Re: [lwip-devel] Invalid memory references when using lwip_gethostbyname()

[Simon Goldschmidt]

Fixed that, too. Thanks for reporting. Although next time, please create a bug 
tracker entry at savannah for bugs like this one, as a mail on this list might 
go unnoticed (if I wasn't sitting in front of the PC when it arrives).

Simon


Bjoern Doebel wrote:
> Hello again,
> 
> another issue I came across might be in lwip_gethostbyname() in
> api/netdb.c.
> 
> gethostbyname() returns a hostent containing a NULL-terminated list of
> IP addresses. When building lwip with LWIP_DNS_API_HOSTENT_STORAGE ==
> 0, the hostent returned from lwip_gethostbyname() is a statically
> allocated entry in this function and entry's h_addr_list pointer is
> set to point to another single statically allocated object. This lacks
> the explicit final NULL entry in h_addr_list and potentially (and in
> my case really) leads to invalid memory accesses due to calling code
> running through this list in search for a terminating NULL.
> 
> My current fix is:
> 
> Index: src/api/netdb.c
> ===================================================================
> RCS file: /sources/lwip/lwip/src/api/netdb.c,v
> retrieving revision 1.17
> diff -u -r1.17 netdb.c
> --- src/api/netdb.c   16 Mar 2010 15:14:14 -0000      1.17
> +++ src/api/netdb.c   17 May 2010 06:45:07 -0000
> @@ -91,7 +91,7 @@
>    HOSTENT_STORAGE struct hostent s_hostent;
>    HOSTENT_STORAGE char *s_aliases;
>    HOSTENT_STORAGE ip_addr_t s_hostent_addr;
> -  HOSTENT_STORAGE ip_addr_t *s_phostent_addr;
> +  HOSTENT_STORAGE ip_addr_t *s_phostent_addr[2] = { 0 };
> 
>    /* query host IP address */
>    err = netconn_gethostbyname(name, &addr);
> @@ -103,7 +103,7 @@
> 
>    /* fill hostent */
>    s_hostent_addr = addr;
> -  s_phostent_addr = &s_hostent_addr;
> +  s_phostent_addr[0] = &s_hostent_addr;
>    s_hostent.h_name = (char*)name;
>    s_hostent.h_aliases = &s_aliases;
>    s_hostent.h_addrtype = AF_INET;
> 
> 
> Regards,
> Bjoern
> 
> _______________________________________________
> lwip-devel mailing list
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