commit 76a7c103eb9060f9e3ba01d073ae4621a17d8b46

Author: Florian Weimer <fweimer@redhat.com>

Date:   Tue Nov 12 12:02:57 2019 +0100

    login: Introduce matches_last_entry to utmp processing

    This simplifies internal_getut_nolock and fixes a regression,

    introduced in commit be6b16d975683e6cca57852cd4cfe715b2a9d8b1

    ("login: Acquire write lock early in pututline [BZ #24882]")

    in pututxline because __utmp_equal can only compare process-related

    utmp entries.

    Fixes: be6b16d975683e6cca57852cd4cfe715b2a9d8b1

    Change-Id: Ib8a85002f7f87ee41590846d16d7e52bdb82f5a5

diff --git a/login/utmp_file.c b/login/utmp_file.c

index 6bba120db9cc574e..e653d14967c4fb7a 100644

--- a/login/utmp_file.c

+++ b/login/utmp_file.c

@@ -43,6 +43,25 @@ static off64_t file_offset;

 /* Cache for the last read entry.  */

 static struct utmp last_entry;

+/* Returns true if *ENTRY matches last_entry, based on

+   data->ut_type.  */

+static bool

+matches_last_entry (const struct utmp *data)

+{

+  if (file_offset <= 0)

+    /* Nothing has been read.  last_entry is stale and cannot match.  */

+    return false;

+

+  if (data->ut_type == RUN_LVL

+      || data->ut_type == BOOT_TIME

+      || data->ut_type == OLD_TIME

+      || data->ut_type == NEW_TIME)

+    /* For some entry types, only a type match is required.  */

+    return data->ut_type == last_entry.ut_type;

+  else

+    /* For the process-related entries, a full match is needed.  */

+    return __utmp_equal (&last_entry, data);

+}

 /* Locking timeout.  */

 #ifndef TIMEOUT

@@ -133,9 +152,6 @@ __libc_setutent (void)

   __lseek64 (file_fd, 0, SEEK_SET);

   file_offset = 0;

-  /* Make sure the entry won't match.  */

-  last_entry.ut_type = -1;

-

   return 1;

 }

@@ -191,48 +207,20 @@ __libc_getutent_r (struct utmp *buffer, struct utmp **result)

 static int

 internal_getut_nolock (const struct utmp *id)

 {

-  if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME

-      || id->ut_type == OLD_TIME || id->ut_type == NEW_TIME)

+  while (1)

     {

-      /* Search for next entry with type RUN_LVL, BOOT_TIME,

-	 OLD_TIME, or NEW_TIME.  */

-

-      while (1)

+      /* Read the next entry.  */

+      if (__read_nocancel (file_fd, &last_entry, sizeof (struct utmp))

+	  != sizeof (struct utmp))

 	{

-	  /* Read the next entry.  */

-	  if (__read_nocancel (file_fd, &last_entry, sizeof (struct utmp))

-	      != sizeof (struct utmp))

-	    {

-	      __set_errno (ESRCH);

-	      file_offset = -1l;

-	      return -1;

-	    }

-	  file_offset += sizeof (struct utmp);

-

-	  if (id->ut_type == last_entry.ut_type)

-	    break;

+	  __set_errno (ESRCH);

+	  file_offset = -1l;

+	  return -1;

 	}

-    }

-  else

-    {

-      /* Search for the next entry with the specified ID and with type

-	 INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS.  */

-

-      while (1)

-	{

-	  /* Read the next entry.  */

-	  if (__read_nocancel (file_fd, &last_entry, sizeof (struct utmp))

-	      != sizeof (struct utmp))

-	    {

-	      __set_errno (ESRCH);

-	      file_offset = -1l;

-	      return -1;

-	    }

-	  file_offset += sizeof (struct utmp);

+      file_offset += sizeof (struct utmp);

-	  if (__utmp_equal (&last_entry, id))

-	    break;

-	}

+      if (matches_last_entry (id))

+	break;

     }

   return 0;

@@ -365,13 +353,7 @@ __libc_pututline (const struct utmp *data)

   /* Find the correct place to insert the data.  */

   bool found = false;

-  if (file_offset > 0

-      && ((last_entry.ut_type == data->ut_type

-	   && (last_entry.ut_type == RUN_LVL

-	       || last_entry.ut_type == BOOT_TIME

-	       || last_entry.ut_type == OLD_TIME

-	       || last_entry.ut_type == NEW_TIME))

-	  || __utmp_equal (&last_entry, data)))

+  if (matches_last_entry (data))

     {

       if (__lseek64 (file_fd, file_offset, SEEK_SET) < 0)

 	{

@@ -389,7 +371,7 @@ __libc_pututline (const struct utmp *data)

 	  found = false;

 	}

       else

-	found = __utmp_equal (&last_entry, data);

+	found = matches_last_entry (data);

     }

   if (!found)