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Message-ID: <20131107160341.GA3850@quack.suse.cz> Date: Thu, 7 Nov 2013 17:03:41 +0100 From: Jan Kara <jack@...e.cz> To: David Turner <novalis@...alis.org> Cc: linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org, Andreas Dilger <adilger.kernel@...ger.ca>, Theodore Ts'o <tytso@....edu> Subject: Re: [PATCH] ext4: Fix reading of extended tv_sec (bug 23732) On Thu 07-11-13 02:16:30, David Turner wrote: > In ext4, the bottom two bits of {a,c,m}time_extra are used to extend > the {a,c,m}time fields, deferring the year 2038 problem to the year > 2446. The representation (which this patch does not alter) is a bit > hackish, in that the most-significant bit is no longer (alone) > sufficient to indicate the sign. That's because we're representing an > asymmetric range, with seven times as many positive values as > negative. > > When decoding these extended fields, for times whose bottom 32 bits > would represent a negative number, sign extension causes the 64-bit > extended timestamp to be negative as well, which is not what's > intended. This patch corrects that issue, so that the only negative > {a,c,m}times are those between 1901 and 1970 (as per 32-bit signed > timestamps). > > Signed-off-by: David Turner <novalis@...alis.org> > Reported-by: Mark Harris <mh8928@...oo.com> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=23732 > --- > fs/ext4/ext4.h | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > index af815ea..7b73c26 100644 > --- a/fs/ext4/ext4.h > +++ b/fs/ext4/ext4.h > @@ -722,10 +722,15 @@ static inline __le32 ext4_encode_extra_time(struct timespec *time) > > static inline void ext4_decode_extra_time(struct timespec *time, __le32 extra) > { > - if (sizeof(time->tv_sec) > 4) > - time->tv_sec |= (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK) > - << 32; > - time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> EXT4_EPOCH_BITS; > + if (sizeof(time->tv_sec) > 4) { > + u64 extra_bits = (__u64)(le32_to_cpu(extra) & EXT4_EPOCH_MASK); The extra cast to (__u64) looks useless here. > + if (time->tv_sec > 0 || extra_bits != EXT4_EPOCH_MASK) { > + time->tv_sec &= 0xFFFFFFFF; > + time->tv_sec |= extra_bits << 32; > + } > + time->tv_nsec = (le32_to_cpu(extra) & EXT4_NSEC_MASK) >> > + EXT4_EPOCH_BITS; > + } > } So I'm somewhat wondering: Previously we decoded tv_nsec regardless of tv_sec size. After your patch we do it only if sizeof(time->tv_sec) > 4. Is this an intended change? Why is it OK? Honza -- Jan Kara <jack@...e.cz> SUSE Labs, CR -- 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
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