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Simplify is_my_tty()

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This commit will serve to document why we shouldn't worry about the
truncation in the call to strlcpy(3).  Since we have one more byte in
tmptty than in full_tty, truncation will produce a string that is at
least one byte longer than full_tty.  Such a string could never compare
equal, so we're actually handling the truncation in a clever way.  Maybe
too clever, but that's why I'm documenting it here.

Now, about the simplification itself:

Since we made sure that both full_tty and tmptty are null-terminated, we
can call strcmp(3) instead of strncmp(3).  We can also simplify the
return logic avoiding one branch.

Cc: Paul Eggert <eggert@cs.ucla.edu>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
This commit is contained in:
Alejandro Colomar 2023-03-13 00:59:22 +01:00 committed by Iker Pedrosa
parent e27ca53091
commit 1d7d94ed7d
1 changed files with 4 additions and 6 deletions
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10
libmisc/utmp.c
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@ -32,7 +32,7 @@ static bool is_my_tty (const char tty[UT_LINESIZE])
{ {
char full_tty[STRLEN("/dev/") + UT_LINESIZE + 1]; char full_tty[STRLEN("/dev/") + UT_LINESIZE + 1];
/* tmptty shall be bigger than full_tty */ /* tmptty shall be bigger than full_tty */
static char tmptty[sizeof (full_tty)+1]; static char tmptty[sizeof(full_tty) + 1];
full_tty[0] = '\0'; full_tty[0] = '\0';
if (tty[0] != '/') if (tty[0] != '/')
@ -42,17 +42,15 @@ static bool is_my_tty (const char tty[UT_LINESIZE])
if ('\0' == tmptty[0]) { if ('\0' == tmptty[0]) {
const char *tname = ttyname (STDIN_FILENO); const char *tname = ttyname (STDIN_FILENO);
if (NULL != tname) if (NULL != tname)
(void) strlcpy (tmptty, tname, sizeof tmptty); (void) strlcpy (tmptty, tname, sizeof(tmptty));
} }
if ('\0' == tmptty[0]) { if ('\0' == tmptty[0]) {
(void) puts (_("Unable to determine your tty name.")); (void) puts (_("Unable to determine your tty name."));
exit (EXIT_FAILURE); exit (EXIT_FAILURE);
} else if (strncmp (full_tty, tmptty, sizeof (tmptty)) != 0) {
return false;
} else {
return true;
} }
return strcmp (full_tty, tmptty) == 0;
} }
/* /*