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libutil: Simplify util_path_sysfs and helper functions

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Using util_path_sysfs always leaves 5 bytes of memory unfreed as the
value for the sysfs mount point is stored in a static variable to avoid
multiple queries of /proc/mount.

$ valgrind ./util_path_example sysfs
==3629315== Memcheck, a memory error detector
==3629315== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3629315== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==3629315== Command: ./util_path_example sysfs
==3629315==
Path for    cpu: "/sys/devices/system/cpu"
Path for memory: "/sys/devices/system/memory"
==3629315==
==3629315== HEAP SUMMARY:
==3629315==     in use at exit: 5 bytes in 1 blocks
==3629315==   total heap usage: 22 allocs, 21 frees, 18,435 bytes allocated
==3629315==
==3629315== LEAK SUMMARY:
==3629315==    definitely lost: 0 bytes in 0 blocks
==3629315==    indirectly lost: 0 bytes in 0 blocks
==3629315==      possibly lost: 0 bytes in 0 blocks
==3629315==    still reachable: 5 bytes in 1 blocks
==3629315==         suppressed: 0 bytes in 0 blocks
==3629315== Rerun with --leak-check=full to see details of leaked memory
==3629315==
==3629315== For lists of detected and suppressed errors, rerun with: -s
==3629315== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

As per the Kernel rules for accessing sysfs information [1], searching
for the sysfs mount point is a waste of time and systems that don't have
sysfs mounted at /sys are considered broken.

With those things in mind, util_path_sysfs() and especially
sys_mount_point() can be simplified. sys_mount_point() will always
return '/sys' unless the environment variable SYSFS_ROOT is set.

With SYSFS_ROOT still being present, special container setups or test
case scenarios are still possible but might need to be modified if they
previously relied on util_path_sysfs() automatically finding the correct
sysfs mount point.

To make things more secure against malicious strings in SYSFS_ROOT,
secure_getenv() is being used and the ordering of creating the formatted
path string in util_path_sysfs() is changed slightly.

Furthermore, the static variable is removed as no complicated query of
the /proc fs is required anymore. Memory for the sysfs mount point value
is properly freed now at the end of util_path_sysfs().

[1] https://www.kernel.org/doc/html/latest/admin-guide/sysfs-rules.html
Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
This commit is contained in:
Jan Höppner
2021-06-17 23:00:56 +02:00
parent 3e818c53b2
commit 5e5d49264f
1 changed files with 16 additions and 23 deletions
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libutil/util_path.c
+16 -23
View File
@@ -20,7 +20,6 @@
#include "lib/util_libc.h"
#include "lib/util_path.h"
#include "lib/util_prg.h"
#include "lib/util_proc.h"
/*
* Verify that directory exists
@@ -39,28 +38,20 @@ static void verify_dir(const char *dir)
/*
* Return sysfs mount point
*
* The caller must free the memory for mount_point.
*/
static char *sys_mount_point(void)
static void sys_mount_point(char **mount_point)
{
struct util_proc_mnt_entry mnt_entry;
static char *mount_point;
char *dir;
if (mount_point)
return mount_point;
/* Check the environment variable */
dir = getenv("SYSFS_ROOT");
if (dir) {
mount_point = util_strdup(dir);
} else {
if (util_proc_mnt_get_entry("/proc/mounts", "sysfs",
&mnt_entry))
errx(EXIT_FAILURE, "No mount point found for sysfs");
mount_point = util_strdup(mnt_entry.file);
util_proc_mnt_free_entry(&mnt_entry);
}
verify_dir(mount_point);
return mount_point;
dir = secure_getenv("SYSFS_ROOT");
if (dir)
*mount_point = util_strdup(dir);
else
*mount_point = util_strdup("/sys");
verify_dir(*mount_point);
}
/**
@@ -76,15 +67,17 @@ static char *sys_mount_point(void)
*/
char *util_path_sysfs(const char *fmt, ...)
{
char *path, *fmt_tot;
char *path, *fmt_path, *sysfs;
va_list ap;
util_asprintf(&fmt_tot, "%s/%s", sys_mount_point(), fmt);
/* Format and return full sysfs path */
va_start(ap, fmt);
util_vasprintf(&path, fmt_tot, ap);
util_vasprintf(&fmt_path, fmt, ap);
va_end(ap);
free(fmt_tot);
sys_mount_point(&sysfs);
/* Format and return full sysfs path */
util_asprintf(&path, "%s/%s", sysfs, fmt_path);
free(fmt_path);
free(sysfs);
return path;
}