[xen staging] tools/xenstored: Don't assume errno will not be overwritten in lu_arch()

[patchbot@xxxxxxx]

commit e066ca5acc2ee3b5db5c005e1a548b05e753e07d
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Fri Jul 30 16:14:14 2021 +0100
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Jul 30 16:14:39 2021 +0100

    tools/xenstored: Don't assume errno will not be overwritten in lu_arch()
    
    At the moment, do_control_lu() will set errno to 0 before calling
    lu_arch() and then check errno. The expectation is nothing in lu_arch()
    will change the value unless there is an error.
    
    However, per errno(3), a function that succeeds is allowed to change
    errno. In fact, syslog() will overwrite errno if the logs are rotated
    at the time it is called.
    
    To prevent any further issue, errno is now always set before
    returning NULL.
    
    Additionally, errno is only checked when returning NULL so the client
    can see the error message if there is any.
    
    Reported-by: Michael Kurth <mku@xxxxxxxxxx>
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
---
 tools/xenstore/xenstored_control.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/xenstore/xenstored_control.c 
b/tools/xenstore/xenstored_control.c
index 6b68b79faa..7b4300ef77 100644
--- a/tools/xenstore/xenstored_control.c
+++ b/tools/xenstore/xenstored_control.c
@@ -324,6 +324,7 @@ static const char *lu_binary_alloc(const void *ctx, struct 
connection *conn,
        lu_status->kernel_size = size;
        lu_status->kernel_off = 0;
 
+       errno = 0;
        return NULL;
 }
 
@@ -339,6 +340,7 @@ static const char *lu_binary_save(const void *ctx, struct 
connection *conn,
        memcpy(lu_status->kernel + lu_status->kernel_off, data, size);
        lu_status->kernel_off += size;
 
+       errno = 0;
        return NULL;
 }
 
@@ -413,6 +415,7 @@ static const char *lu_binary(const void *ctx, struct 
connection *conn,
        if (!lu_status->filename)
                return "Allocation failure.";
 
+       errno = 0;
        return NULL;
 }
 
@@ -798,9 +801,8 @@ static int do_control_lu(void *ctx, struct connection *conn,
                if (!ret)
                        return errno;
        } else {
-               errno = 0;
                ret = lu_arch(ctx, conn, vec, num);
-               if (errno)
+               if (!ret && errno)
                        return errno;
        }
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging