[Qemu-devel] [PATCH] qemu-io-cmds: Assert that global and nofile commands don't use ct->perms

[Qemu-devel] [PATCH] qemu-io-cmds: Assert that global and nofile commands don't use ct->perms

[Peter Maydell]

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 <peter.maydell@linaro.org>
---
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);
-- 
2.7.4

Re: [Qemu-devel] [PATCH] qemu-io-cmds: Assert that global and nofile commands don't use ct->perms

[Max Reitz]

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On 31.03.2017 15:38, Peter Maydell wrote:
> 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 <peter.maydell@linaro.org>
> ---
> 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.

I think having the assertion in qemuio_add_command() is nicer because if
we break it we will definitely notice just by launching qemu-io.

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

Thanks, applied to my block branch:

https://github.com/XanClic/qemu/commits/block

Max


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