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[Qemu-devel] [PATCH] qemu-io-cmds: Assert that global and nofile command

From: Peter Maydell
Subject: [Qemu-devel] [PATCH] qemu-io-cmds: Assert that global and nofile commands don't use ct->perms
Date: Fri, 31 Mar 2017 14:38:49 +0100

It would be a bug for a command with the CMD_NOFILE_OK or
CMD_FLAG_GLOBAL flags set to also set the ct->perms field,
because the former says "OK for a file not to be open"
but the latter is a check on a file.

Add an assertion in qemuio_add_command() so we can catch that
sort of buggy command definition immediately rather than it
being a bug that only manifests when a particular set of
command line options is used.

(Coverity gets confused about this (CID 1371723) and reports
that we might dereference a NULL blk pointer in this case,
because it can't tell that that code path never happens with
the cmdinfo_t that we have. This commit won't help unconfuse
it, but it does fix the underlying issue.)

Signed-off-by: Peter Maydell <address@hidden>
We could also try to add some kind of assert in command() to
persuade coverity that it can't get there with a NULL block
and ct->perms non-zero, but I think I'd rather just mark the
issue as a false-positive and move on.

 qemu-io-cmds.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 2c48f9c..883f53b 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -35,6 +35,13 @@ static int compare_cmdname(const void *a, const void *b)
 void qemuio_add_command(const cmdinfo_t *ci)
+    /* ci->perm assumes a file is open, but the GLOBAL and NOFILE_OK
+     * flags allow it not to be, so that combination is invalid.
+     * Catch it now rather than letting it manifest as a crash if a
+     * particular set of command line options are used.
+     */
+    assert(ci->perm == 0 ||
+           (ci->flags & (CMD_FLAG_GLOBAL | CMD_NOFILE_OK)) == 0);
     cmdtab = g_renew(cmdinfo_t, cmdtab, ++ncmds);
     cmdtab[ncmds - 1] = *ci;
     qsort(cmdtab, ncmds, sizeof(*cmdtab), compare_cmdname);

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