2011/6/23 Akira Fujita <a-fujita@xxxxxxxxxxxxx>: >> https://bugzilla.kernel.org/show_bug.cgi?id=23732 > > ext4: Fix ext4 timestamps corruption > > Officially, ext4 can handle its timestamps until 2514 > with 32bit entries plus EPOCH_BIT (2bits). > But when timestamps values use 32+ bit > (e.g. 2038-01-19 9:14:08 0x0000000080000000), > we can get corrupted values. > Because sign bit is overwritten by transferring value > between kernel space and user space. > > To fix this issue, 32th bit of extra time fields in ext4_inode structure > (e.g. i_ctime_extra) are used as the sign for 64bit user space. > Because these are used only 20bits for nano-second and bottom of 2bits > are for EXT4_EPOCH_BITS shift. > With this patch, ext4 supports timestamps Y1901-2514. Thanks for looking into this bug. However tv_nsec is in the range 0..999999999 and requires 30 bits. That is why tv_sec was only extended by 2 bits. So there are no additional spare bits in the "extra" field. 34-bit seconds can accommodate a maximum of 544.4 years, e.g. 1970..2514 or 1901..2446. Although an early version of the patch for 34-bit tv_sec in ext4 worked with years 1970..2514, prior to being committed the patch was changed to support pre-1970 timestamps (introducing the sign extension issue in the decoding): http://marc.info/?l=linux-ext4&m=118208541320999 The existing encoding simply encodes bits 31..0 of tv_sec in the regular time field and bits 33..32 in the extra field (along with the 30-bit tv_nsec). The issue is in the decoding, which I think can be addressed by changing only the body of the "if" in in the ext4_decode_extra_time function, to something like this: time->tv_sec += ((__u32)time->tv_sec + ((__u64)le32_to_cpu(extra) << 32) + 0x80000000LL) & 0x300000000LL; This is untested, and might look nicer with some macros, but it should decode the 34 bits into a timestamp in the range -0x80000000 (1901-12-13) to 0x37fffffff (2446-05-10), while retaining compatibility with the existing encoding. 2 msb of adjustment needed to convert extra 32-bit sign-extended 32-bit tv_sec bits time decoded 64-bit tv_sec to decoded 64-bit tv_sec 1 1 1 -0x80000000..-1 0 0 0 0 0x000000000..0x07fffffff 0 0 0 1 0x080000000..0x0ffffffff 0x100000000 0 1 0 0x100000000..0x17fffffff 0x100000000 0 1 1 0x180000000..0x1ffffffff 0x200000000 1 0 0 0x200000000..0x27fffffff 0x200000000 1 0 1 0x280000000..0x2ffffffff 0x300000000 1 1 0 0x300000000..0x37fffffff 0x300000000 - Mark -- 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
