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[PATCH 1/2] fs/pipe.c: preserve alloc_file() error code

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  [PATCH 1/2] fs/pipe.c: preserve alloc_file() error code Eric Biggers <ebiggers3@gmail.com> - 2015-10-17 23:30 +0200
    [PATCH 2/2] fs/pipe.c: return error code rather than 0 in pipe_write() Eric Biggers <ebiggers3@gmail.com> - 2015-10-17 23:30 +0200

#1249468 — [PATCH 1/2] fs/pipe.c: preserve alloc_file() error code

If sys_pipe() was unable to allocate a 'struct file', it always failed
with ENFILE, which means "The number of simultaneously open files in the
system would exceed a system-imposed limit." However, alloc_file()
actually returns an ERR_PTR value and might fail with other error codes.
Currently, in addition to ENFILE, it can fail with ENOMEM, potentially
when there are few open files in the system.  Update sys_pipe() to
preserve this error code.

In a prior submission of a similar patch (1) some concern was raised
about introducing a new error code for sys_pipe().  However, for most
system calls, programs cannot assume that new error codes will never be
introduced.  In addition, ENOMEM was, in fact, already a possible error
code for sys_pipe(), in the case where the file descriptor table could
not be expanded due to insufficient memory.

	(1) http://comments.gmane.org/gmane.linux.kernel/1357942

Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
---
 fs/pipe.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 8865f79..997de34 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -693,17 +693,20 @@ int create_pipe_files(struct file **res, int flags)
 
 	d_instantiate(path.dentry, inode);
 
-	err = -ENFILE;
 	f = alloc_file(&path, FMODE_WRITE, &pipefifo_fops);
-	if (IS_ERR(f))
+	if (IS_ERR(f)) {
+		err = PTR_ERR(f);
 		goto err_dentry;
+	}
 
 	f->f_flags = O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT));
 	f->private_data = inode->i_pipe;
 
 	res[0] = alloc_file(&path, FMODE_READ, &pipefifo_fops);
-	if (IS_ERR(res[0]))
+	if (IS_ERR(res[0])) {
+		err = PTR_ERR(res[0]);
 		goto err_file;
+	}
 
 	path_get(&path);
 	res[0]->private_data = inode->i_pipe;
-- 
2.6.1

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#1249470 — [PATCH 2/2] fs/pipe.c: return error code rather than 0 in pipe_write()

pipe_write() would return 0 if it failed to merge the beginning of the
data to write with the last, partially filled pipe buffer.  It should
return an error code instead.  Userspace programs could be confused by
write() returning 0 when called with a nonzero 'count'.

The EFAULT error case was a regression from f0d1bec9d5 ("new helper:
copy_page_from_iter()"), while the ops->confirm() error case was a much
older bug.

Test program:

	#include <assert.h>
	#include <errno.h>
	#include <unistd.h>

	int main(void)
	{
		int fd[2];
		char data[1] = {0};

		assert(0 == pipe(fd));
		assert(1 == write(fd[1], data, 1));

		/* prior to this patch, write() returned 0 here  */
		assert(-1 == write(fd[1], NULL, 1));
		assert(errno == EFAULT);
	}

Signed-off-by: Eric Biggers <ebiggers3@gmail.com>
---
 fs/pipe.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 997de34..42cf8dd 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -366,18 +366,17 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 		int offset = buf->offset + buf->len;
 
 		if (ops->can_merge && offset + chars <= PAGE_SIZE) {
-			int error = ops->confirm(pipe, buf);
-			if (error)
+			ret = ops->confirm(pipe, buf);
+			if (ret)
 				goto out;
 
 			ret = copy_page_from_iter(buf->page, offset, chars, from);
 			if (unlikely(ret < chars)) {
-				error = -EFAULT;
+				ret = -EFAULT;
 				goto out;
 			}
 			do_wakeup = 1;
-			buf->len += chars;
-			ret = chars;
+			buf->len += ret;
 			if (!iov_iter_count(from))
 				goto out;
 		}
-- 
2.6.1

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