From: Jan Kara <jack@suse.cz>
To: David Turner <novalis@novalis.org>
Cc: Jan Kara <jack@suse.cz>,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
Andreas Dilger <adilger.kernel@dilger.ca>,
"Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH v2] ext4: Fix reading of extended tv_sec (bug 23732)
Date: Fri, 8 Nov 2013 00:14:45 +0100 [thread overview]
Message-ID: <20131107231445.GG2054@quack.suse.cz> (raw)
In-Reply-To: <1383864864.23882.33.camel@chiang>
On Thu 07-11-13 17:54:24, David Turner wrote:
> On Thu, 2013-11-07 at 17:03 +0100, Jan Kara wrote:
> > 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?
>
> This is an error. Here is a corrected version of the patch.
>
>
> --
>
> 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@novalis.org>
> Reported-by: Mark Harris <mh8928@yahoo.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..3c2d0b3 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);
^^^^
Still unnecessary type cast here (but that's a cosmetic issue).
Otherwise the patch looks good. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> + 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;
> }
>
> #define EXT4_INODE_SET_XTIME(xtime, inode, raw_inode) \
> --
> 1.8.1.2
>
>
>
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2013-11-07 23:14 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-07 7:16 [PATCH] ext4: Fix reading of extended tv_sec (bug 23732) David Turner
2013-11-07 16:03 ` Jan Kara
2013-11-07 22:54 ` [PATCH v2] " David Turner
2013-11-07 23:14 ` Jan Kara [this message]
2013-11-07 23:26 ` [PATCH v3] " David Turner
2013-11-08 5:17 ` Theodore Ts'o
2013-11-08 21:37 ` Andreas Dilger
2013-11-09 7:19 ` [PATCH] ext4: explain encoding of 34-bit a,c,mtime values David Turner
2013-11-09 23:51 ` Mark Harris
2013-11-10 7:56 ` David Turner
2013-11-12 0:30 ` Theodore Ts'o
2013-11-12 21:35 ` Andreas Dilger
2013-11-13 7:00 ` [PATCH v4 1/2] ext4: Fix handling of extended tv_sec (bug 23732) David Turner
2013-11-13 8:19 ` Darrick J. Wong
2013-11-13 7:00 ` [PATCH v4 2/2] e2fsck: Correct ext4 dates generated by old kernels David Turner
2013-11-13 7:56 ` Andreas Dilger
2013-11-14 8:38 ` [PATCH v5 1/2] ext4: Fix handling of extended tv_sec (bug 23732) David Turner
2013-11-14 8:44 ` [PATCH v5 2/2] e2fsck: Correct ext4 dates generated by old kernels David Turner
2013-11-14 10:15 ` Mark Harris
2013-11-14 21:06 ` [PATCH v6] " David Turner
2013-11-29 21:54 ` David Turner
2013-11-29 22:11 ` Andreas Dilger
2013-12-07 20:02 ` [PATCH v7 1/2] " David Turner
2013-12-07 22:33 ` Andreas Dilger
2013-12-08 0:53 ` Theodore Ts'o
2013-12-08 2:58 ` David Turner
2013-12-08 3:21 ` Theodore Ts'o
2013-12-07 20:02 ` [PATCH v7 2/2] debugfs: Decode {a,c,cr,m}time_extra fields in stat David Turner
2013-11-12 23:03 ` [PATCH] ext4: explain encoding of 34-bit a,c,mtime values Darrick J. Wong
2013-11-13 2:36 ` David Turner
2014-01-22 6:22 ` Darrick J. Wong
2014-02-11 5:12 ` David Turner
2014-02-11 7:07 ` Andreas Dilger
2014-02-14 3:47 ` [PATCH v8 1/2] ext4: Fix handling of extended tv_sec (bug 23732) David Turner
2014-02-14 3:47 ` [PATCH v8 2/2] e2fsck: Correct ext4 dates generated by old kernels David Turner
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