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Date: Mon, 18 Apr 2016 18:46:35 +0800 From: lizf@...nel.org To: stable@...r.kernel.org Cc: linux-kernel@...r.kernel.org, Ben Hutchings <ben@...adent.org.uk>, Jeffrey Vander Stoep <jeffv@...gle.com>, Zefan Li <lizefan@...wei.com> Subject: [PATCH 3.4 90/92] pipe: Fix buffer offset after partially failed read From: Ben Hutchings <ben@...adent.org.uk> 3.4.112-rc1 review patch. If anyone has any objections, please let me know. ------------------ 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@...adent.org.uk> Cc: Jeffrey Vander Stoep <jeffv@...gle.com> Signed-off-by: Zefan Li <lizefan@...wei.com> --- fs/pipe.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/pipe.c b/fs/pipe.c index abfb935..6049235 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -390,6 +390,7 @@ 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; @@ -403,9 +404,10 @@ 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)) { @@ -421,6 +423,7 @@ redo: break; } ret += chars; + buf->offset += chars; buf->len -= chars; /* Was it a packet buffer? Clean up and exit */ -- 1.9.1
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