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Re: [Qemu-stable] [PATCH 1/2] block/file-posix: Fix fully preallocated t
From: |
Max Reitz |
Subject: |
Re: [Qemu-stable] [PATCH 1/2] block/file-posix: Fix fully preallocated truncate |
Date: |
Wed, 28 Feb 2018 14:45:49 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 |
On 2018-02-28 14:34, Daniel P. Berrangé wrote:
> On Wed, Feb 28, 2018 at 02:13:14PM +0100, Max Reitz wrote:
>> Storing the lseek() result in an int results in it overflowing when the
>> file is at least 2 GB big. Then, we have a 50 % chance of the result
>> being "negative" and thus thinking an error occurred when actually
>> everything went just fine.
>>
>> So we should use the correct type for storing the result: off_t.
>>
>> Reported-by: Daniel P. Berrange <address@hidden>
>> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1549231
>> Cc: address@hidden
>> Signed-off-by: Max Reitz <address@hidden>
>> ---
>> block/file-posix.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/file-posix.c b/block/file-posix.c
>> index f1591c3849..90c25864a0 100644
>> --- a/block/file-posix.c
>> +++ b/block/file-posix.c
>> @@ -1697,6 +1697,7 @@ static int raw_regular_truncate(int fd, int64_t
>> offset, PreallocMode prealloc,
>> case PREALLOC_MODE_FULL:
>> {
>> int64_t num = 0, left = offset - current_length;
>> + off_t seek_result;
>>
>> /*
>> * Knowing the final size from the beginning could allow the file
>> @@ -1711,8 +1712,8 @@ static int raw_regular_truncate(int fd, int64_t
>> offset, PreallocMode prealloc,
>>
>> buf = g_malloc0(65536);
>>
>> - result = lseek(fd, current_length, SEEK_SET);
>> - if (result < 0) {
>> + seek_result = lseek(fd, current_length, SEEK_SET);
>> + if (seek_result < 0) {
>
> off_t is an unsigned type, so this comparison to "< 0" is bogus - only the
> exact value (off_t)-1 indicates an error. So this needs to be
>
> if (seek_result == (off_t)-1) {
> ...
> }
Hmmm... On my system, it appears to be a long int[1]. And
find_allocation() does an off_t < 0 comparison already. And
"man 0p sys_types.h" says "blkcnt_t and off_t shall be signed integer
types."
Max
[1]
#define do_stringify(x) #x
#define stringify(x) do_stringify(x)
int main(void)
{
printf("%s\n", stringify(__OFF_T_TYPE));
}
Output: long int
signature.asc
Description: OpenPGP digital signature
Re: [Qemu-stable] [PATCH 1/2] block/file-posix: Fix fully preallocated truncate, Daniel P . Berrangé, 2018/02/28
Re: [Qemu-stable] [Qemu-devel] [PATCH 0/2] block/file-posix: Fix fully preallocated truncate, Eric Blake, 2018/02/28