linux-ext4 - [PATCH 0/5] ext4: Fix softlockups in ext4_seek

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Thu,  3 Mar 2016 11:23:46 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ted Tso <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: [PATCH 0/5] ext4: Fix softlockups in ext4_seek_data()

Hello,

I've seen several reports of softlockups somewhere under ext4_seek_data()
usually during fuzzing. The culprit is that ext4_seek_data() iterates holes
block by block and thus suitably crafted file can make ext4_seek_data() do
a *lot* of lookups using ext4_map_blocks() which is slow. This is really
unnecessary since in principle we have all the information for efficient
skipping of holes, just a layer below. Even for indirect-block based files
we can easily reduce the asymptotic complexity of hole iteration from linear
to logarithmic albeit with a relatively large constant.

Patches 1 and 4 in this series are independent cleanups I've spotted while
changing the code, they can be merged separately. Patches 2 and 3 are
preparatory changes which make ext4_map_blocks() return hole size in
map->m_len field. We still return 0 from ext4_map_blocks() calls finding hole
to maintain backward compatibility of this function and it still makes sense
as such - it still returns the number of allocated blocks starting at given
logical offset. Patch 5 then uses the newly available information in
ext4_seek_data() and it also rewrites ext4_seek_hole() so that both functions
are symmetric.

								Honza
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html