e2fsck: make sure get_backup_sb() works when ctx is NULL

The print_e2fsck_message() function can call get_backup_sb() with the
ctx variable set to NULL.  In that case, we can't dereference
ctx->filesystem_name; instead, we can get the size of the file system
from the ext2fs_block_count(fs->super).

Addresses-Coverity-Bug: 1596517
Addresses-Coverity-Bug: 1596505
Fixes: b53ce7848c2e ("e2fsck: don't try backup superblocks beyond...")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/e2fsck/util.c b/e2fsck/util.c
index 734e45c..b8deb41 100644 (file)
--- a/e2fsck/util.c
+++ b/e2fsck/util.c
@@ -592,9 +592,11 @@ blk64_t get_backup_sb(e2fsck_t ctx, ext2_filsys fs, const char *name,
                blk_t this_bpg = bpg ? bpg : blocksize * 8;
                blk64_t num_blocks;
 
-               if (ext2fs_get_device_size2(ctx->filesystem_name,
-                                           blocksize,
-                                           &num_blocks) == 0) {
+               if (fs && fs->super) {
+                       num_blocks = ext2fs_blocks_count(fs->super);
+               } else if (ctx && ext2fs_get_device_size2(ctx->filesystem_name,
+                                                         blocksize,
+                                                         &num_blocks) == 0) {
                        limit = num_blocks / this_bpg;
                } else {
                        /* If we can't figure out the device size,