nss: prevent PROTECT_ERRNO from squashing changes to *errnop

glibc passes in &errno for errnop, which means PROTECT_ERRNO ends up
squashing our intentional changes to *errnop.

Fixes #11321.

1 files changed, 22 insertions, 1 deletions

diff --git a/src/basic/util.h b/src/basic/util.h
index f009d37d4c..77ef1d9892 100644
--- a/src/basic/util.h
+++ b/src/basic/util.h
@@ -174,12 +174,33 @@ static inline void *mempset(void *s, int c, size_t n) {
 }
 
 static inline void _reset_errno_(int *saved_errno) {
-        errno = *saved_errno;
+        if (*saved_errno >= 0)
+                errno = *saved_errno;
 }
 
 #define PROTECT_ERRNO                                                   \
         _cleanup_(_reset_errno_) _unused_ int _saved_errno_ = errno
 
+/*
+ * NSS modules should indicate errors by assigning to the passed-in *errnop
+ * rather than errno directly; however in dynamically-linked programs, errnop
+ * == &errno, so PROTECT_ERRNO has to be disabled in order for assigning to
+ * *errnop to be effective.
+ */
+#define DISARM_PROTECT_ERRNO(r) \
+        ({ \
+                _reset_errno_(&_saved_errno_); \
+                _saved_errno_ = -1; \
+                abs(r); \
+        })
+
+#define DISARM_PROTECT_ERRNO_INNER(r) \
+        ({ \
+                _reset_errno_(_saved_errno_p); \
+                *_saved_errno_p = -1; \
+                abs(r); \
+        })
+
 static inline int negative_errno(void) {
         /* This helper should be used to shut up gcc if you know 'errno' is
          * negative. Instead of "return -errno;", use "return negative_errno();"