[v1] linux-user: don't short-circuit read with zero length

[Qemu-devel] [PATCH] linux-user: don't short-circuit read with zero length

Posted by Andreas Schwab 6 years, 8 months ago

A zero-length read still needs to do the usual checks, thus it may return
errors like EBADF.  This makes the read syscall emulation consistent with
the pread64 syscall emulation.

Signed-off-by: Andreas Schwab <schwab@suse.de>
---
 linux-user/syscall.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index ff912e89e1..7fac8e318f 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -7047,8 +7047,8 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
         _exit(arg1);
         return 0; /* avoid warning */
     case TARGET_NR_read:
-        if (arg3 == 0) {
-            return 0;
+        if (arg2 == 0 && arg3 == 0) {
+            return get_errno(safe_read(arg1, 0, 0));
         } else {
             if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
                 return -TARGET_EFAULT;
-- 
2.21.0

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Re: [Qemu-devel] [PATCH] linux-user: don't short-circuit read with zero length

Posted by Laurent Vivier 6 years, 8 months ago

Le 05/03/2019 à 17:45, Andreas Schwab a écrit :
> A zero-length read still needs to do the usual checks, thus it may return
> errors like EBADF.  This makes the read syscall emulation consistent with
> the pread64 syscall emulation.
> 
> Signed-off-by: Andreas Schwab <schwab@suse.de>
> ---
>  linux-user/syscall.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index ff912e89e1..7fac8e318f 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7047,8 +7047,8 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>          _exit(arg1);
>          return 0; /* avoid warning */
>      case TARGET_NR_read:
> -        if (arg3 == 0) {
> -            return 0;
> +        if (arg2 == 0 && arg3 == 0) {
> +            return get_errno(safe_read(arg1, 0, 0));
>          } else {
>              if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
>                  return -TARGET_EFAULT;
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>

Re: [Qemu-devel] [PATCH] linux-user: don't short-circuit read with zero length

Posted by Laurent Vivier 6 years, 8 months ago

On 05/03/2019 17:45, Andreas Schwab wrote:
> A zero-length read still needs to do the usual checks, thus it may return
> errors like EBADF.  This makes the read syscall emulation consistent with
> the pread64 syscall emulation.
> 
> Signed-off-by: Andreas Schwab <schwab@suse.de>
> ---
>  linux-user/syscall.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index ff912e89e1..7fac8e318f 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7047,8 +7047,8 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
>          _exit(arg1);
>          return 0; /* avoid warning */
>      case TARGET_NR_read:
> -        if (arg3 == 0) {
> -            return 0;
> +        if (arg2 == 0 && arg3 == 0) {
> +            return get_errno(safe_read(arg1, 0, 0));
>          } else {
>              if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
>                  return -TARGET_EFAULT;
> 

Applied to my linux-user branch.

Thanks,
Laurent