diff mbox series

[2/2] linux-user: Allow sendmsg() without IOV

Message ID 20221212173416.90590-2-deller@gmx.de
State New
Headers show
Series [1/2] linux-user: Implement SOL_ALG encryption support | expand

Commit Message

Helge Deller Dec. 12, 2022, 5:34 p.m. UTC 
Applications do call sendmsg() without any IOV, e.g.:
 sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
            msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
            msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
 sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over t"..., iov_len=183}],
            msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
            msg_controllen=24, msg_flags=0}, 0) = 183

The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
and calls lock_iovec() to lock the IOV into memory. For the first
sendmsg() above it returns NULL and thus wrongly skips the call the host
sendmsg() syscall, which will break the calling application.

Fix this issue by:
- allowing sendmsg() even with empty IOV
- skip recvmsg() if IOV is NULL
- skip both if the return code of do_sendrecvmsg_locked() != 0, which
  indicates some failure like EFAULT on the IOV

Tested with the debian "ell" package with hppa guest on x86_64 host.

Signed-off-by: Helge Deller <deller@gmx.de>
---
 linux-user/syscall.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--
2.38.1

Comments

Laurent Vivier Jan. 31, 2023, 12:28 p.m. UTC | #1 
Le 12/12/2022 à 18:34, Helge Deller a écrit :
> Applications do call sendmsg() without any IOV, e.g.:
>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
>              msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
>              msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over t"..., iov_len=183}],
>              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
>              msg_controllen=24, msg_flags=0}, 0) = 183
> 
> The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
> and calls lock_iovec() to lock the IOV into memory. For the first
> sendmsg() above it returns NULL and thus wrongly skips the call the host
> sendmsg() syscall, which will break the calling application.
> 
> Fix this issue by:
> - allowing sendmsg() even with empty IOV
> - skip recvmsg() if IOV is NULL
> - skip both if the return code of do_sendrecvmsg_locked() != 0, which
>    indicates some failure like EFAULT on the IOV
> 
> Tested with the debian "ell" package with hppa guest on x86_64 host.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> ---
>   linux-user/syscall.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index a365903a3a..9e2c0a18fc 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -3330,7 +3330,10 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
>                        target_vec, count, send);
>       if (vec == NULL) {
>           ret = -host_to_target_errno(errno);
> -        goto out2;
> +        /* allow sending packet without any iov, e.g. with MSG_MORE flag */

why don't you check only for count is 0?
Somehing like:

if (vec == NULL && (count || !send)) {
...

Thanks,
Laurent
Helge Deller Jan. 31, 2023, 1:34 p.m. UTC | #2 
On 1/31/23 13:28, Laurent Vivier wrote:
> Le 12/12/2022 à 18:34, Helge Deller a écrit :
>> Applications do call sendmsg() without any IOV, e.g.:
>>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
>>              msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
>>              msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
>>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over t"..., iov_len=183}],
>>              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
>>              msg_controllen=24, msg_flags=0}, 0) = 183
>>
>> The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
>> and calls lock_iovec() to lock the IOV into memory. For the first
>> sendmsg() above it returns NULL and thus wrongly skips the call the host
>> sendmsg() syscall, which will break the calling application.
>>
>> Fix this issue by:
>> - allowing sendmsg() even with empty IOV
>> - skip recvmsg() if IOV is NULL
>> - skip both if the return code of do_sendrecvmsg_locked() != 0, which
>>    indicates some failure like EFAULT on the IOV
>>
>> Tested with the debian "ell" package with hppa guest on x86_64 host.
>>
>> Signed-off-by: Helge Deller <deller@gmx.de>
>> ---
>>   linux-user/syscall.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> index a365903a3a..9e2c0a18fc 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -3330,7 +3330,10 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
>>                        target_vec, count, send);
>>       if (vec == NULL) {
>>           ret = -host_to_target_errno(errno);
>> -        goto out2;
>> +        /* allow sending packet without any iov, e.g. with MSG_MORE flag */
>
> why don't you check only for count is 0?
> Somehing like:
>
> if (vec == NULL && (count || !send)) {

You mean:
if (vec == NULL && (!count || !send)) {
	goto out2;

lock_iovec() sets errno=0 if count==0, but for invalid addresses it sets errno!=0,
so my current check (for which ret is the same as errno):
         if (!send || ret) {
             goto out2;
exits on memfaults too, while a check for just count==0 would succeed.

Helge
Helge Deller Jan. 31, 2023, 1:50 p.m. UTC | #3 
On 1/31/23 14:34, Helge Deller wrote:
> On 1/31/23 13:28, Laurent Vivier wrote:
>> Le 12/12/2022 à 18:34, Helge Deller a écrit :
>>> Applications do call sendmsg() without any IOV, e.g.:
>>>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
>>>              msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
>>>              msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
>>>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over t"..., iov_len=183}],
>>>              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
>>>              msg_controllen=24, msg_flags=0}, 0) = 183
>>>
>>> The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
>>> and calls lock_iovec() to lock the IOV into memory. For the first
>>> sendmsg() above it returns NULL and thus wrongly skips the call the host
>>> sendmsg() syscall, which will break the calling application.
>>>
>>> Fix this issue by:
>>> - allowing sendmsg() even with empty IOV
>>> - skip recvmsg() if IOV is NULL
>>> - skip both if the return code of do_sendrecvmsg_locked() != 0, which
>>>    indicates some failure like EFAULT on the IOV
>>>
>>> Tested with the debian "ell" package with hppa guest on x86_64 host.
>>>
>>> Signed-off-by: Helge Deller <deller@gmx.de>
>>> ---
>>>   linux-user/syscall.c | 9 +++++++--
>>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>>> index a365903a3a..9e2c0a18fc 100644
>>> --- a/linux-user/syscall.c
>>> +++ b/linux-user/syscall.c
>>> @@ -3330,7 +3330,10 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
>>>                        target_vec, count, send);
>>>       if (vec == NULL) {
>>>           ret = -host_to_target_errno(errno);
>>> -        goto out2;
>>> +        /* allow sending packet without any iov, e.g. with MSG_MORE flag */
>>
>> why don't you check only for count is 0?
>> Somehing like:
>>
>> if (vec == NULL && (count || !send)) {
>
> You mean:
> if (vec == NULL && (!count || !send)) {
>      goto out2;
>
> lock_iovec() sets errno=0 if count==0, but for invalid addresses it sets errno!=0,
> so my current check (for which ret is the same as errno):
>          if (!send || ret) {
>              goto out2;
> exits on memfaults too, while a check for just count==0 would succeed.

forget the above...
Maybe just checking for count==0 would be sufficient. I don't know yet if
there are any other corner cases where replacing the check of
           if (!send || ret) {
with
           if (!send || count==0) {
would behave different.
Checking against errno which is reported back from lock_iovec() seemed more
logical for me. This patch has been as-is in the buildd trees now since weeks
without any problems so far at least.

Helge
Laurent Vivier Jan. 31, 2023, 3:17 p.m. UTC | #4 
Le 31/01/2023 à 14:50, Helge Deller a écrit :
> On 1/31/23 14:34, Helge Deller wrote:
>> On 1/31/23 13:28, Laurent Vivier wrote:
>>> Le 12/12/2022 à 18:34, Helge Deller a écrit :
>>>> Applications do call sendmsg() without any IOV, e.g.:
>>>>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
>>>>              msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
>>>>              msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
>>>>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over 
>>>> t"..., iov_len=183}],
>>>>              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
>>>>              msg_controllen=24, msg_flags=0}, 0) = 183
>>>>
>>>> The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
>>>> and calls lock_iovec() to lock the IOV into memory. For the first
>>>> sendmsg() above it returns NULL and thus wrongly skips the call the host
>>>> sendmsg() syscall, which will break the calling application.
>>>>
>>>> Fix this issue by:
>>>> - allowing sendmsg() even with empty IOV
>>>> - skip recvmsg() if IOV is NULL
>>>> - skip both if the return code of do_sendrecvmsg_locked() != 0, which
>>>>    indicates some failure like EFAULT on the IOV
>>>>
>>>> Tested with the debian "ell" package with hppa guest on x86_64 host.
>>>>
>>>> Signed-off-by: Helge Deller <deller@gmx.de>
>>>> ---
>>>>   linux-user/syscall.c | 9 +++++++--
>>>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>>>> index a365903a3a..9e2c0a18fc 100644
>>>> --- a/linux-user/syscall.c
>>>> +++ b/linux-user/syscall.c
>>>> @@ -3330,7 +3330,10 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
>>>>                        target_vec, count, send);
>>>>       if (vec == NULL) {
>>>>           ret = -host_to_target_errno(errno);
>>>> -        goto out2;
>>>> +        /* allow sending packet without any iov, e.g. with MSG_MORE flag */
>>>
>>> why don't you check only for count is 0?
>>> Somehing like:
>>>
>>> if (vec == NULL && (count || !send)) {
>>
>> You mean:
>> if (vec == NULL && (!count || !send)) {
>>      goto out2;
>>
>> lock_iovec() sets errno=0 if count==0, but for invalid addresses it sets errno!=0,
>> so my current check (for which ret is the same as errno):
>>          if (!send || ret) {
>>              goto out2;
>> exits on memfaults too, while a check for just count==0 would succeed.
> 
> forget the above...
> Maybe just checking for count==0 would be sufficient. I don't know yet if
> there are any other corner cases where replacing the check of
>            if (!send || ret) {
> with
>            if (!send || count==0) {
> would behave different.
> Checking against errno which is reported back from lock_iovec() seemed more
> logical for me. This patch has been as-is in the buildd trees now since weeks
> without any problems so far at least.
> 

It seems kernel also checks for the invalid address even with count=0, so I'm going to apply this 
patch as-is.

Thanks,
Laurent
Laurent Vivier Jan. 31, 2023, 3:17 p.m. UTC | #5 
Le 12/12/2022 à 18:34, Helge Deller a écrit :
> Applications do call sendmsg() without any IOV, e.g.:
>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
>              msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
>              msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over t"..., iov_len=183}],
>              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
>              msg_controllen=24, msg_flags=0}, 0) = 183
> 
> The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
> and calls lock_iovec() to lock the IOV into memory. For the first
> sendmsg() above it returns NULL and thus wrongly skips the call the host
> sendmsg() syscall, which will break the calling application.
> 
> Fix this issue by:
> - allowing sendmsg() even with empty IOV
> - skip recvmsg() if IOV is NULL
> - skip both if the return code of do_sendrecvmsg_locked() != 0, which
>    indicates some failure like EFAULT on the IOV
> 
> Tested with the debian "ell" package with hppa guest on x86_64 host.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> ---
>   linux-user/syscall.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Laurent Vivier Jan. 31, 2023, 3:19 p.m. UTC | #6 
Le 12/12/2022 à 18:34, Helge Deller a écrit :
> Applications do call sendmsg() without any IOV, e.g.:
>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=NULL, msg_iovlen=0,
>              msg_control=[{cmsg_len=36, cmsg_level=SOL_ALG, cmsg_type=0x2}],
>              msg_controllen=40, msg_flags=0}, MSG_MORE) = 0
>   sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="The quick brown fox jumps over t"..., iov_len=183}],
>              msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_ALG, cmsg_type=0x3}],
>              msg_controllen=24, msg_flags=0}, 0) = 183
> 
> The function do_sendrecvmsg_locked() is used for sndmsg() and recvmsg()
> and calls lock_iovec() to lock the IOV into memory. For the first
> sendmsg() above it returns NULL and thus wrongly skips the call the host
> sendmsg() syscall, which will break the calling application.
> 
> Fix this issue by:
> - allowing sendmsg() even with empty IOV
> - skip recvmsg() if IOV is NULL
> - skip both if the return code of do_sendrecvmsg_locked() != 0, which
>    indicates some failure like EFAULT on the IOV
> 
> Tested with the debian "ell" package with hppa guest on x86_64 host.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> ---
>   linux-user/syscall.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index a365903a3a..9e2c0a18fc 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -3330,7 +3330,10 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
>                        target_vec, count, send);
>       if (vec == NULL) {
>           ret = -host_to_target_errno(errno);
> -        goto out2;
> +        /* allow sending packet without any iov, e.g. with MSG_MORE flag */
> +        if (!send || ret) {
> +            goto out2;
> +        }
>       }
>       msg.msg_iovlen = count;
>       msg.msg_iov = vec;
> @@ -3382,7 +3385,9 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
>       }
> 
>   out:
> -    unlock_iovec(vec, target_vec, count, !send);
> +    if (vec) {
> +        unlock_iovec(vec, target_vec, count, !send);
> +    }
>   out2:
>       return ret;
>   }
> --
> 2.38.1
> 
> 

Applied to my linux-user-for-8.0 branch.

Thanks,
Laurent
diff mbox series

Patch

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index a365903a3a..9e2c0a18fc 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -3330,7 +3330,10 @@  static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
                      target_vec, count, send);
     if (vec == NULL) {
         ret = -host_to_target_errno(errno);
-        goto out2;
+        /* allow sending packet without any iov, e.g. with MSG_MORE flag */
+        if (!send || ret) {
+            goto out2;
+        }
     }
     msg.msg_iovlen = count;
     msg.msg_iov = vec;
@@ -3382,7 +3385,9 @@  static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp,
     }

 out:
-    unlock_iovec(vec, target_vec, count, !send);
+    if (vec) {
+        unlock_iovec(vec, target_vec, count, !send);
+    }
 out2:
     return ret;
 }