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author | Linus Torvalds <torvalds@linux-foundation.org> | 2012-12-19 07:18:35 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-12-19 07:18:35 -0800 |
commit | 59771079c18c44e39106f0f30054025acafadb41 (patch) | |
tree | 9463781cf1d6f3055bc87840190cc322b59daa67 /Makefile | |
parent | 752451f01c4567b506bf4343082682dbb8fb30dd (diff) | |
download | op-kernel-dev-59771079c18c44e39106f0f30054025acafadb41.zip op-kernel-dev-59771079c18c44e39106f0f30054025acafadb41.tar.gz |
blk: avoid divide-by-zero with zero discard granularity
Commit 8dd2cb7e880d ("block: discard granularity might not be power of
2") changed a couple of 'binary and' operations into modulus operations.
Which turned the harmless case of a zero discard_granularity into a
possible divide-by-zero.
The code also had a much more subtle bug: it was doing the modulus of a
value in bytes using 'sector_t'. That was always conceptually wrong,
but didn't actually matter back when the code assumed a power-of-two
granularity: we only looked at the low bits anyway.
But with potentially arbitrary sector numbers, using a 'sector_t' to
express bytes is very very wrong: depending on configuration it limits
the starting offset of the device to just 32 bits, and any overflow
would result in a wrong value if the modulus wasn't a power-of-two.
So re-write the code to not only protect against the divide-by-zero, but
to do the starting sector arithmetic in sectors, and using the proper
types.
[ For any mathematicians out there: it also looks monumentally stupid to
do the 'modulo granularity' operation *twice*, never mind having a "+
granularity" in the second modulus op.
But that's the easiest way to avoid negative values or overflow, and
it is how the original code was done. ]
Reported-by: Ingo Molnar <mingo@kernel.org>
Reported-by: Doug Anderson <dianders@chromium.org>
Cc: Neil Brown <neilb@suse.de>
Cc: Shaohua Li <shli@fusionio.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Makefile')
0 files changed, 0 insertions, 0 deletions