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pipe: Fix buffer offset after partially failed read

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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>
Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Ben Hutchings 2016-02-13 18:42:26 +00:00 committed by Willy Tarreau
parent adfdad98d8
commit 42646fbfde
1 changed files with 4 additions and 1 deletions
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5
fs/pipe.c
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@ -360,6 +360,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
void *addr;
size_t chars = buf->len, remaining;
int error, atomic;
int offset;
if (chars > total_len)
chars = total_len;
@ -373,9 +374,10 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
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)) {
@ -391,6 +393,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
break;
}
ret += chars;
buf->offset += chars;
buf->len -= chars;
if (!buf->len) {
buf->ops = NULL;