e2fsck: fix potential Floating Point Exception in show_stats()

If the free inodes count in the superblock is equal to the inodes
count in the superblock (which is not possible with a valid file
system and will be fixed by e2fsck unless it is prevented by, for
example, e2fsck -n), it is possible for e2fsck to crash due to a
divide by zero error.

Fix this potential bug.

Addresses-Debian-Bug: #879220

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/e2fsck/unix.c b/e2fsck/unix.c
index b46dcb2..2e9be8b 100644 (file)
--- a/e2fsck/unix.c
+++ b/e2fsck/unix.c
@@ -106,7 +106,7 @@ static void show_stats(e2fsck_t     ctx)
        unsigned int dir_links;
        unsigned int num_files, num_links;
        __u32 *mask, m;
-       int frag_percent_file, frag_percent_dir, frag_percent_total;
+       int frag_percent_file = 0, frag_percent_dir = 0, frag_percent_total = 0;
        int i, j, printed = 0;
 
        dir_links = 2 * ctx->fs_directory_count - 1;
@@ -119,16 +119,18 @@ static void show_stats(e2fsck_t   ctx)
        blocks_used = (ext2fs_blocks_count(fs->super) -
                       ext2fs_free_blocks_count(fs->super));
 
-       frag_percent_file = (10000 * ctx->fs_fragmented) / inodes_used;
-       frag_percent_file = (frag_percent_file + 5) / 10;
+       if (inodes_used > 0) {
+               frag_percent_file = (10000 * ctx->fs_fragmented) / inodes_used;
+               frag_percent_file = (frag_percent_file + 5) / 10;
 
-       frag_percent_dir = (10000 * ctx->fs_fragmented_dir) / inodes_used;
-       frag_percent_dir = (frag_percent_dir + 5) / 10;
+               frag_percent_dir = (10000 * ctx->fs_fragmented_dir) / inodes_used;
+               frag_percent_dir = (frag_percent_dir + 5) / 10;
 
-       frag_percent_total = ((10000 * (ctx->fs_fragmented +
-                                       ctx->fs_fragmented_dir))
-                             / inodes_used);
-       frag_percent_total = (frag_percent_total + 5) / 10;
+               frag_percent_total = ((10000 * (ctx->fs_fragmented +
+                                               ctx->fs_fragmented_dir))
+                                     / inodes_used);
+               frag_percent_total = (frag_percent_total + 5) / 10;
+       }
 
        if (!verbose) {
                log_out(ctx, _("%s: %u/%u files (%0d.%d%% non-contiguous), "