From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49674) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1er1sh-0000uR-GW for qemu-devel@nongnu.org; Wed, 28 Feb 2018 08:34:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1er1sg-00027k-I5 for qemu-devel@nongnu.org; Wed, 28 Feb 2018 08:34:51 -0500 Date: Wed, 28 Feb 2018 13:34:34 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180228133434.GL17774@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20180228131315.30194-1-mreitz@redhat.com> <20180228131315.30194-2-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180228131315.30194-2-mreitz@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/2] block/file-posix: Fix fully preallocated truncate List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Kevin Wolf , qemu-stable@nongnu.org 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 > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1549231 > Cc: qemu-stable@nongnu.org > Signed-off-by: Max Reitz > --- > 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) { ... } Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|