master 579eefda36: Don't follow symlinks in w32notify file watches

[Eli Zaretskii]

branch: master
commit 579eefda36b9a8cd71c9aeff0f32e32d468727a3
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Don't follow symlinks in w32notify file watches
    
    * src/w32notify.c (add_watch): On filesystems that support
    symlinks, don't follow symlinks.  (Bug#57536)
    * src/w32.c (symlinks_supported): New function.
    * src/w32.h (symlinks_supported): Add prototype.
---
 src/w32.c       | 11 +++++++++++
 src/w32.h       |  2 ++
 src/w32notify.c | 12 ++++++++----
 3 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/w32.c b/src/w32.c
index 44c279602c..9c7d536ada 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -6480,6 +6480,17 @@ chase_symlinks (const char *file)
   return target;
 }
 
+/* Return non-zero if FILE's filesystem supports symlinks.  */
+bool
+symlinks_supported (const char *file)
+{
+  if (is_windows_9x () != TRUE
+      && get_volume_info (file, NULL)
+      && (volume_info.flags & FILE_SUPPORTS_REPARSE_POINTS) != 0)
+    return true;
+  return false;
+}
+
 
 /* Posix ACL emulation.  */
 
diff --git a/src/w32.h b/src/w32.h
index dc91c595c4..b914aa9baf 100644
--- a/src/w32.h
+++ b/src/w32.h
@@ -228,6 +228,8 @@ extern int sys_link (const char *, const char *);
 extern int openat (int, const char *, int, int);
 extern int fchmodat (int, char const *, mode_t, int);
 extern int lchmod (char const *, mode_t);
+extern bool symlinks_supported (const char *);
+
 
 /* Return total and free memory info.  */
 extern int w32_memory_info (unsigned long long *, unsigned long long *,
diff --git a/src/w32notify.c b/src/w32notify.c
index 72e634f77c..6b5fce9f92 100644
--- a/src/w32notify.c
+++ b/src/w32notify.c
@@ -367,6 +367,12 @@ add_watch (const char *parent_dir, const char *file, BOOL 
subdirs, DWORD flags)
   if (!file)
     return NULL;
 
+  /* Do not follow symlinks, so that the caller could watch symlink
+     files.  */
+  DWORD crflags = FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED;
+  if (symlinks_supported (parent_dir))
+    crflags |= FILE_FLAG_OPEN_REPARSE_POINT;
+
   if (w32_unicode_filenames)
     {
       wchar_t dir_w[MAX_PATH], file_w[MAX_PATH];
@@ -383,8 +389,7 @@ add_watch (const char *parent_dir, const char *file, BOOL 
subdirs, DWORD flags)
                             processes from deleting files inside
                             parent_dir.  */
                          FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
-                         NULL, OPEN_EXISTING,
-                         FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
+                         NULL, OPEN_EXISTING, crflags,
                          NULL);
     }
   else
@@ -400,8 +405,7 @@ add_watch (const char *parent_dir, const char *file, BOOL 
subdirs, DWORD flags)
       hdir = CreateFileA (dir_a,
                          FILE_LIST_DIRECTORY,
                          FILE_SHARE_READ|FILE_SHARE_WRITE|FILE_SHARE_DELETE,
-                         NULL, OPEN_EXISTING,
-                         FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OVERLAPPED,
+                         NULL, OPEN_EXISTING, crflags,
                          NULL);
     }
   if (hdir == INVALID_HANDLE_VALUE)