Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sat, 3 Apr 2010 23:41:18 +0300 (EEST) | From | Aaro Koskinen <> | Subject | Re: [PATCH] initramfs: prevent buffer overflow when unpacking to rootfs |
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On Fri, 2 Apr 2010, Andrew Morton wrote: > On Thu, 1 Apr 2010 12:45:46 +0300 > Aaro Koskinen <aaro.koskinen@iki.fi> wrote: > >> Garbage in the initrd memory area may result in the unpack routine >> accessing memory outside the buffer. The patch adds a check that the >> specified area size is not exceeded. >> >> Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi> >> Cc: stable <stable@kernel.org> >> --- >> >> The patch prevents the following kernel panic on Amstrad E3: >> >> Unpacking initramfs... >> Unable to handle kernel paging request at virtual address c20121a7 >> >> ... >> >> --- a/init/initramfs.c >> +++ b/init/initramfs.c >> @@ -460,6 +460,8 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len) >> } >> if (state != Reset) >> error("junk in compressed archive"); >> + if (my_inptr >= len) >> + break; >> this_header = saved_offset + my_inptr; >> buf += my_inptr; >> len -= my_inptr; > > OK, so if I'm understanding this right, the call to > > decompress(buf, len, NULL, flush_buffer, NULL, &my_inptr, error); > > has gone and generated more output data than it was asked to generate? > > If so, isn't that a bug in the decompressor? Which one is your system using?
The decompressor is gzip, and it returned correct buffer position.
The problem was that the loop in unpack_to_rootfs() continued to process the remaining buffer. my_inptr was never again updated (decompress_method() did not recognize the remaining garbage data, so there was no further calls to decompressor). The loop kept subtracting my_inptr from len eventually exceeding it. Perhaps there should be some better logic to give up earlier.
A.
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