[PATCH 4.1 63/78] 9p: ensure err is initialized to 0 in p9_client_read/write

[Greg Kroah-Hartman]

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vincent Bernat <vincent@xxxxxxxxx>

commit 999b8b88c6060adf7a9b7907740ae86ace65291e upstream.

Some use of those functions were providing unitialized values to those
functions. Notably, when reading 0 bytes from an empty file on a 9P
filesystem, the return code of read() was not 0.

Tested with this simple program:

    #include <assert.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <unistd.h>

    int main(int argc, const char **argv)
    {
        assert(argc == 2);
        char buffer[256];
        int fd = open(argv[1], O_RDONLY|O_NOCTTY);
        assert(fd >= 0);
        assert(read(fd, buffer, 0) == 0);
        return 0;
    }

Signed-off-by: Vincent Bernat <vincent@xxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/9p/client.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1541,6 +1541,7 @@ p9_client_read(struct p9_fid *fid, u64 o
 	struct p9_client *clnt = fid->clnt;
 	struct p9_req_t *req;
 	int total = 0;
+	*err = 0;
 
 	p9_debug(P9_DEBUG_9P, ">>> TREAD fid %d offset %llu %d\n",
 		   fid->fid, (unsigned long long) offset, (int)iov_iter_count(to));
@@ -1616,6 +1617,7 @@ p9_client_write(struct p9_fid *fid, u64
 	struct p9_client *clnt = fid->clnt;
 	struct p9_req_t *req;
 	int total = 0;
+	*err = 0;
 
 	p9_debug(P9_DEBUG_9P, ">>> TWRITE fid %d offset %llu count %zd\n",
 				fid->fid, (unsigned long long) offset,


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