[PATCH ethtool 1/2] netlink: fix use after free in netlink_run_handler()

[Michal Kubecek]

Valgrind detected use after free in netlink_run_handler(): some members of
struct nl_context are accessed after the netlink context is freed by
netlink_done(). Use local variables to store the two flags and check them
instead.

Fixes: 6c19c0d559c8 ("netlink: use genetlink ops information to decide about 
fallback")
Signed-off-by: Michal Kubecek <mkube...@suse.cz>
---
 netlink/netlink.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/netlink/netlink.c b/netlink/netlink.c
index f655f6ea25b7..aaaabdd3048e 100644
--- a/netlink/netlink.c
+++ b/netlink/netlink.c
@@ -457,6 +457,7 @@ void netlink_run_handler(struct cmd_context *ctx, nl_func_t 
nlfunc,
                         bool no_fallback)
 {
        bool wildcard = ctx->devname && !strcmp(ctx->devname, WILDCARD_DEVNAME);
+       bool wildcard_unsupported, ioctl_fallback;
        struct nl_context *nlctx;
        const char *reason;
        int ret;
@@ -478,14 +479,17 @@ void netlink_run_handler(struct cmd_context *ctx, 
nl_func_t nlfunc,
        nlctx = ctx->nlctx;
 
        ret = nlfunc(ctx);
+       wildcard_unsupported = nlctx->wildcard_unsupported;
+       ioctl_fallback = nlctx->ioctl_fallback;
        netlink_done(ctx);
-       if (no_fallback || ret != -EOPNOTSUPP || !nlctx->ioctl_fallback) {
-               if (nlctx->wildcard_unsupported)
+
+       if (no_fallback || ret != -EOPNOTSUPP || !ioctl_fallback) {
+               if (wildcard_unsupported)
                        fprintf(stderr, "%s\n",
                                "subcommand does not support wildcard dump");
                exit(ret >= 0 ? ret : 1);
        }
-       if (nlctx->wildcard_unsupported)
+       if (wildcard_unsupported)
                reason = "subcommand does not support wildcard dump";
        else
                reason = "kernel netlink support for subcommand missing";
-- 
2.29.2