From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Robbie Harwood <rharwood@redhat.com>
Date: Thu, 9 Mar 2023 11:18:19 -0500
Subject: [PATCH] hostdisk: work around /proc not reporting size

fstat(2) of files in /proc will yield st_size == 0 regardless of file
contents.  Use a negative value in grub_file_t's size to denote "ignore"
and plumb through.

Signed-off-by: Robbie Harwood <rharwood@redhat.com>
---
 grub-core/kern/file.c           | 28 ++++++++++++++++------------
 grub-core/lib/progress.c        |  2 +-
 grub-core/osdep/unix/hostdisk.c |  6 ++++++
 3 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/grub-core/kern/file.c b/grub-core/kern/file.c
index 1794d022fb0..75510df7c92 100644
--- a/grub-core/kern/file.c
+++ b/grub-core/kern/file.c
@@ -172,26 +172,30 @@ grub_file_read (grub_file_t file, void *buf, grub_size_t len)
   grub_disk_read_hook_t read_hook;
   void *read_hook_data;
 
-  if (file->offset > file->size)
-    {
-      grub_error (GRUB_ERR_OUT_OF_RANGE,
-		  N_("attempt to read past the end of file"));
-      return -1;
-    }
-
   if (len == 0)
     return 0;
 
-  if (len > file->size - file->offset)
-    len = file->size - file->offset;
+#ifdef GRUB_MACHINE_EMU
+  if (file->size >= 0)
+    {
+#endif
+      if (file->offset > file->size)
+        {
+          grub_error (GRUB_ERR_OUT_OF_RANGE,
+                      N_("attempt to read past the end of file"));
+          return -1;
+        }
+
+      if (len > file->size - file->offset)
+        len = file->size - file->offset;
+#ifdef GRUB_MACHINE_EMU
+    }
+#endif
 
   /* Prevent an overflow.  */
   if ((grub_ssize_t) len < 0)
     len >>= 1;
 
-  if (len == 0)
-    return 0;
-
   read_hook = file->read_hook;
   read_hook_data = file->read_hook_data;
   if (!file->read_hook)
diff --git a/grub-core/lib/progress.c b/grub-core/lib/progress.c
index 4f4389dd586..eb1b7d13cfd 100644
--- a/grub-core/lib/progress.c
+++ b/grub-core/lib/progress.c
@@ -72,7 +72,7 @@ grub_file_progress_hook_real (grub_disk_addr_t sector __attribute__ ((unused)),
 				       * 100ULL * 1000ULL,
 				       now - file->last_progress_time, 0);
 
-      if (file->size == 0)
+      if (file->size <= 0)
 	percent = 100;
       else
 	percent = grub_divmod64 (100 * file->progress_offset,
diff --git a/grub-core/osdep/unix/hostdisk.c b/grub-core/osdep/unix/hostdisk.c
index 3a00d7451a5..e5f4b4d5f9c 100644
--- a/grub-core/osdep/unix/hostdisk.c
+++ b/grub-core/osdep/unix/hostdisk.c
@@ -71,6 +71,12 @@ grub_util_get_fd_size (grub_util_fd_t fd, const char *name, unsigned *log_secsiz
   if (log_secsize)
     *log_secsize = 9;
 
+#ifdef GRUB_MACHINE_EMU
+  /* /proc doesn't behave itself and gives 0 for file sizes to stat. */
+  if (st.st_size == 0 && !grub_strncmp ("/proc", name, 5))
+    return -1;
+#endif
+
   return st.st_size;
 }