[Qemu-devel] [PATCH 11/13] vvfat: limit number of entries in root directory in FAT12/FAT16

[Hervé Poussineau]

FAT12/FAT16 root directory is two sectors in size, which allows only 512 
directory entries.
Prevent QEMU startup if too much files exist, instead of overflowing root 
directory.

Also introduce variable root_entries, which will be required if we support 
loading
a custom bootsector (bootsect.img).

Fixes: https://bugs.launchpad.net/qemu/+bug/1599539/comments/4
Signed-off-by: Hervé Poussineau <address@hidden>
---
 block/vvfat.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/block/vvfat.c b/block/vvfat.c
index 98978df404..7b21d6bb21 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -331,8 +331,9 @@ typedef struct BDRVVVFATState {
     unsigned int cluster_size;
     unsigned int sectors_per_cluster;
     unsigned int sectors_per_fat;
-    unsigned int sectors_of_root_directory;
     uint32_t last_cluster_of_root_directory;
+    /* how many entries are available in root directory (0 for FAT32) */
+    uint16_t root_entries;
     uint32_t sector_count; /* total number of sectors of the partition */
     uint32_t cluster_count; /* total number of clusters of this partition */
     uint32_t max_fat_value;
@@ -846,6 +847,12 @@ static int read_directory(BDRVVVFATState* s, int 
mapping_index)
         int is_dot=!strcmp(entry->d_name,".");
         int is_dotdot=!strcmp(entry->d_name,"..");
 
+        if (first_cluster == 0 && s->directory.next >= s->root_entries - 1) {
+            fprintf(stderr, "Too many entries in root directory\n");
+            closedir(dir);
+            return -2;
+        }
+
         if(first_cluster == 0 && (is_dotdot || is_dot))
             continue;
 
@@ -919,15 +926,15 @@ static int read_directory(BDRVVVFATState* s, int 
mapping_index)
         memset(direntry,0,sizeof(direntry_t));
     }
 
-/* TODO: if there are more entries, bootsector has to be adjusted! */
-#define ROOT_ENTRIES (0x02 * 0x10 * s->sectors_per_cluster)
-    if (mapping_index == 0 && s->directory.next < ROOT_ENTRIES) {
+    if (s->fat_type != 32 &&
+        mapping_index == 0 &&
+        s->directory.next < s->root_entries) {
         /* root directory */
         int cur = s->directory.next;
-        array_ensure_allocated(&(s->directory), ROOT_ENTRIES - 1);
-        s->directory.next = ROOT_ENTRIES;
+        array_ensure_allocated(&(s->directory), s->root_entries - 1);
+        s->directory.next = s->root_entries;
         memset(array_get(&(s->directory), cur), 0,
-                (ROOT_ENTRIES - cur) * sizeof(direntry_t));
+                (s->root_entries - cur) * sizeof(direntry_t));
     }
 
     /* reset the mapping, since s->mapping was possibly realloc()ed */
@@ -992,6 +999,8 @@ static int init_directories(BDRVVVFATState* s,
     /* Now build FAT, and write back information into directory */
     init_fat(s);
 
+    /* TODO: if there are more entries, bootsector has to be adjusted! */
+    s->root_entries = 0x02 * 0x10 * s->sectors_per_cluster;
     s->cluster_count=sector2cluster(s, s->sector_count);
 
     mapping = array_get_next(&(s->mapping));
@@ -1060,7 +1069,6 @@ static int init_directories(BDRVVVFATState* s,
     }
 
     mapping = array_get(&(s->mapping), 0);
-    s->sectors_of_root_directory = mapping->end * s->sectors_per_cluster;
     s->last_cluster_of_root_directory = mapping->end;
 
     /* the FAT signature */
@@ -1079,7 +1087,7 @@ static int init_directories(BDRVVVFATState* s,
     bootsector->sectors_per_cluster=s->sectors_per_cluster;
     bootsector->reserved_sectors=cpu_to_le16(1);
     bootsector->number_of_fats=0x2; /* number of FATs */
-    bootsector->root_entries=cpu_to_le16(s->sectors_of_root_directory*0x10);
+    bootsector->root_entries = cpu_to_le16(s->root_entries);
     
bootsector->total_sectors16=s->sector_count>0xffff?0:cpu_to_le16(s->sector_count);
     bootsector->media_type = (s->offset_to_bootsector > 0 ? 0xf8 : 0xf0);
     s->fat.pointer[0] = bootsector->media_type;
-- 
2.11.0