Re: [PATCH 2.6.32-3.14] pipe: Fix buffer offset after partially failed read

[Jiri Slaby <jslaby@suse.cz>]

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On 02/13/2016, 07:42 PM, Ben Hutchings wrote:
> Quoting the RHEL advisory:
> 
>> It was found that the fix for CVE-2015-1805 incorrectly kept
>> buffer offset and buffer length in sync on a failed atomic read,
>> potentially resulting in a pipe buffer state corruption. A local,
>> unprivileged user could use this flaw to crash the system or leak
>> kernel memory to user space. (CVE-2016-0774, Moderate)
> 
> The same flawed fix was applied to stable branches from 2.6.32.y
> to 3.14.y inclusive, and I was able to reproduce the issue on
> 3.2.y. We need to give pipe_iov_copy_to_user() a separate offset
> variable and only update the buffer offset if it succeeds.
> 
> References: https://rhn.redhat.com/errata/RHSA-2016-0103.html 
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

Thanks, now applied to 3.12.

> --- a/fs/pipe.c +++ b/fs/pipe.c @@ -395,6 +395,7 @@
> pipe_read(struct kiocb *iocb, const stru void *addr; size_t chars =
> buf->len, remaining; int error, atomic; +			int offset;
> 
> if (chars > total_len) chars = total_len; @@ -408,9 +409,10 @@
> pipe_read(struct kiocb *iocb, const stru
> 
> atomic = !iov_fault_in_pages_write(iov, chars); remaining = chars; 
> +			offset = buf->offset; redo: addr = ops->map(pipe, buf,
> atomic); -			error = pipe_iov_copy_to_user(iov, addr,
> &buf->offset, +			error = pipe_iov_copy_to_user(iov, addr,
> &offset, &remaining, atomic); ops->unmap(pipe, buf, addr); if
> (unlikely(error)) { @@ -426,6 +428,7 @@ redo: break; } ret +=
> chars; +			buf->offset += chars; buf->len -= chars;
> 
> /* Was it a packet buffer? Clean up and exit */
> 


- -- 
js
suse labs
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