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| author | Ben Hutchings <ben@decadent.org.uk> | 2016-02-13 18:42:26 +0000 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2016-03-12 14:25:41 +0100 |
| commit | 42646fbfdee0717b3d4c164e15d31b608d6ece97 (patch) | |
| tree | 343181af38b2d7e6a4bee5addcfd0d8b84ae5ecc | |
| parent | adfdad98d876fc9e43746522d6329d482edca6b3 (diff) | |
| download | lwn-42646fbfdee0717b3d4c164e15d31b608d6ece97.tar.gz lwn-42646fbfdee0717b3d4c164e15d31b608d6ece97.zip | |
pipe: Fix buffer offset after partially failed read
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>
| -rw-r--r-- | fs/pipe.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/fs/pipe.c b/fs/pipe.c index daa71ea5eb81..d34cce99ac72 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -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 @@ redo: break; } ret += chars; + buf->offset += chars; buf->len -= chars; if (!buf->len) { buf->ops = NULL; |