Legacy ImageMagick Discussions Archive

This code in magick/blob.c can legally return any count as a result:

2789     case StandardStream:
2790     {
2791       count=read(fileno(image->blob->file_info.file),q,length);
2792       break;
2793     }

According to manual:

It is not an error if this number is smaller than the number of bytes requested

This command line performs on GNU/Linux successfully for lower N, always fails for higher N and behaves randomly on N between 50 and 200, depending on system speed. See two convert calls that work with same data, but gain different results:

Code: Select all

$ export N=150; head -c $(($N*$N*3)) /dev/urandom | tee img | convert -depth 8 -size ${N}x${N} rgb:- o.raw
convert: unexpected end-of-file `-': No such file or directory @ error/rgb.c/ReadRGBImage/231.
$ cat img | convert -depth 8 -size ${N}x${N} rgb:- o.raw
$ ls -l o.raw
-rw-r--r-- 1 george george 67500 Apr 25 15:43 o.raw

Actually this can happen independent of I/O type, only it must be slow enough. I see no solution but using fread() here.

We can't use fread because its buffered and that causes other sorts of problems, but we can put the read in a loop until the read completes. We'll get a patch in ImageMagick 6.8.5-1 Beta within a few days.

magick wrote:we can put the read in a loop until the read completes

Read loop, yes. By the way, I've reverted that very part of code, but got the same error even on file I/O (on heavy loaded system). Probably, more thorough read() check is needed.

UPD Alert clear, that was my fault. Read loop seems to be enough.

Legacy ImageMagick Discussions Archive

Dangerous usage of read() in ReadBlob()

Dangerous usage of read() in ReadBlob()

Re: Dangerous usage of read() in ReadBlob()

Re: Dangerous usage of read() in ReadBlob()