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common: explain why mlock() failed instead of a bare abort #9438

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common: explain why mlock() failed instead of a bare abort #9438

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17 changes: 16 additions & 1 deletion common/utils.c
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
#include "config.h"
#include <assert.h>
#include <bitcoin/chainparams.h>
#include <ccan/err/err.h>
#include <ccan/list/list.h>
#include <ccan/mem/mem.h>
#include <ccan/str/hex/hex.h>
Expand All @@ -11,6 +12,7 @@
#include <errno.h>
#include <locale.h>
#include <sodium.h>
#include <string.h>

const tal_t *wally_tal_ctx = NULL;
secp256k1_context *secp256k1_ctx;
Expand Down Expand Up @@ -100,8 +102,21 @@ static void destroy_munlock(const tal_t *ptr)

void mlock_tal_memory(const tal_t *ptr)
{
if (sodium_mlock((void *)ptr, tal_bytelen(ptr)) != 0)

@Andezion Andezion Aug 20, 2026

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daemon_setup() already calls err_set_progname(argv0) (via common_setup) before mlock_tal_memory() can run. Did you consider using ccan warn()/warnx() instead of a hand-rolled fprintf + strerror, so the message gets the daemon-name prefix for free and matches the warnx() call in crashdump() that immediately follows it on the same failure path?

@mattraydub mattraydub Aug 20, 2026

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Good catch — no, I'd missed that common_setup() calls err_set_progname(argv0)
(common/setup.c:43) before any of these call sites. Switched to warnx().

One wrinkle in case it comes up: warn() appends : strerror(errno) to the end of
the whole string, which would leave the errno dangling after the Docker/Podman line,
so I've kept warnx() with strerror(errno) inline on the first line where it
belongs. Dropping fprintf also lets the added #include <stdio.h> go again;
<string.h> stays for strerror.

Verified end-to-end on FreeBSD 15.1 / clang 19, in a jail with allow.mlock=0
(which is the case that prompted the patch):

lightning_hsmd: FATAL: could not lock 64 bytes of sensitive memory into RAM: Operation not permitted
Memory locking is required to keep secrets out of swap.
If you are running in a container or jail, the privilege must be granted:
  FreeBSD jail: set allow.mlock=1 for the jail
  Linux: raise RLIMIT_MEMLOCK (ulimit -l), or grant the CAP_IPC_LOCK capability
  Docker/Podman: --ulimit memlock=-1:-1 or --cap-add=IPC_LOCK
lightning_hsmd: FATAL SIGNAL 6 (version 1f86c30-modded)

Which I think makes your point better than I could: with warnx() the diagnostic and
the crashdump() line beneath it now carry the same lightning_hsmd: prefix and read
as one block. Full tree builds clean, no new warnings on common/utils.c (also checked
with -Werror -Wformat=2 added).

if (sodium_mlock((void *)ptr, tal_bytelen(ptr)) != 0) {
warnx("FATAL: could not lock %zu bytes of sensitive memory"
" into RAM: %s\n"
"Memory locking is required to keep secrets out of"
" swap.\n"
"If you are running in a container or jail, the"
" privilege must be granted:\n"
" FreeBSD jail: set allow.mlock=1 for the jail\n"
" Linux: raise RLIMIT_MEMLOCK (ulimit -l), or grant"
" the CAP_IPC_LOCK capability\n"
" Docker/Podman: --ulimit memlock=-1:-1 or"
" --cap-add=IPC_LOCK",
tal_bytelen(ptr), strerror(errno));
abort();
}
tal_add_destructor(ptr, destroy_munlock);
}

Expand Down