libblkid: fix buffer usage in FAT prober

The blkid_probe_get_buffer() function returns buffer that could be
overwritten in the next blkid_probe_get_buffer() call. It means that
we have to save FAT super block to the temporary buffer if we want to
call blkid_probe_get_buffer() for directory entries or fsinfo.

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/shlibs/blkid/src/superblocks/vfat.c b/shlibs/blkid/src/superblocks/vfat.c
index 8343c65c8e9dd647343cddc7ee21a791d4abe0bc..c47addbe74ff338aecf3cd075f566913340602cc 100644 (file)
--- a/shlibs/blkid/src/superblocks/vfat.c
+++ b/shlibs/blkid/src/superblocks/vfat.c
@@ -189,14 +189,14 @@ static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
        struct vfat_super_block *vs;
        struct msdos_super_block *ms;
        struct vfat_dir_entry *dir;
-       const unsigned char *vol_label = 0, *tmp;
+       const unsigned char *vol_label = NULL, *tmp;
        unsigned char   *vol_serno;
        int maxloop = 100;
        uint16_t sector_size, dir_entries, reserved;
        uint32_t sect_count, fat_size, dir_size, cluster_count, fat_length;
        uint32_t buf_size, start_data_sect, next, root_start, root_dir_entries;
        const char *version = NULL;
-
+       unsigned char sb_buf[512], label_buf[11];
 
        /* non-standard magic strings */
        if (mag->len <= 2 && probe_fat_nomagic(pr, mag) != 0)
@@ -241,6 +241,12 @@ static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
        if (cluster_count > FAT32_MAX)
                return 1;
 
+       /* all basic checks pass -- save the superblock to avoid overwriting
+        * by the next blkid_probe_get_buffer() call */
+       memcpy(sb_buf, vs, sizeof(sb_buf));
+       ms = (struct msdos_super_block *) sb_buf;
+       vs = (struct vfat_super_block *) sb_buf;
+
        if (ms->ms_fat_length) {
                /* the label may be an attribute in the root directory */
                root_start = (reserved + fat_size) * sector_size;
@@ -268,6 +274,7 @@ static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
                unsigned char *buf;
                uint16_t fsinfo_sect;
 
+
                /* Search the FAT32 root dir for the label attribute */
                buf_size = vs->vs_cluster_size * sector_size;
                start_data_sect = reserved + fat_size;
@@ -292,8 +299,12 @@ static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
                        count = buf_size / sizeof(struct vfat_dir_entry);
 
                        vol_label = search_fat_label(dir, count);
-                       if (vol_label)
+                       if (vol_label) {
+                               /* save the root dir entry label */
+                               memcpy(label_buf, vol_label, sizeof(label_buf));
+                               vol_label = label_buf;
                                break;
+                       }
 
                        /* get FAT entry */
                        fat_entry_off = (reserved * sector_size) +