libreboot-utils: stricter errno handling

where possible, try not to clobber sys errno. override
it only when relatively safe.

also: when a syscall succeeds, it may set errno. this
is rare, but permitted (nothing specified against it
in specs, and the specs say that errno is undefined
on success).

i'm not libc, but i'm wrapping around it, so i need
to be careful in how i handle the errno value.

also:

i removed the requirement for directories to be
executable, in mkhtemp.c, because this isn't required
and will only break certain setups.

in world_writeable and sticky, i made the checks stricter:
the faccessat check was being skipped on some paths, so
i've closed that loophole now.

i also generally cleaned up some code, as part of the errno
handling refactoring, where it made sense to do so, plus a
few other bits of code cleanup.

Signed-off-by: Leah Rowe <leah@libreboot.org>

1 files changed, 35 insertions, 19 deletions

diff --git a/util/libreboot-utils/lib/string.c b/util/libreboot-utils/lib/string.c
index ad11d29d..ce54a524 100644
--- a/util/libreboot-utils/lib/string.c
+++ b/util/libreboot-utils/lib/string.c
@@ -50,6 +50,7 @@ pagesize(void)
 {
 	static long rval = 0;
 	static int set = 0;
+	int saved_errno = 0;
 
 	if (!set) {
 		if ((rval = sysconf(_SC_PAGESIZE)) < 0)
@@ -57,6 +58,7 @@ pagesize(void)
 		set = 1;
 	}
 
+	reset_caller_errno(0);
 	return rval;
 }
 
@@ -92,7 +94,9 @@ smalloc(char **buf, size_t size)
 void *
 vmalloc(void **buf, size_t size)
 {
+	int saved_errno = errno;
 	void *rval = NULL;
+	errno = 0;
 
 	if (size >= SIZE_MAX - 1)
 		err_exit(EOVERFLOW, "integer overflow in vmalloc");
@@ -116,6 +120,7 @@ vmalloc(void **buf, size_t size)
 	if ((rval = malloc(size)) == NULL)
 		err_exit(errno, "malloc fail in vmalloc");
 
+	reset_caller_errno(0);
 	return *buf = rval;
 }
 
@@ -131,6 +136,7 @@ scmp(const char *a,
 	size_t wa;
 	size_t wb;
 	int saved_errno = errno;
+	errno = 0;
 
 	if (if_err(a == NULL || b == NULL || rval == NULL, EFAULT))
 		goto err;
@@ -171,14 +177,14 @@ scmp(const char *a,
 			goto out;
 
 err:
-	(void) set_errno(saved_errno, EFAULT);
+	(void) with_fallback_errno(EFAULT);
 	if (rval != NULL)
 		*rval = -1;
 
 	err_exit(errno, "scmp");
 	return -1;
 out:
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return *rval;
 }
 
@@ -215,13 +221,14 @@ slen(const char *s,
 	size_t i = 0;
 	size_t w;
 	size_t j;
+	errno = 0;
 
 	if (if_err(s == NULL || rval == NULL, EFAULT))
 		goto err;
 
 	for ( ; ((uintptr_t)(s + i) % sizeof(size_t)) != 0; i++) {
 
-		if (i >= maxlen)
+		if (if_err(i >= maxlen, EOVERFLOW))
 			goto err;
 		if (s[i] == '\0') {
 			*rval = i;
@@ -252,14 +259,14 @@ slen(const char *s,
 	}
 
 err:
-	(void) set_errno(saved_errno, EFAULT);
+	(void) with_fallback_errno(EFAULT);
 	if (rval != NULL)
 		*rval = 0;
 
 	err_exit(errno, "slen"); /* abort */
 	return 0; /* gcc15 is happy */
 out:
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return *rval;
 }
 
@@ -273,6 +280,7 @@ sdup(const char *s,
 	size_t i = 0;
 	char *out = NULL;
 	int saved_errno = errno;
+	errno = 0;
 
 	if (if_err(dest == NULL || *dest != NULL || s == NULL, EFAULT))
 		goto err;
@@ -326,12 +334,12 @@ err:
 	if (dest != NULL)
 		*dest = NULL;
 
-	(void) set_errno(saved_errno, EFAULT);
+	(void) with_fallback_errno(EFAULT);
 	err_exit(errno, "sdup");
 
 	return NULL;
 out:
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return *dest;
 }
 
@@ -345,6 +353,7 @@ scatn(ssize_t sc, const char **sv,
 	char *rcur = NULL;
 	char *rtmp = NULL;
 	size_t i;
+	errno = 0;
 
 	if (if_err(sc < 2, EINVAL) ||
 	    if_err(sv == NULL, EFAULT) ||
@@ -368,7 +377,7 @@ scatn(ssize_t sc, const char **sv,
 		rtmp = NULL;
 	}
 
-	errno = saved_errno;
+	reset_caller_errno(0);
 	*rval = final;
 	return *rval;
 err:
@@ -376,7 +385,7 @@ err:
 	free_and_set_null(&rtmp);
 	free_and_set_null(&final);
 
-	(void) set_errno(saved_errno, EFAULT);
+	(void) with_fallback_errno(EFAULT);
 
 	err_exit(errno, "scatn");
 	return NULL;
@@ -391,6 +400,7 @@ scat(const char *s1, const char *s2,
 	size_t size2;
 	char *rval = NULL;
 	int saved_errno = errno;
+	errno = 0;
 
 	if (if_err(dest == NULL || *dest != NULL, EFAULT))
 		goto err;
@@ -408,11 +418,11 @@ scat(const char *s1, const char *s2,
 	memcpy(rval + size1, s2, size2);
 	*(rval + size1 + size2) = '\0';
 
+	reset_caller_errno(0);
 	*dest = rval;
-	errno = saved_errno;
 	return *dest;
 err:
-	(void) set_errno(saved_errno, EINVAL);
+	(void) with_fallback_errno(EINVAL);
 	if (dest != NULL)
 		*dest = NULL;
 	err_exit(errno, "scat");
@@ -431,6 +441,7 @@ dcat(const char *s, size_t n,
 	char *rval1 = NULL;
 	char *rval2 = NULL;
 	int saved_errno = errno;
+	errno = 0;
 
 	if (if_err(dest1 == NULL || dest2 == NULL, EFAULT))
 		goto err;
@@ -450,7 +461,7 @@ dcat(const char *s, size_t n,
 	*dest1 = rval1;
 	*dest2 = rval2;
 
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return;
 
 err:
@@ -459,7 +470,7 @@ err:
 	free_and_set_null(&rval1);
 	free_and_set_null(&rval2);
 
-	(void) set_errno(saved_errno, EINVAL);
+	(void) with_fallback_errno(EINVAL);
 	err_exit(errno, "dcat");
 }
 
@@ -477,6 +488,7 @@ vcmp(const void *s1, const void *s2, size_t n)
 
 	const unsigned char *x;
 	const unsigned char *y;
+	errno = 0;
 
 	if (if_err(s1 == NULL || s2 == NULL, EFAULT))
 		err_exit(EFAULT, "vcmp: null input");
@@ -497,7 +509,7 @@ vcmp(const void *s1, const void *s2, size_t n)
 		if (x[i] != y[i])
 			return (int)x[i] - (int)y[i];
 
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return 0;
 }
 
@@ -507,9 +519,9 @@ vcmp(const void *s1, const void *s2, size_t n)
  * under error condition.
  */
 int
-set_errno(int saved_errno, int fallback)
+with_fallback_errno(int fallback)
 {
-	if (errno == saved_errno)
+	if (!errno)
 		errno = fallback;
 	return -1;
 }
@@ -525,7 +537,8 @@ err_exit(int nvm_errval, const char *msg, ...)
 
 	func_t err_cleanup = errhook(NULL);
 	err_cleanup();
-	errno = saved_errno;
+	reset_caller_errno(0);
+	saved_errno = errno;
 
 	if (!errno)
 		saved_errno = errno = ECANCELED;
@@ -536,6 +549,7 @@ err_exit(int nvm_errval, const char *msg, ...)
 	vfprintf(stderr, msg, args);
 	va_end(args);
 
+	errno = saved_errno;
 	fprintf(stderr, ": %s\n", strerror(errno));
 
 	exit(EXIT_FAILURE);
@@ -615,11 +629,12 @@ xpledgex(const char *promises, const char *execpromises)
 {
 	int saved_errno = errno;
 	(void) promises, (void) execpromises, (void) saved_errno;
+	errno = 0;
 #ifdef __OpenBSD__
 	if (pledge(promises, execpromises) == -1)
 		err_exit(errno, "pledge");
 #endif
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return 0;
 }
 int
@@ -627,10 +642,11 @@ xunveilx(const char *path, const char *permissions)
 {
 	int saved_errno = errno;
 	(void) path, (void) permissions, (void) saved_errno;
+	errno = 0;
 #ifdef __OpenBSD__
 	if (pledge(promises, execpromises) == -1)
 		err_exit(errno, "pledge");
 #endif
-	errno = saved_errno;
+	reset_caller_errno(0);
 	return 0;
 }