[PATCH v5] netlink: decode libudev netlink header

Harsha Sharma harshasharmaiitr at gmail.com
Tue Feb 27 12:27:03 UTC 2018


On Mon, Feb 26, 2018 at 7:40 AM, Dmitry V. Levin <ldv at altlinux.org> wrote:
> On Wed, Jan 31, 2018 at 11:32:45PM +0530, Harsha Sharma wrote:
>> * defs.h (decode_netlink_kobject_uevent): New prototype.
>> * netlink.c (decode_netlink): Decode family kobject_uevent.
>> * netlink_kobject_uevent.h: New file.
>> * netlink_object_uevent.c: New file.
>> * Makefile.am (strace_SOURCES): Add them.
>>
>> Signed-off-by: Harsha Sharma <harshasharmaiitr at gmail.com>
>> ---
>> Changes in v5:
>> * print filter_* fields in hex
>> * print messages after header in correct way
>>
>> Changes in v4:
>> * Minor changes in decode_netlink_kobject_uevent
>>
>> Changes in v3:
>> * Change changelog
>> * minor changes in decode_netlink_kobject_uevent
>> * omit irrelevant comments in netlink_kobject_uevent.h
>>
>> Changes in v2:
>> * New file netlink_kobject_uevent.c
>> * change location of netlink_kobject_uevent.h
>> * add comments in netlink_kobject_uevent.h
>> * add new files in Makefile.am
>> * add func decode_netlink_kobject_uevent in defs.h
>> * Use macros from print_fields.h instead of tprintf
>> * minor changes in decode_netlink_kobject_uevent (including name)
>>
>>  Makefile.am              |  2 ++
>>  defs.h                   |  3 +++
>>  netlink.c                |  2 +-
>>  netlink_kobject_uevent.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  netlink_kobject_uevent.h | 17 ++++++++++++
>>  5 files changed, 90 insertions(+), 1 deletion(-)
>>  create mode 100644 netlink_kobject_uevent.c
>>  create mode 100644 netlink_kobject_uevent.h
>>
>> diff --git a/Makefile.am b/Makefile.am
>> index 065ab819..20f97b06 100644
>> --- a/Makefile.am
>> +++ b/Makefile.am
>> @@ -197,6 +197,8 @@ strace_SOURCES =  \
>>       netlink.c       \
>>       netlink.h       \
>>       netlink_crypto.c \
>> +     netlink_kobject_uevent.c \
>> +     netlink_kobject_uevent.h \
>>       netlink_sock_diag.h \
>>       netlink_inet_diag.c \
>>       netlink_netlink_diag.c \
>> diff --git a/defs.h b/defs.h
>> index bbe0ecc9..d80ebc47 100644
>> --- a/defs.h
>> +++ b/defs.h
>> @@ -685,6 +685,9 @@ DECL_NETLINK(route);
>>  DECL_NETLINK(selinux);
>>  DECL_NETLINK(sock_diag);
>>
>> +extern void
>> +decode_netlink_kobject_uevent(struct tcb *, kernel_ulong_t addr,
>> +                           kernel_ulong_t len);
>>  extern int tv_nz(const struct timeval *);
>>  extern int tv_cmp(const struct timeval *, const struct timeval *);
>>  extern double tv_float(const struct timeval *);
>> diff --git a/netlink.c b/netlink.c
>> index beb6ea4a..a714d29a 100644
>> --- a/netlink.c
>> +++ b/netlink.c
>> @@ -629,7 +629,7 @@ decode_netlink(struct tcb *const tcp,
>>       const int family = get_fd_nl_family(tcp, fd);
>>
>>       if (family == NETLINK_KOBJECT_UEVENT) {
>> -             printstrn(tcp, addr, len);
>> +             decode_netlink_kobject_uevent(tcp, addr, len);
>>               return;
>>       }
>>
>> diff --git a/netlink_kobject_uevent.c b/netlink_kobject_uevent.c
>> new file mode 100644
>> index 00000000..1ff7bd63
>> --- /dev/null
>> +++ b/netlink_kobject_uevent.c
>> @@ -0,0 +1,67 @@
>> +/*
>> + * Copyright (c) 2018 Harsha Sharma <harshasharmaiitr at gmail.com>
>> + * Copyright (c) 2017 The strace developers.
>> + * All rights reserved.
>> + *
>> + * Redistribution and use in source and binary forms, with or without
>> + * modification, are permitted provided that the following conditions
>> + * are met:
>> + * 1. Redistributions of source code must retain the above copyright
>> + *    notice, this list of conditions and the following disclaimer.
>> + * 2. Redistributions in binary form must reproduce the above copyright
>> + *    notice, this list of conditions and the following disclaimer in the
>> + *    documentation and/or other materials provided with the distribution.
>> + * 3. The name of the author may not be used to endorse or promote products
>> + *    derived from this software without specific prior written permission.
>> + *
>> + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
>> + * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
>> + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
>> + * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
>> + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
>> + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
>> + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
>> + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
>> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
>> + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
>> + */
>> +
>> +#include "defs.h"
>> +#include "print_fields.h"
>> +#include "netlink_kobject_uevent.h"
>> +
>> +#include <arpa/inet.h>
>> +
>> +void
>> +decode_netlink_kobject_uevent(struct tcb *tcp, kernel_ulong_t addr,
>> +                           kernel_ulong_t len)
>> +{
>> +     struct udev_monitor_netlink_header uh;
>> +     const char *prefix = "libudev";
>> +
>> +     if (len < sizeof(uh)) {
>> +             printstrn(tcp, addr, len);
>> +     } else if (!umove_or_printaddr(tcp, addr, &uh)) {
>> +             if (strcmp(uh.prefix, prefix) == 0) {
>> +                     PRINT_FIELD_CSTRING("{{", uh, prefix);
>> +                     tprintf(", magic=htonl(%#x)", ntohl(uh.magic));
>> +                     PRINT_FIELD_U(", ", uh, header_size);
>> +                     PRINT_FIELD_U(", ", uh, properties_off);
>> +                     PRINT_FIELD_U(", ", uh, properties_len);
>> +                     tprintf(", filter_subsystem_hash=htonl(%#x)", ntohl(uh.filter_subsystem_hash));
>> +                     tprintf(", filter_devtype_hash=htonl(%#x)", ntohl(uh.filter_devtype_hash));
>> +                     tprintf(", filter_tag_bloom_hi=htonl(%#x)", ntohl(uh.filter_tag_bloom_hi));
>> +                     tprintf(", filter_tag_bloom_lo=htonl(%#x)", ntohl(uh.filter_tag_bloom_lo));
>> +                     tprints("}");
>> +                     const size_t offset = CMSG_ALIGN(sizeof(uh));
>> +                     if (len > offset) {
>> +                             tprints(", ");
>> +                             printstrn(tcp, addr + offset , len - offset);
>> +                     }
>
> Are you sure the use of CMSG_ALIGN is correct here?
> It aligns on size_t boundary which is strange here given that
> sizeof(size_t) is architecture-dependent while netlink packets should not be,
> otherwise 32-bit clients won't be able to handle netlink packets sent by
> a 64-bit kernel.

Sorry my bad, Can I leave it as it was before i.e
offset = sizeof(uh)
Other than this, does this patch looks ok ?
Thanks for your time.

Regards,
Harsha Sharma

> --
> ldv
>
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