From 6dbaed693a2497e06292ad12b0c7dfea10e087b3 Mon Sep 17 00:00:00 2001 From: DJ Delorie Date: Thu, 7 Aug 2025 17:07:53 -0400 Subject: [PATCH] login: fix ut_line comparison logic ut_line[] is not a string, it's a fixed-width character field, and may not be NUL terminated. Thus, the use of strcmp is incorrect. strncmp is more appropriate as it stops at the field size. Note that differences beyond the field size do not count here, as (1) this test doesn't do that, and (2) such differences are traditionally ignored (i.e. logins that are silently truncated to 8 characters, etc) While this is "only a test", we should still demonstrate the correct way of doing things. Also, using strncmp avoids a "not a string" warning from gcc if you use -O1 or lower, where it can't deduce that overflow won't happen. Reviewed-by: Sam James Reviewed-by: Collin Funk --- login/tst-utmp.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/login/tst-utmp.c b/login/tst-utmp.c index f2dbf9415e..d931e30de0 100644 --- a/login/tst-utmp.c +++ b/login/tst-utmp.c @@ -33,6 +33,7 @@ # define getutline getutxline # define getutid getutxid # define pututline pututxline +# define UT_LINESIZE __UT_LINESIZE #else # include #endif @@ -153,7 +154,7 @@ simulate_login (const char *line, const char *user) for (n = 0; n < num_entries; n++) { - if (strcmp (line, entry[n].ut_line) == 0 + if (strncmp (line, entry[n].ut_line, UT_LINESIZE) == 0 || entry[n].ut_type == DEAD_PROCESS) { if (entry[n].ut_pid == DEAD_PROCESS) @@ -186,7 +187,7 @@ simulate_logout (const char *line) for (n = 0; n < num_entries; n++) { - if (strcmp (line, entry[n].ut_line) == 0) + if (strncmp (line, entry[n].ut_line, UT_LINESIZE) == 0) { entry[n].ut_type = DEAD_PROCESS; strncpy (entry[n].ut_user, "", sizeof (entry[n].ut_user)); @@ -230,7 +231,7 @@ check_login (const char *line) for (n = 0; n < num_entries; n++) { - if (strcmp (line, entry[n].ut_line) == 0) + if (strncmp (line, entry[n].ut_line, UT_LINESIZE) == 0) { if (memcmp (up, &entry[n], sizeof (struct utmp))) { @@ -287,7 +288,7 @@ check_id (const char *id) for (n = 0; n < num_entries; n++) { - if (strcmp (id, entry[n].ut_id) == 0) + if (strncmp (id, entry[n].ut_id, sizeof (entry[n].ut_id)) == 0) { if (memcmp (up, &entry[n], sizeof (struct utmp))) { -- 2.47.3