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login: Introduce matches_last_entry to utmp processing

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This simplifies internal_getut_nolock and fixes a regression,
introduced in commit be6b16d975
("login: Acquire write lock early in pututline [BZ #24882]")
in pututxline because __utmp_equal can only compare process-related
utmp entries.

Fixes: be6b16d975
Change-Id: Ib8a85002f7f87ee41590846d16d7e52bdb82f5a5
This commit is contained in:
Florian Weimer 2019-11-12 12:02:57 +01:00
parent cba932a5a9
commit 76a7c103eb
1 changed files with 31 additions and 49 deletions
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80
login/utmp_file.c
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@ -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. */
file_offset += sizeof (struct utmp);
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);
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)