Daudé 8 years, 3 months ago 
On 07/24/2017 04:33 PM, Laurent Vivier wrote:
> Le 24/07/2017 à 20:27, Philippe Mathieu-Daudé a écrit :
>> Clang's scan-build-5.0 reports:
>>
>> linux-user/syscall.c:5581:9: warning: Dereference of undefined pointer value
>>      if (*host_rt_dev_ptr != 0) {
>>          ^~~~~~~~~~~~~~~~
>>
>> Reported-by: Clang Static Analyzer
>> Suggested-by: Laurent Vivier <lvivier@redhat.com>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>   linux-user/syscall.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> index fcd20fa276..e79b5baec4 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -5524,7 +5524,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>>       int target_size;
>>       void *argptr;
>>       abi_ulong *target_rt_dev_ptr;
>> -    unsigned long *host_rt_dev_ptr;
>> +    unsigned long *host_rt_dev_ptr = NULL;
>>       abi_long ret;
>>       int i;
>>   
>> @@ -5570,6 +5570,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>>       unlock_user(argptr, arg, 0);
>>   
>>       ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));
>> +    assert(host_rt_dev_ptr);
>>       if (*host_rt_dev_ptr != 0) {
>>           unlock_user((void *)*host_rt_dev_ptr,
>>                       *target_rt_dev_ptr, 0);
>>
> 
> I think if you add the assert you should not have to add the "= NULL".
> Could you check?

Indeed!

Thanks :)

Phil.
Re: [Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer
Posted by Peter Maydell 8 years, 3 months ago 
On 24 July 2017 at 19:27, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
> Clang's scan-build-5.0 reports:
>
> linux-user/syscall.c:5581:9: warning: Dereference of undefined pointer value
>     if (*host_rt_dev_ptr != 0) {
>         ^~~~~~~~~~~~~~~~
>
> Reported-by: Clang Static Analyzer
> Suggested-by: Laurent Vivier <lvivier@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>  linux-user/syscall.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index fcd20fa276..e79b5baec4 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5524,7 +5524,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>      int target_size;
>      void *argptr;
>      abi_ulong *target_rt_dev_ptr;
> -    unsigned long *host_rt_dev_ptr;
> +    unsigned long *host_rt_dev_ptr = NULL;
>      abi_long ret;
>      int i;
>
> @@ -5570,6 +5570,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>      unlock_user(argptr, arg, 0);
>
>      ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));
> +    assert(host_rt_dev_ptr);

There's not much point in this assert because it doesn't
tell us anything we're not about to find out immediately
by dereferencing the pointer...

>      if (*host_rt_dev_ptr != 0) {
>          unlock_user((void *)*host_rt_dev_ptr,
>                      *target_rt_dev_ptr, 0);
> --
> 2.13.3

thanks
-- PMM
Re: [Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer
Posted by Laurent Vivier 8 years, 3 months ago 
Le 24/07/2017 à 23:26, Peter Maydell a écrit :
> On 24 July 2017 at 19:27, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>> Clang's scan-build-5.0 reports:
>>
>> linux-user/syscall.c:5581:9: warning: Dereference of undefined pointer value
>>     if (*host_rt_dev_ptr != 0) {
>>         ^~~~~~~~~~~~~~~~
>>
>> Reported-by: Clang Static Analyzer
>> Suggested-by: Laurent Vivier <lvivier@redhat.com>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>  linux-user/syscall.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> index fcd20fa276..e79b5baec4 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -5524,7 +5524,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>>      int target_size;
>>      void *argptr;
>>      abi_ulong *target_rt_dev_ptr;
>> -    unsigned long *host_rt_dev_ptr;
>> +    unsigned long *host_rt_dev_ptr = NULL;
>>      abi_long ret;
>>      int i;
>>
>> @@ -5570,6 +5570,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, uint8_t *buf_temp,
>>      unlock_user(argptr, arg, 0);
>>
>>      ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));
>> +    assert(host_rt_dev_ptr);
> 
> There's not much point in this assert because it doesn't
> tell us anything we're not about to find out immediately
> by dereferencing the pointer...

It's just to shut off the warning.

What I said in the comment of the previous version of this patch:

I think we should "assert(host_rt_dev_ptr)" here. It's a bug if
host_rt_dev_ptr is not set.

The "for" loop scans the structure to find the rt_dev field, and we
should always enter in the first "if", so "host_rt_dev_ptr" is always set.

Thanks,
Laurent

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