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tunables: Terminate if end of input is reached (CVE-2023-4911)

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The string parsing routine may end up writing beyond bounds of tunestr
if the input tunable string is malformed, of the form name=name=val.
This gets processed twice, first as name=name=val and next as name=val,
resulting in tunestr being name=name=val:name=val, thus overflowing
tunestr.

Terminate the parsing loop at the first instance itself so that tunestr
does not overflow.

This also fixes up tst-env-setuid-tunables to actually handle failures
correct and add new tests to validate the fix for this CVE.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
(cherry picked from commit 1056e5b4c3)
This commit is contained in:
Siddhesh Poyarekar 2023-09-19 18:39:32 -04:00
parent 32957eb6a8
commit 22955ad851
3 changed files with 44 additions and 15 deletions
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5
NEWS
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@ -36,6 +36,11 @@ Security related changes:
an application calls getaddrinfo for AF_INET6 with AI_CANONNAME,
AI_ALL and AI_V4MAPPED flags set.
CVE-2023-4911: If a tunable of the form NAME=NAME=VAL is passed in the
environment of a setuid program and NAME is valid, it may result in a
buffer overflow, which could be exploited to achieve escalated
privileges. This flaw was introduced in glibc 2.34.
The following bugs are resolved with this release:
[12154] Do not fail DNS resolution for CNAMEs which are not host names

15
elf/dl-tunables.c
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@ -187,11 +187,7 @@ parse_tunables (char *tunestr, char *valstring)
/* If we reach the end of the string before getting a valid name-value
pair, bail out. */
if (p[len] == '\0')
{
if (__libc_enable_secure)
tunestr[off] = '\0';
return;
}
break;
/* We did not find a valid name-value pair before encountering the
colon. */
@ -251,9 +247,16 @@ parse_tunables (char *tunestr, char *valstring)
}
}
if (p[len] != '\0')
/* We reached the end while processing the tunable string. */
if (p[len] == '\0')
break;
p += len + 1;
}
/* Terminate tunestr before we leave. */
if (__libc_enable_secure)
tunestr[off] = '\0';
}
#endif

37
elf/tst-env-setuid-tunables.c
View File

@ -52,6 +52,8 @@ const char *teststrings[] =
"glibc.malloc.perturb=0x800:not_valid.malloc.check=2:glibc.malloc.mmap_threshold=4096",
"glibc.not_valid.check=2:glibc.malloc.mmap_threshold=4096",
"not_valid.malloc.check=2:glibc.malloc.mmap_threshold=4096",
"glibc.malloc.mmap_threshold=glibc.malloc.mmap_threshold=4096",
"glibc.malloc.check=2",
"glibc.malloc.garbage=2:glibc.maoc.mmap_threshold=4096:glibc.malloc.check=2",
"glibc.malloc.check=4:glibc.malloc.garbage=2:glibc.maoc.mmap_threshold=4096",
":glibc.malloc.garbage=2:glibc.malloc.check=1",
@ -70,6 +72,8 @@ const char *resultstrings[] =
"glibc.malloc.perturb=0x800:glibc.malloc.mmap_threshold=4096",
"glibc.malloc.mmap_threshold=4096",
"glibc.malloc.mmap_threshold=4096",
"glibc.malloc.mmap_threshold=glibc.malloc.mmap_threshold=4096",
"",
"",
"",
"",
@ -84,11 +88,18 @@ test_child (int off)
const char *val = getenv ("GLIBC_TUNABLES");
#if HAVE_TUNABLES
printf (" [%d] GLIBC_TUNABLES is %s\n", off, val);
fflush (stdout);
if (val != NULL && strcmp (val, resultstrings[off]) == 0)
return 0;
if (val != NULL)
printf ("[%d] Unexpected GLIBC_TUNABLES VALUE %s\n", off, val);
printf (" [%d] Unexpected GLIBC_TUNABLES VALUE %s, expected %s\n",
off, val, resultstrings[off]);
else
printf (" [%d] GLIBC_TUNABLES environment variable absent\n", off);
fflush (stdout);
return 1;
#else
@ -117,21 +128,26 @@ do_test (int argc, char **argv)
if (ret != 0)
exit (1);
exit (EXIT_SUCCESS);
/* Special return code to make sure that the child executed all the way
through. */
exit (42);
}
else
{
int ret = 0;
/* Spawn tests. */
for (int i = 0; i < array_length (teststrings); i++)
{
char buf[INT_BUFSIZE_BOUND (int)];
printf ("Spawned test for %s (%d)\n", teststrings[i], i);
printf ("[%d] Spawned test for %s\n", i, teststrings[i]);
snprintf (buf, sizeof (buf), "%d\n", i);
fflush (stdout);
if (setenv ("GLIBC_TUNABLES", teststrings[i], 1) != 0)
exit (1);
{
printf (" [%d] Failed to set GLIBC_TUNABLES: %m", i);
support_record_failure ();
continue;
}
int status = support_capture_subprogram_self_sgid (buf);
@ -139,9 +155,14 @@ do_test (int argc, char **argv)
if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
return EXIT_UNSUPPORTED;
ret |= status;
if (WEXITSTATUS (status) != 42)
{
printf (" [%d] child failed with status %d\n", i,
WEXITSTATUS (status));
support_record_failure ();
}
return ret;
}
return 0;
}
}