[PATCH] linux-user: Fix 'semop()' and 'semtimedop()' implementation

[PATCH] linux-user: Fix 'semop()' and 'semtimedop()' implementation

[Filip Bozuta]

The implementations of syscalls 'semop()' and 'semtimedop()' in
file 'syscall.c' use function 'target_to_host_sembuf()' to convert
values of 'struct sembuf' from host to target. However, before this
conversion it should be check whether the number of semaphore operations
'nsops' is not bigger than maximum allowed semaphor operations per
syscall: 'SEMOPM'. In these cases, errno 'E2BIG' ("Arg list too long")
should be set. But the implementation will set errno 'EFAULT' ("Bad address")
in this case since the conversion from target to host fails.

This was confirmed with the LTP test for 'semop()' ('ipc/semop/semop02') in
test case where 'nsops' is greater than SEMOPM with unaproppriate errno EFAULT:

semop02.c:130: FAIL: semop failed unexpectedly; expected: E2BIG: EFAULT (14)

This patch changes this by adding a check whether 'nsops' is bigger than
'SEMOPM' before the conversion function 'target_to_host_sembuf()' is called.
After the changes from this patch, the test works fine along with the other
LTP testcases for 'semop()'):

semop02.c:126: PASS: semop failed as expected: E2BIG (7)

Implementation notes:

    A target value ('TARGET_SEMOPM') was added for 'SEMOPM' as to be sure
    in case the value is not available for some targets.

Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
---
 linux-user/syscall.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 1211e759c2..4743a5bef2 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -3899,6 +3899,8 @@ static inline abi_long target_to_host_sembuf(struct sembuf *host_sembuf,
   (__nsops), 0, (__sops), (__timeout)
 #endif
 
+#define TARGET_SEMOPM 500
+
 static inline abi_long do_semtimedop(int semid,
                                      abi_long ptr,
                                      unsigned nsops,
@@ -3915,8 +3917,13 @@ static inline abi_long do_semtimedop(int semid,
         }
     }
 
-    if (target_to_host_sembuf(sops, ptr, nsops))
+    if (nsops > TARGET_SEMOPM) {
+        return -TARGET_E2BIG;
+    }
+
+    if (target_to_host_sembuf(sops, ptr, nsops)) {
         return -TARGET_EFAULT;
+    }
 
     ret = -TARGET_ENOSYS;
 #ifdef __NR_semtimedop
-- 
2.25.1

Re: [PATCH] linux-user: Fix 'semop()' and 'semtimedop()' implementation

[Laurent Vivier]

Le 12/08/2020 à 16:07, Filip Bozuta a écrit :
> The implementations of syscalls 'semop()' and 'semtimedop()' in
> file 'syscall.c' use function 'target_to_host_sembuf()' to convert
> values of 'struct sembuf' from host to target. However, before this
> conversion it should be check whether the number of semaphore operations
> 'nsops' is not bigger than maximum allowed semaphor operations per
> syscall: 'SEMOPM'. In these cases, errno 'E2BIG' ("Arg list too long")
> should be set. But the implementation will set errno 'EFAULT' ("Bad address")
> in this case since the conversion from target to host fails.
> 
> This was confirmed with the LTP test for 'semop()' ('ipc/semop/semop02') in
> test case where 'nsops' is greater than SEMOPM with unaproppriate errno EFAULT:
> 
> semop02.c:130: FAIL: semop failed unexpectedly; expected: E2BIG: EFAULT (14)
> 
> This patch changes this by adding a check whether 'nsops' is bigger than
> 'SEMOPM' before the conversion function 'target_to_host_sembuf()' is called.
> After the changes from this patch, the test works fine along with the other
> LTP testcases for 'semop()'):
> 
> semop02.c:126: PASS: semop failed as expected: E2BIG (7)
> 
> Implementation notes:
> 
>     A target value ('TARGET_SEMOPM') was added for 'SEMOPM' as to be sure
>     in case the value is not available for some targets.
> 
> Signed-off-by: Filip Bozuta <Filip.Bozuta@syrmia.com>
> ---
>  linux-user/syscall.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 1211e759c2..4743a5bef2 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -3899,6 +3899,8 @@ static inline abi_long target_to_host_sembuf(struct sembuf *host_sembuf,
>    (__nsops), 0, (__sops), (__timeout)
>  #endif
>  
> +#define TARGET_SEMOPM 500
> +

I think you could use directly SEMOPM as it is the same everywhere.

>  static inline abi_long do_semtimedop(int semid,
>                                       abi_long ptr,
>                                       unsigned nsops,
> @@ -3915,8 +3917,13 @@ static inline abi_long do_semtimedop(int semid,
>          }
>      }
>  
> -    if (target_to_host_sembuf(sops, ptr, nsops))
> +    if (nsops > TARGET_SEMOPM) {

You might move the check before allocation of the memory for sops.

> +        return -TARGET_E2BIG;
> +    }
> +
> +    if (target_to_host_sembuf(sops, ptr, nsops)) {
>          return -TARGET_EFAULT;
> +    }
>  
>      ret = -TARGET_ENOSYS;
>  #ifdef __NR_semtimedop
> 

Thanks,
Laurent