[Bug 1413] New: Inconsistent EBUSY errors when adding a duplicate element to a map

[bugzilla-daemon at netfilter.org]

https://bugzilla.netfilter.org/show_bug.cgi?id=1413

            Bug ID: 1413
           Summary: Inconsistent EBUSY errors when adding a duplicate
                    element to a map
           Product: nftables
           Version: unspecified
          Hardware: x86_64
                OS: Debian GNU/Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: kernel
          Assignee: pablo at netfilter.org
          Reporter: anton.aksola at upcloud.com

OS: Debian GNU/Linux 10 (Buster)
Kernel: 4.19.0-8-amd64

This works every time:
# nft -f - << EOF
flush ruleset
add table ip filter
add chain ip filter forward { type filter hook forward priority 0; policy
accept; }
add map ip filter foo { type ifname : verdict; }
add rule ip filter forward iifname vmap @foo
add element ip filter foo { "dummy0" : accept }
add element ip filter foo { "dummy0" : accept }
EOF

While these do not:
# nft -f - << EOF
flush ruleset
add table ip filter
add chain ip filter forward { type filter hook forward priority 0; policy
accept; }
add map ip filter foo { type ifname : verdict; }
add rule ip filter forward iifname vmap @foo
add element ip filter foo { "dummy0" : accept }
add element ip filter foo { "dummy0" : drop }
EOF
/dev/stdin:7:1-42: Error: Could not process rule: Device or resource busy
add element ip filter foo { "dummy0" : drop }
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

# nft -f - << EOF
flush ruleset
add table ip filter
add chain ip filter forward { type filter hook forward priority 0; policy
accept; }
add map ip filter foo { type ifname : verdict; }
add rule ip filter forward iifname vmap @foo
add element ip filter foo { "dummy0" : accept }
add set ip filter prefixset { type ipv4_addr; flags interval; }
add element ip filter foo { "dummy0" : accept }
EOF
/dev/stdin:8:1-44: Error: Could not process rule: Device or resource busy
add element ip filter foo { "dummy0" : accept }
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I couldn't find any references how maps should behave when adding a duplicate
element. In any case a consistent behaviour would be desirable.

Looking at the strace output this error seems to come from the kernel so filing
this under it.

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