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From 4243bd97f3c703a75e795fdc6dd2273a7c74e85c Mon Sep 17 00:00:00 2001
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From: Phil Sutter <phil@nwl.cc>
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Date: Fri, 11 Feb 2022 17:47:22 +0100
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Subject: [PATCH] Improve error messages for unsupported extensions
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If a given extension was not supported by the kernel, iptables would
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print a rather confusing error message if extension parameters were
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given:
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| # rm /lib/modules/$(uname -r)/kernel/net/netfilter/xt_LOG.ko
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| # iptables -A FORWARD -j LOG --log-prefix foo
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| iptables v1.8.7 (legacy): unknown option "--log-prefix"
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Avoid this by pretending extension revision 0 is always supported. It is
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the same hack as used to successfully print extension help texts as
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unprivileged user, extended to all error codes to serve privileged ones
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as well.
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In addition, print a warning if kernel rejected revision 0 and it's not
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a permissions problem. This helps users find out which extension in a
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rule the kernel didn't like.
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Finally, the above commands result in these messages:
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| Warning: Extension LOG revision 0 not supported, missing kernel module?
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| iptables: No chain/target/match by that name.
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Or, for iptables-nft:
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| Warning: Extension LOG revision 0 not supported, missing kernel module?
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| iptables v1.8.7 (nf_tables): RULE_APPEND failed (No such file or directory): rule in chain FORWARD
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Signed-off-by: Phil Sutter <phil@nwl.cc>
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(cherry picked from commit 17534cb18ed0a5052dc45c117401251359dba6aa)
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---
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iptables/nft.c | 12 +++++++++---
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libxtables/xtables.c | 7 ++++++-
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2 files changed, 15 insertions(+), 4 deletions(-)
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diff --git a/iptables/nft.c b/iptables/nft.c
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index c5cc6f83bf573..9643abf2d0085 100644
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--- a/iptables/nft.c
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+++ b/iptables/nft.c
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@@ -3110,10 +3110,16 @@ int nft_compatible_revision(const char *name, uint8_t rev, int opt)
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err:
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mnl_socket_close(nl);
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- /* pretend revision 0 is valid if not permitted to check -
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- * this is required for printing extension help texts as user */
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- if (ret < 0 && errno == EPERM && rev == 0)
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+ /* pretend revision 0 is valid -
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+ * this is required for printing extension help texts as user, also
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+ * helps error messaging on unavailable kernel extension */
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+ if (ret < 0 && rev == 0) {
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+ if (errno != EPERM)
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+ fprintf(stderr,
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+ "Warning: Extension %s revision 0 not supported, missing kernel module?\n",
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+ name);
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return 1;
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+ }
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return ret < 0 ? 0 : 1;
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}
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diff --git a/libxtables/xtables.c b/libxtables/xtables.c
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index 57ad0330a454c..a5c8d7e2c17ef 100644
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--- a/libxtables/xtables.c
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+++ b/libxtables/xtables.c
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@@ -968,7 +968,12 @@ int xtables_compatible_revision(const char *name, uint8_t revision, int opt)
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/* Definitely don't support this? */
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if (errno == ENOENT || errno == EPROTONOSUPPORT) {
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close(sockfd);
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- return 0;
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+ /* Pretend revision 0 support for better error messaging */
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+ if (revision == 0)
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+ fprintf(stderr,
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+ "Warning: Extension %s revision 0 not supported, missing kernel module?\n",
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+ name);
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+ return (revision == 0);
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} else if (errno == ENOPROTOOPT) {
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close(sockfd);
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/* Assume only revision 0 support (old kernel) */
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--
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2.34.1
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