pipe: iovec: Fix memory corruption when retrying atomic copy as non-a…

…tomic

pipe_iov_copy_{from,to}_user() may be tried twice with the same iovec,
the first time atomically and the second time not.  The second attempt
needs to continue from the iovec position, pipe buffer offset and
remaining length where the first attempt failed, but currently the
pipe buffer offset and remaining length are reset.  This will corrupt
the piped data (possibly also leading to an information leak between
processes) and may also corrupt kernel memory.

This was fixed upstream by commits f0d1bec ("new helper:
copy_page_from_iter()") and 637b58c ("switch pipe_read() to
copy_page_to_iter()"), but those aren't suitable for stable.  This fix
for older kernel versions was made by Seth Jennings for RHEL and I
have extracted it from their update.

CVE-2015-1805

Bug: 27275324

Change-Id: I459adb9076fcd50ff1f1c557089c4e421b036ec4
References: https://bugzilla.redhat.com/show_bug.cgi?id=1202855
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 85c34d007116f8a8aafb173966a605fb03532f45)
(cherry picked from commit f7ebfe91b806501808413c8473a300dff58ddbb5)

fs/pipe.c

@@ -103,51 +103,55 @@ void pipe_wait(struct pipe_inode_info *pipe)
 }
 
 static int
-pipe_iov_copy_from_user(void *to, struct iovec *iov, unsigned long len,
-			int atomic)
+pipe_iov_copy_from_user(void *addr, int *offset, struct iovec *iov,
+			size_t *remaining, int atomic)
 {
 	unsigned long copy;
 
-	while (len > 0) {
+	while (*remaining > 0) {
 		while (!iov->iov_len)
 			iov++;
-		copy = min_t(unsigned long, len, iov->iov_len);
+		copy = min_t(unsigned long, *remaining, iov->iov_len);
 
 		if (atomic) {
-			if (__copy_from_user_inatomic(to, iov->iov_base, copy))
+			if (__copy_from_user_inatomic(addr + *offset,
+						      iov->iov_base, copy))
 				return -EFAULT;
 		} else {
-			if (copy_from_user(to, iov->iov_base, copy))
+			if (copy_from_user(addr + *offset,
+					   iov->iov_base, copy))
 				return -EFAULT;
 		}
-		to += copy;
-		len -= copy;
+		*offset += copy;
+		*remaining -= copy;
 		iov->iov_base += copy;
 		iov->iov_len -= copy;
 	}
 	return 0;
 }
 
 static int
-pipe_iov_copy_to_user(struct iovec *iov, const void *from, unsigned long len,
-		      int atomic)
+pipe_iov_copy_to_user(struct iovec *iov, void *addr, int *offset,
+		      size_t *remaining, int atomic)
 {
 	unsigned long copy;
 
-	while (len > 0) {
+	while (*remaining > 0) {
 		while (!iov->iov_len)
 			iov++;
-		copy = min_t(unsigned long, len, iov->iov_len);
+		copy = min_t(unsigned long, *remaining, iov->iov_len);
 
 		if (atomic) {
-			if (__copy_to_user_inatomic(iov->iov_base, from, copy))
+			if (__copy_to_user_inatomic(iov->iov_base,
+						    addr + *offset, copy))
 				return -EFAULT;
 		} else {
-			if (copy_to_user(iov->iov_base, from, copy))
+			if (copy_to_user(iov->iov_base,
+					 addr + *offset, copy))
 				return -EFAULT;
 		}
-		from += copy;
-		len -= copy;
+		*offset += copy;
+		*remaining -= copy;
 		iov->iov_base += copy;
 		iov->iov_len -= copy;
 	}
@@ -373,7 +377,7 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 			struct pipe_buffer *buf = pipe->bufs + curbuf;
 			const struct pipe_buf_operations *ops = buf->ops;
 			void *addr;
-			size_t chars = buf->len;
+			size_t chars = buf->len, remaining;
 			int error, atomic;
 
 			if (chars > total_len)
@@ -387,9 +391,11 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 			}
 
 			atomic = !iov_fault_in_pages_write(iov, chars);
+			remaining = chars;
 redo:
 			addr = ops->map(pipe, buf, atomic);
-			error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars, atomic);
+			error = pipe_iov_copy_to_user(iov, addr, &buf->offset,
+						      &remaining, atomic);
 			ops->unmap(pipe, buf, addr);
 			if (unlikely(error)) {
 				/*
@@ -404,7 +410,6 @@ pipe_read(struct kiocb *iocb, const struct iovec *_iov,
 				break;
 			}
 			ret += chars;
-			buf->offset += chars;
 			buf->len -= chars;
 			if (!buf->len) {
 				buf->ops = NULL;
@@ -499,6 +504,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 		if (ops->can_merge && offset + chars <= PAGE_SIZE) {
 			int error, atomic = 1;
 			void *addr;
+			size_t remaining = chars;
 
 			error = ops->confirm(pipe, buf);
 			if (error)
@@ -507,8 +513,8 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 			iov_fault_in_pages_read(iov, chars);
 redo1:
 			addr = ops->map(pipe, buf, atomic);
-			error = pipe_iov_copy_from_user(offset + addr, iov,
-							chars, atomic);
+			error = pipe_iov_copy_from_user(addr, &offset, iov,
+							&remaining, atomic);
 			ops->unmap(pipe, buf, addr);
 			ret = error;
 			do_wakeup = 1;
@@ -543,6 +549,8 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 			struct page *page = pipe->tmp_page;
 			char *src;
 			int error, atomic = 1;
+			int offset = 0;
+			size_t remaining;
 
 			if (!page) {
 				page = alloc_page(GFP_HIGHUSER);
@@ -563,14 +571,15 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
 				chars = total_len;
 
 			iov_fault_in_pages_read(iov, chars);
+			remaining = chars;
 redo2:
 			if (atomic)
 				src = kmap_atomic(page, KM_USER0);
 			else
 				src = kmap(page);
 
-			error = pipe_iov_copy_from_user(src, iov, chars,
-							atomic);
+			error = pipe_iov_copy_from_user(src, &offset, iov,
+							&remaining, atomic);
 			if (atomic)
 				kunmap_atomic(src, KM_USER0);
 			else