From 22955ad85186ee05834e47e665056148ca07699c Mon Sep 17 00:00:00 2001 From: Siddhesh Poyarekar Date: Tue, 19 Sep 2023 18:39:32 -0400 Subject: [PATCH] tunables: Terminate if end of input is reached (CVE-2023-4911) 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 Reviewed-by: Carlos O'Donell (cherry picked from commit 1056e5b4c3f2d90ed2b4a55f96add28da2f4c8fa) --- NEWS | 5 +++++ elf/dl-tunables.c | 17 +++++++++------- elf/tst-env-setuid-tunables.c | 37 +++++++++++++++++++++++++++-------- 3 files changed, 44 insertions(+), 15 deletions(-) diff --git a/NEWS b/NEWS index ae55ffb53a..5358e0cbe3 100644 --- a/NEWS +++ b/NEWS @@ -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 diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c index 8e7ee9df10..76cf8b9da3 100644 --- a/elf/dl-tunables.c +++ b/elf/dl-tunables.c @@ -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') - p += len + 1; + /* 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 diff --git a/elf/tst-env-setuid-tunables.c b/elf/tst-env-setuid-tunables.c index 88182b7b25..5e9e4c5756 100644 --- a/elf/tst-env-setuid-tunables.c +++ b/elf/tst-env-setuid-tunables.c @@ -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; } }