[PATCH v5 4/4] Add system-wide tunables: Filters
DJ Delorie
dj@redhat.com
Wed Feb 11 04:33:51 GMT 2026
Add support for [proc:*] syntax where * matches /proc/self/exe
(fallback: argv[0]). Tunables after such a line are limited to
matching processes.
Note that this filter is reset when including a file or at
end of file.
If the filename starts with a slash (example: [proc:/bin/foo]) the
full path must match. If not (example: [proc:foo]) the basename is
matched.
---
csu/libc-start.c | 2 +-
elf/Makefile | 4 +
elf/cache.c | 3 +-
elf/dl-tunables.c | 68 ++++++++++++++++-
elf/dl-tunables.h | 2 +-
elf/tst-tunconf1.c | 36 +++++++++
elf/tst-tunconf1.root/etc/tunables.conf | 6 ++
elf/tst-tunconf1.root/ldconfig.run | 0
elf/tst-tunconf1.root/postclean.req | 0
elf/tunconf.c | 97 ++++++++++++++++++++++++-
sysdeps/mach/hurd/dl-sysdep.c | 2 +-
sysdeps/unix/sysv/linux/dl-sysdep.c | 2 +-
12 files changed, 210 insertions(+), 12 deletions(-)
create mode 100644 elf/tst-tunconf1.c
create mode 100644 elf/tst-tunconf1.root/etc/tunables.conf
create mode 100644 elf/tst-tunconf1.root/ldconfig.run
create mode 100644 elf/tst-tunconf1.root/postclean.req
diff --git a/csu/libc-start.c b/csu/libc-start.c
index 1c58561bce..ae36170045 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -264,7 +264,7 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
_dl_aux_init (auxvec);
# endif
- __tunables_init (__environ);
+ __tunables_init (__environ, argv);
ARCH_INIT_CPU_FEATURES ();
diff --git a/elf/Makefile b/elf/Makefile
index 282af88e71..b407e9e761 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -329,6 +329,7 @@ tests-internal := \
$(tests-static-internal) \
tst-tls1 \
tst-tls_tp_offset \
+ tst-tunconf1 \
# tests-internal
tests-static := $(tests-static-normal) $(tests-static-internal)
@@ -339,6 +340,8 @@ tests-static += \
tst-tls9-static \
# tests-static
+tst-tunconf1-ENV = GLIBC_TUNABLES=glibc.malloc.tcache_count=5
+
static-dlopen-environment = \
LD_LIBRARY_PATH=$(ld-library-path):$(common-objpfx)dlfcn
tst-tls9-static-ENV = $(static-dlopen-environment)
@@ -568,6 +571,7 @@ tests-container += \
tst-pldd \
tst-preload-pthread-libc \
tst-rootdir \
+ tst-tunconf1 \
# tests-container
test-srcs = \
diff --git a/elf/cache.c b/elf/cache.c
index e798f7e2d8..2809f255f5 100644
--- a/elf/cache.c
+++ b/elf/cache.c
@@ -300,9 +300,10 @@ print_extensions (struct cache_extension_all_loaded *ext,
thc->signature, thc->version, thc->num_tunables);
for (i = 0; i < count; ++ i)
{
- printf(" [%d] %s : %s [flags 0x%08x",
+ printf(" [%d] %s (%d) : %s [flags 0x%08x",
i,
cache_data + tec[i].name_offset,
+ tec[i].tunable_id,
cache_data + tec[i].value_offset,
tec[i].flags);
if (tec[i].flag_offset != 0)
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 83808f75e7..4637f47875 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -301,13 +301,22 @@ parse_tunables (const char *valstring)
ENV_ALIAS to find values. Later we will also use the tunable names to find
values. */
void
-__tunables_init (char **envp)
+__tunables_init (char **envp, char **argv)
{
char *envname = NULL;
char *envval = NULL;
char **prev_envp = envp;
#if defined(SHARED) && defined (USE_LDCONFIG)
+ const char *prog_name = (argv && argv[0]) ? argv[0] : "";
+ int prog_name_len = -1;
+ const char *base_name = NULL;
+ int base_name_len = -1;
+#ifdef PATH_MAX
+ char exebuf[PATH_MAX];
+#else
+ char exebuf[256];
+#endif
const struct tunable_header_cached *thc;
const char *td;
@@ -340,9 +349,58 @@ __tunables_init (char **envp)
if (tid == -1)
continue;
}
- /* At this point, TID is valid for the tunable we want. See
- if the parsed type matches the desired type. */
-
+ /* At this point, TID is valid for the tunable we want. */
+
+ /* Apply selected filter, if any. */
+ switch (tec->flags & TUNCONF_FLAG_FILTER) {
+ case TUNCONF_FILTER_PERPROC:
+ /* Perform one-time calculations that aren't needed if we
+ don't use this filter. */
+ if (prog_name_len == -1)
+ {
+ ssize_t n = readlink ("/proc/self/exe",
+ exebuf, sizeof (exebuf) - 1);
+ if (n > 0 && n < sizeof(exebuf)-1)
+ {
+ /* If /proc/self/exe exists and we can read it,
+ it's more reliable than argv[] so use it. */
+ exebuf[n] = '\0';
+ prog_name = exebuf;
+ }
+ if (prog_name != NULL)
+ {
+ const char *slash = NULL, *cp;
+ for (cp = prog_name; *cp; ++ cp)
+ if (*cp == '/')
+ slash = cp;
+ if (slash)
+ base_name = slash + 1;
+ else
+ base_name = prog_name;
+ prog_name_len = strlen (prog_name);
+ base_name_len = strlen (base_name);
+ }
+ }
+ /* prog_name and the cached string are both NUL terminated. */
+ if (prog_name)
+ {
+ if (((const char *)(td + tec->flag_offset))[0] == '/')
+ {
+ if (memcmp (prog_name, td + tec->flag_offset, prog_name_len) != 0)
+ goto skip_due_to_filter;
+ }
+ else
+ {
+ if (memcmp (base_name, td + tec->flag_offset, base_name_len) != 0)
+ goto skip_due_to_filter;
+ }
+ }
+ break;
+ default:
+ break;
+ }
+
+ /* See if the parsed type matches the desired type. */
if (tunable_list[tid].type.type_code == TUNABLE_TYPE_STRING)
{
/* This is a memory leak but there's no easy way around
@@ -365,6 +423,8 @@ __tunables_init (char **envp)
value, strlen (value));
}
}
+
+ skip_due_to_filter:
}
}
#endif
diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
index 45aeed47bc..3f34329614 100644
--- a/elf/dl-tunables.h
+++ b/elf/dl-tunables.h
@@ -47,7 +47,7 @@ typedef void (*tunable_callback_t) (tunable_val_t *);
#include "dl-tunable-list.h"
-extern void __tunables_init (char **);
+extern void __tunables_init (char **, char **);
extern void __tunables_print (void);
extern bool __tunable_is_initialized (tunable_id_t);
extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
diff --git a/elf/tst-tunconf1.c b/elf/tst-tunconf1.c
new file mode 100644
index 0000000000..c95a7cb8ba
--- /dev/null
+++ b/elf/tst-tunconf1.c
@@ -0,0 +1,36 @@
+/* Test that the tunables cache can override env vars.
+ Copyright (C) 2026 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <stdio.h>
+#include <support/check.h>
+
+#include "dl-tunables.h"
+
+static int
+do_test (void)
+{
+ size_t tcache_count = TUNABLE_GET_FULL (glibc, malloc, tcache_count, size_t, NULL);
+ size_t tcache_max = TUNABLE_GET_FULL (glibc, malloc, tcache_max, size_t, NULL);
+ printf("tcache count is %ld (should be 5, from env)\n", (long)tcache_count);
+ TEST_COMPARE ((long)tcache_count, 5);
+ printf("tcache max is %ld (should be 4, from /etc)\n", (long)tcache_max);
+ TEST_COMPARE ((long)tcache_max, 4);
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/elf/tst-tunconf1.root/etc/tunables.conf b/elf/tst-tunconf1.root/etc/tunables.conf
new file mode 100644
index 0000000000..3c7b33c399
--- /dev/null
+++ b/elf/tst-tunconf1.root/etc/tunables.conf
@@ -0,0 +1,6 @@
+glibc.malloc.tcache_max=6
+glibc.malloc.tcache_count=3
+[proc:/bin/ls]
+glibc.malloc.tcache_max=7
+[proc:tst-tunconf1]
+glibc.malloc.tcache_max=4
diff --git a/elf/tst-tunconf1.root/ldconfig.run b/elf/tst-tunconf1.root/ldconfig.run
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/elf/tst-tunconf1.root/postclean.req b/elf/tst-tunconf1.root/postclean.req
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/elf/tunconf.c b/elf/tunconf.c
index ea547e95d5..cb26d47816 100644
--- a/elf/tunconf.c
+++ b/elf/tunconf.c
@@ -65,12 +65,14 @@ typedef enum {
struct tunable_entry_int {
struct stringtable_entry *name;
struct stringtable_entry *value;
+ struct stringtable_entry *filter;
TOP top;
int tunable_id;
int value_is_negative:1;
int value_was_parsed:1;
unsigned long long value_ull;
signed long long value_sll;
+ long filter_flags;
struct tunable_entry_int *next;
};
@@ -78,11 +80,80 @@ struct tunable_entry_int {
struct tunable_entry_int *entry_list;
struct tunable_entry_int **entry_list_next = &entry_list;
+static int filter_flags = 0;
+static char *filter_string = NULL;
+
/*----------------------------------------------------------------------*/
static void parse_tunconf_include (const char *tunconfig_file, unsigned int lineno,
bool do_chroot, const char *pattern, const char *opt_chroot);
+
+static void
+clear_filter (void)
+{
+ free (filter_string);
+ filter_string = NULL;
+ filter_flags = 0;
+}
+
+/* Filters are lines the are bracketed, like
+ [prog:foo]
+*/
+static void
+parse_filter (char *line, const char *filename, int lineno)
+{
+ const char *colon = NULL;
+ const char *right_bracket = NULL;
+ const char *cp;
+
+ for (cp=line; *cp != 0; cp++)
+ {
+ if (*cp == ':')
+ colon = cp;
+ if (*cp == ']')
+ {
+ right_bracket = cp;
+ break;
+ }
+ }
+ /* Special case: [] means "no filter" */
+ if (right_bracket != NULL && right_bracket == line + 1)
+ {
+ clear_filter ();
+ return;
+ }
+ if (colon == NULL)
+ {
+ printf("%s:%d: syntax error, filter line ignored: `%s' (missing ':')\n",
+ filename, lineno, line);
+ return;
+ }
+ if (right_bracket == NULL)
+ {
+ printf("%s:%d: syntax error, filter line ignored: `%s' (missing ']')\n",
+ filename, lineno, line);
+ return;
+ }
+
+ if (filter_string != NULL)
+ {
+ clear_filter ();
+ }
+
+ if (memcmp ("proc", line + 1, colon - line - 1) == 0)
+ {
+ filter_string = (char *) malloc (right_bracket - colon);
+ memcpy (filter_string, colon + 1, right_bracket - colon - 1);
+ filter_string [right_bracket - colon] = 0;
+ filter_flags = TUNCONF_FILTER_PERPROC;
+ }
+
+ else
+ printf("%s:%d: unrecognized filter `%.*s', ignored\n", filename, lineno, (int)(colon - line - 1), line + 1);
+}
+
+
static void
add_tunable (char *line, const char *filename, int lineno)
{
@@ -98,7 +169,7 @@ add_tunable (char *line, const char *filename, int lineno)
/* Leading whitespace has already been stripped. */
- if (*line == '!' || *line == '+' || *line == '-')
+ if (*line == '!' || *line == '+' || *line == '-' || *line == '[')
{
switch (*line)
{
@@ -111,8 +182,10 @@ add_tunable (char *line, const char *filename, int lineno)
case '-':
top = TOP_DENY;
break;
+ case '[':
+ parse_filter (line, filename, lineno);
+ return;
}
- printf("TOP: %d\n", top);
line ++;
while (*line && isspace(*line))
line ++;
@@ -175,6 +248,12 @@ add_tunable (char *line, const char *filename, int lineno)
entry->tunable_id = id;
entry->top = top;
+ if (filter_flags)
+ {
+ entry->filter_flags = filter_flags;
+ entry->filter = cache_store_string (filter_string);
+ }
+
*entry_list_next = entry;
entry_list_next = & (entry->next);
}
@@ -188,6 +267,9 @@ parse_tunconf (const char *filename, int do_chroot, char *opt_chroot)
size_t len = 0;
unsigned int lineno;
+ /* Filters do not live across file boundaries. */
+ clear_filter ();
+
if (do_chroot && opt_chroot)
{
canon = chroot_canon (opt_chroot, filename);
@@ -259,6 +341,7 @@ Warning: ignoring configuration file that cannot be opened: %s"),
/* Free buffer and close file. */
free (line);
fclose (file);
+ clear_filter ();
}
/* Handle one word in an `include' line, a glob pattern of additional
@@ -388,7 +471,15 @@ get_tunconf_ext (uint32_t string_table_offset)
tec->tunable_id = tei->tunable_id;
tec->name_offset = tei->name->offset + string_table_offset;
tec->value_offset = tei->value->offset + string_table_offset;
- tec->flag_offset = 0;
+
+ if (tei->filter_flags != 0)
+ {
+ tec->flag_offset = tei->filter->offset + string_table_offset;
+ tec->flags |= tei->filter_flags;
+ }
+ else
+ tec->flag_offset = 0;
+
tec->unused_1 = 0;
if (tei->value_is_negative)
tec->parsed_value = (uint64_t) tei->value_sll;
diff --git a/sysdeps/mach/hurd/dl-sysdep.c b/sysdeps/mach/hurd/dl-sysdep.c
index 0e348d6440..fe6d453756 100644
--- a/sysdeps/mach/hurd/dl-sysdep.c
+++ b/sysdeps/mach/hurd/dl-sysdep.c
@@ -98,7 +98,7 @@ _dl_sysdep_start (void **start_argptr,
__libc_enable_secure = _dl_hurd_data->flags & EXEC_SECURE;
- __tunables_init (_environ);
+ __tunables_init (_environ, _dl_argv);
/* Initialize DSO sorting algorithm after tunables. */
_dl_sort_maps_init ();
diff --git a/sysdeps/unix/sysv/linux/dl-sysdep.c b/sysdeps/unix/sysv/linux/dl-sysdep.c
index cb1f94ee23..c2701f274c 100644
--- a/sysdeps/unix/sysv/linux/dl-sysdep.c
+++ b/sysdeps/unix/sysv/linux/dl-sysdep.c
@@ -107,7 +107,7 @@ _dl_sysdep_start (void **start_argptr,
dl_hwcap_check ();
- __tunables_init (_environ);
+ __tunables_init (_environ, (char **) (start_argptr + 1));
/* Initialize DSO sorting algorithm after tunables. */
_dl_sort_maps_init ();
--
2.47.3
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