Fix QStorageInfo inability to parse really long mountinfo lines

Docker creates really long lines due to the multiple levels of overlays
in the overlayfs. Our limit of 1024 bytes was too short.

[ChangeLog][QtCore][QStorageInfo] Fixed a bug that caused QStorageInfo
to be unable to report all filesystems if the options to mounted
filesystems were too long (over 900 characters, roughly), such as those
found in Docker overlay mounts.

Fixes: QTBUG-77059
Change-Id: I6aed4df6a12e43c3ac8efffd15b1ba4231e60b4a
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 12 insertions, 2 deletions

diff --git a/src/corelib/io/qstorageinfo_unix.cpp b/src/corelib/io/qstorageinfo_unix.cpp
index 11b5af069a..812e965927 100644
--- a/src/corelib/io/qstorageinfo_unix.cpp
+++ b/src/corelib/io/qstorageinfo_unix.cpp
@@ -468,8 +468,18 @@ inline bool QStorageIterator::next()
     size_t len = strlen(buffer.data());
     if (len == 0)
         return false;
-    if (ptr[len - 1] == '\n')
-        ptr[len - 1] = '\0';
+    while (Q_UNLIKELY(ptr[len - 1] != '\n' && !feof(fp))) {
+        // buffer wasn't large enough. Enlarge and try again.
+        // (we're readidng from the kernel, so OOM is unlikely)
+        buffer.resize((buffer.size() + 4096) & ~4095);
+        ptr = buffer.data();
+        if (fgets(ptr + len, buffer.size() - len, fp) == nullptr)
+            return false;
+
+        len += strlen(ptr + len);
+        Q_ASSERT(len < size_t(buffer.size()));
+    }
+    ptr[len - 1] = '\0';
 
     // parse the line
     bool ok;