Re: [Qemu-devel] [PATCH] linux-user/syscall: let recvfrom(struct sockaddr *) use abi_ulong

[Laurent Vivier <laurent@vivier.eu>]

Le 23/01/2018 à 16:23, Guido Günther a écrit :
> Hi,
> Thanks for having a look!
> 
> On Tue, Jan 23, 2018 at 11:52:22AM -0300, Philippe Mathieu-Daudé wrote:
>> Currently recvfrom() is restricted to handle 32-bit pointers,
>> remove this limit for 64-bit hosts.
>>
>> This fixes:
>>
>>   31572 socket(AF_NETLINK, SOCK_RAW, NETLINK_AUDIT) = 3
>>   ...
>>   31572 sendto(3, {{len=124, type=0x454 /* NLMSG_??? */, flags=NLM_F_REQUEST|NLM_F_ACK, seq=1, pid=0}, "op=test:message acct=\"?\" exe=\"/tmp/nl-bad-addr\" hostname=localhost addr=? terminal=/dev/pts/2 res=success\0\0\0"}, 124, 0, 0xfffffa3897d0, 0) = 124
>>   31572 ppoll([{fd=3, events=POLLIN}], 1, {tv_sec=0, tv_nsec=500000000}, NULL, 0) = 1 ([{fd=3, revents=POLLIN}], left {tv_sec=0, tv_nsec=499993180})
>>   31572 recvfrom(3, 0x112a50eb4, 8988, MSG_PEEK|MSG_DONTWAIT, 0xfffffa3897e0, 0x42) = -1 EFAULT (Bad address)
>>
>> Reported-by: Guido Günther <agx@sigxcpu.org>
>> Message-id: 20180123120541.GA14216@bogon.m.sigxcpu.org
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>  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 11c9116c4a..28805b1785 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -4032,7 +4032,7 @@ static abi_long do_recvfrom(int fd, abi_ulong msg, size_t len, int flags,
>>      if (!host_msg)
>>          return -TARGET_EFAULT;
>>      if (target_addr) {
>> -        if (get_user_u32(addrlen, target_addrlen)) {
>> +        if (get_user_ual(addrlen, target_addrlen)) {
>>              ret = -TARGET_EFAULT;
>>              goto fail;
>>          }
>> @@ -4053,7 +4053,7 @@ static abi_long do_recvfrom(int fd, abi_ulong msg, size_t len, int flags,
>>          }
>>          if (target_addr) {
>>              host_to_target_sockaddr(target_addr, addr, addrlen);
>> -            if (put_user_u32(addrlen, target_addrlen)) {
>> +            if (put_user_ual(addrlen, target_addrlen)) {
>>                  ret = -TARGET_EFAULT;
>>                  goto fail;
>>              }
> 
> Ahh...I saw these and was wondering how this would work on
> 64bit. Unfortunately the patch doesn't change things:
> 
>     4824  recvfrom(3, 0x1401f8eb4, 8988, MSG_PEEK|MSG_DONTWAIT, 0xffffe10a8620, 0x42) = -1 EFAULT (Bad address)
> 
> If you want me to report qemu -strace or s.th. please let me know.
> Cheers,
>  -- Guido
> 

Could you try:

strace -f chroot . /usr/bin/qemu-arm-static tmp/nl-bad-addr

to see if the fault comes from the kernel or from QEMU.

Thanks,
Laurent