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libgenl: make genl_add_mcast_grp set errno on error 

genl_add_mcast_grp doesn't set errno in all cases.

On kernels that support mptcp but lack event support (all kernels <= 5.11)
MPTCP_PM_EV_GRP_NAME won't be found and ip will exit with

    "can't subscribe to mptcp events: Success"

Set errno to a meaningful value (ENOENT) when the group name isn't found
and also cover other spots where it returns nonzero with errno unset.

Fixes: ff619e4fd3 ("mptcp: add support for event monitoring")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
This commit is contained in:
Florian Westphal 2021-05-17 07:10:10 +02:00 committed by Stephen Hemminger
parent 2363bc99f9
commit d3740fdc26
1 changed files with 9 additions and 2 deletions
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11
lib/libgenl.c
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@ -3,6 +3,7 @@
* libgenl.c GENL library * libgenl.c GENL library
*/ */
#include <errno.h>
#include <stdio.h> #include <stdio.h>
#include <stdlib.h> #include <stdlib.h>
#include <unistd.h> #include <unistd.h>
@ -84,6 +85,7 @@ static int genl_parse_grps(struct rtattr *attr, const char *name, unsigned int *
} }
} }
errno = ENOENT;
return -1; return -1;
} }
@ -108,17 +110,22 @@ int genl_add_mcast_grp(struct rtnl_handle *grth, __u16 fnum, const char *group)
ghdr = NLMSG_DATA(answer); ghdr = NLMSG_DATA(answer);
len = answer->nlmsg_len; len = answer->nlmsg_len;
if (answer->nlmsg_type != GENL_ID_CTRL) if (answer->nlmsg_type != GENL_ID_CTRL) {
errno = EINVAL;
goto err_free; goto err_free;
}
len -= NLMSG_LENGTH(GENL_HDRLEN); len -= NLMSG_LENGTH(GENL_HDRLEN);
if (len < 0) if (len < 0) {
errno = EINVAL;
goto err_free; goto err_free;
}
attrs = (struct rtattr *) ((char *) ghdr + GENL_HDRLEN); attrs = (struct rtattr *) ((char *) ghdr + GENL_HDRLEN);
parse_rtattr(tb, CTRL_ATTR_MAX, attrs, len); parse_rtattr(tb, CTRL_ATTR_MAX, attrs, len);
if (tb[CTRL_ATTR_MCAST_GROUPS] == NULL) { if (tb[CTRL_ATTR_MCAST_GROUPS] == NULL) {
errno = ENOENT;
fprintf(stderr, "Missing mcast groups TLV\n"); fprintf(stderr, "Missing mcast groups TLV\n");
goto err_free; goto err_free;
} }