nt->buf is exactly MAX_PRINT_CHUNK bytes, but scnprintf() reserves one byte for its NUL terminator, so a non-fragmented payload of exactly MAX_PRINT_CHUNK loses its last byte (emitted as a stray NUL in the release path). Grow nt->buf to MAX_PRINT_CHUNK + 1 and bound the scnprintf() calls with sizeof(nt->buf); the transmitted length stays capped at MAX_PRINT_CHUNK. Alternatively, nt->buf could be left at MAX_PRINT_CHUNK and the NUL byte reserved by routing exactly-MAX_PRINT_CHUNK payloads to fragmentation ('len < MAX_PRINT_CHUNK'), at the cost of fragmenting those messages. But it would look less sane, thus the current approach. Fixes: c62c0a17f9b7 ("netconsole: Append kernel version to message") Signed-off-by: Breno Leitao --- drivers/net/netconsole.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c index 57dd6821a8aa9..bfab0a47678c9 100644 --- a/drivers/net/netconsole.c +++ b/drivers/net/netconsole.c @@ -184,8 +184,10 @@ struct netconsole_target { bool extended; bool release; struct netpoll np; - /* protected by target_list_lock */ - char buf[MAX_PRINT_CHUNK]; + /* protected by target_list_lock; +1 gives scnprintf() room for its + * NUL terminator so a full MAX_PRINT_CHUNK payload is not truncated + */ + char buf[MAX_PRINT_CHUNK + 1]; struct work_struct resume_wq; }; @@ -1692,7 +1694,7 @@ static void send_msg_no_fragmentation(struct netconsole_target *nt, if (release_len) { release = init_utsname()->release; - scnprintf(nt->buf, MAX_PRINT_CHUNK, "%s,%.*s", release, + scnprintf(nt->buf, sizeof(nt->buf), "%s,%.*s", release, msg_len, msg); msg_len += release_len; } else { @@ -1701,12 +1703,12 @@ static void send_msg_no_fragmentation(struct netconsole_target *nt, if (userdata) msg_len += scnprintf(&nt->buf[msg_len], - MAX_PRINT_CHUNK - msg_len, "%s", + sizeof(nt->buf) - msg_len, "%s", userdata); if (sysdata) msg_len += scnprintf(&nt->buf[msg_len], - MAX_PRINT_CHUNK - msg_len, "%s", + sizeof(nt->buf) - msg_len, "%s", sysdata); send_udp(nt, nt->buf, msg_len); --- base-commit: fbc6a80cb5d3fd4ac4b56e8c9d791dd17be890c4 change-id: 20260616-max_print_chunk-0a8cea1b1ed7 Best regards, -- Breno Leitao