On Tue, Mar 29, 2011 at 08:50:18AM -0500, Eric Sandeen wrote: > Another tool which can be useful for this sort of thing is > fsfuzzer. It writes garbage; using dd to write zeros actually > might be "nice" corruption. Besides writing blocks of "random data", you could write blocks with a small percentage of bits (byte) set to non-zero, or just toggle a configurable number of bits (bytes). This is slightly more devious than just "random data". If you try to verify the integrity of a block full of random data, you can quickly determine that it is completely bogus (I don't think that e2fsck already exploits this as I've seen it get this wrong). If you have an indirect block, and it contains: 00000 72 6f 6f 74 3a 78 3a 30 3a 30 3a 72 6f 6f 74 3a root:x:0:0:root: 00010 2f 72 6f 6f 74 3a 2f 62 69 6e 2f 62 61 73 68 0a /root:/bin/bash. 00020 64 61 65 6d 6f 6e 3a 78 3a 31 3a 31 3a 64 61 65 daemon:x:1:1:dae 00030 6d 6f 6e 3a 2f 75 73 72 2f 73 62 69 6e 3a 2f 62 mon:/usr/sbin:/b 00040 69 6e 2f 73 68 0a 62 69 6e 3a 78 3a 32 3a 32 3a in/sh.bin:x:2:2: 00050 62 69 6e 3a 2f 62 69 6e 3a 2f 62 69 6e 2f 73 68 bin:/bin:/bin/sh 00060 0a 73 79 73 3a 78 3a 33 3a 33 3a 73 79 73 3a 2f .sys:x:3:3:sys:/ 00070 64 65 76 3a 2f 62 69 6e 2f 73 68 0a 73 79 6e 63 dev:/bin/sh.sync 00080 3a 78 3a 34 3a 36 35 35 33 34 3a 73 79 6e 63 3a :x:4:65534:sync: 00090 2f 62 69 6e 3a 2f 62 69 6e 2f 73 79 6e 63 0a 67 /bin:/bin/sync.g You can see that the block numbers that are represented here are all bad. In this case, one of the options should be to discard the whole indirect block. If you happen to find a few "valid" block numbers here, they are likely to be bogus. It is counterproductive to check those for duplicate allocation, or to mark them as used if they happen to be free. Roger. -- ** R.E.Wolff@xxxxxxxxxxxx ** http://www.BitWizard.nl/ ** +31-15-2600998 ** ** Delftechpark 26 2628 XH Delft, The Netherlands. KVK: 27239233 ** *-- BitWizard writes Linux device drivers for any device you may have! --* Q: It doesn't work. A: Look buddy, doesn't work is an ambiguous statement. Does it sit on the couch all day? Is it unemployed? Please be specific! Define 'it' and what it isn't doing. --------- Adapted from lxrbot FAQ -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
