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elf: Remove /etc/suid-debug support

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Since malloc debug support moved to a different library
(libc_malloc_debug.so), the glibc.malloc.check requires preloading the
debug library to enable it.  It means that suid-debug support has not
been working since 2.34.

To restore its support, it would require to add additional information
and parsing to where to find libc_malloc_debug.so.

It is one thing less that might change AT_SECURE binaries' behavior
due to environment configurations.

Checked on x86_64-linux-gnu.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This commit is contained in:
Adhemerval Zanella 2023-11-06 17:25:34 -03:00
parent 64e4acf24d
commit 6c6fce572f
4 changed files with 3 additions and 24 deletions
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16
elf/dl-tunables.c
View file

@ -252,20 +252,6 @@ parse_tunables (char *tunestr, char *valstring)
tunestr[off] = '\0'; tunestr[off] = '\0';
} }
/* Enable the glibc.malloc.check tunable in SETUID/SETGID programs only when
the system administrator has created the /etc/suid-debug file. This is a
special case where we want to conditionally enable/disable a tunable even
for setuid binaries. We use the special version of access() to avoid
setting ERRNO, which is a TLS variable since TLS has not yet been set
up. */
static __always_inline void
maybe_enable_malloc_check (void)
{
tunable_id_t id = TUNABLE_ENUM_NAME (glibc, malloc, check);
if (__libc_enable_secure && __access_noerrno ("/etc/suid-debug", F_OK) == 0)
tunable_list[id].security_level = TUNABLE_SECLEVEL_NONE;
}
/* Initialize the tunables list from the environment. For now we only use the /* Initialize the tunables list from the environment. For now we only use the
ENV_ALIAS to find values. Later we will also use the tunable names to find ENV_ALIAS to find values. Later we will also use the tunable names to find
values. */ values. */
@ -277,8 +263,6 @@ __tunables_init (char **envp)
size_t len = 0; size_t len = 0;
char **prev_envp = envp; char **prev_envp = envp;
maybe_enable_malloc_check ();
while ((envp = get_next_env (envp, &envname, &len, &envval, while ((envp = get_next_env (envp, &envname, &len, &envval,
&prev_envp)) != NULL) &prev_envp)) != NULL)
{ {

3
elf/rtld.c
View file

@ -2670,8 +2670,7 @@ process_envvars (struct dl_main_state *state)
} }
while (*nextp != '\0'); while (*nextp != '\0');
if (__access ("/etc/suid-debug", F_OK) != 0) GLRO(dl_debug_mask) = 0;
GLRO(dl_debug_mask) = 0;
if (state->mode != rtld_mode_normal) if (state->mode != rtld_mode_normal)
_exit (5); _exit (5);

4
manual/memory.texi
View file

@ -1379,9 +1379,7 @@ There is one problem with @code{MALLOC_CHECK_}: in SUID or SGID binaries
it could possibly be exploited since diverging from the normal programs it could possibly be exploited since diverging from the normal programs
behavior it now writes something to the standard error descriptor. behavior it now writes something to the standard error descriptor.
Therefore the use of @code{MALLOC_CHECK_} is disabled by default for Therefore the use of @code{MALLOC_CHECK_} is disabled by default for
SUID and SGID binaries. It can be enabled again by the system SUID and SGID binaries.
administrator by adding a file @file{/etc/suid-debug} (the content is
not important it could be empty).
So, what's the difference between using @code{MALLOC_CHECK_} and linking So, what's the difference between using @code{MALLOC_CHECK_} and linking
with @samp{-lmcheck}? @code{MALLOC_CHECK_} is orthogonal with respect to with @samp{-lmcheck}? @code{MALLOC_CHECK_} is orthogonal with respect to

4
manual/tunables.texi
View file

@ -136,9 +136,7 @@ termination of the process.
Like @env{MALLOC_CHECK_}, @code{glibc.malloc.check} has a problem in that it Like @env{MALLOC_CHECK_}, @code{glibc.malloc.check} has a problem in that it
diverges from normal program behavior by writing to @code{stderr}, which could diverges from normal program behavior by writing to @code{stderr}, which could
by exploited in SUID and SGID binaries. Therefore, @code{glibc.malloc.check} by exploited in SUID and SGID binaries. Therefore, @code{glibc.malloc.check}
is disabled by default for SUID and SGID binaries. This can be enabled again is disabled by default for SUID and SGID binaries.
by the system administrator by adding a file @file{/etc/suid-debug}; the
content of the file could be anything or even empty.
@end deftp @end deftp
@deftp Tunable glibc.malloc.top_pad @deftp Tunable glibc.malloc.top_pad