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From f435f80b9ae88caf9fe8af2e9b705dc8296ad6f3 Mon Sep 17 00:00:00 2001
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From: Karel Zak <kzak@redhat.com>
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Date: Mon, 13 Feb 2023 16:22:23 +0100
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Subject: last: use full size of the username
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utmp uses 32 bytes for username, last(1) truncates it to 31 when calls getpwnam().
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Reported-by: Radka Skvarilova <rskvaril@redhat.com>
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Signed-off-by: Karel Zak <kzak@redhat.com>
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Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=2160321
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Upstream: http://github.com/util-linux/util-linux/commit/4b646f01600a5efcf16e8e8991010b49b250bdfe
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---
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 login-utils/last.1 | 4 ++++
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 login-utils/last.c | 6 ++++--
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 2 files changed, 8 insertions(+), 2 deletions(-)
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diff --git a/login-utils/last.1 b/login-utils/last.1
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index 94b4ed012..9169abd35 100644
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--- a/login-utils/last.1
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+++ b/login-utils/last.1
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@@ -178,6 +178,10 @@ files to be used, they can be created with a simple
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 .BR touch (1)
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 command (for example,
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 .IR "touch /var/log/wtmp" ).
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+
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+The utmp file format uses fixed sizes of strings, which means that very long strings are
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+impossible to store in the file and impossible to display by last. The usual limits are 32
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+bytes for a user and line name and 256 bytes for a hostname.
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 .SH FILES
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 /var/log/wtmp
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 .br
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diff --git a/login-utils/last.c b/login-utils/last.c
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index 8f7c36984..41ce03894 100644
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--- a/login-utils/last.c
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+++ b/login-utils/last.c
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@@ -602,12 +602,14 @@ static int is_phantom(const struct last_control *ctl, struct utmpx *ut)
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 {
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 	struct passwd *pw;
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 	char path[sizeof(ut->ut_line) + 16];
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+	char user[sizeof(ut->ut_user) + 1];
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 	int ret = 0;
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 	if (ut->ut_tv.tv_sec < ctl->boot_time.tv_sec)
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 		return 1;
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-	ut->ut_user[sizeof(ut->ut_user) - 1] = '\0';
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-	pw = getpwnam(ut->ut_user);
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+
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+	mem2strcpy(user, ut->ut_user, sizeof(ut->ut_user), sizeof(user));
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+	pw = getpwnam(user);
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 	if (!pw)
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 		return 1;
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 	snprintf(path, sizeof(path), "/proc/%u/loginuid", ut->ut_pid);
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-- 
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2.39.1
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