Re: [libvirt] [PATCH] lib: Avoid double free when passing FDs with virCommandPassFD()

If an FD is passed into a child using: virCommandPassFD(cmd, fd, VIR_COMMAND_PASS_FD_CLOSE_PARENT); then the parent should refrain from touching @fd thereafter. This is even documented in virCommandPassFD() comment. The reason is that either at virCommandRun()/virCommandRunAsync() or virCommandFree() time the @fd will be closed. Closing it earlier, e.g. right after virCommandPassFD() call might result in undesired results. Another thread might open a file and receive the same FD which is then unexpectedly closed by virCommandFree() or virCommandRun(). Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/qemu/qemu_command.c | 10 ++++++---- src/util/virpolkit.c | 1 + tests/commandtest.c | 2 +- 3 files changed, 8 insertions(+), 5 deletions(-) diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index bf1fb539b1..92bd1524db 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -8978,17 +8978,19 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver, if (qemuSecuritySetTapFDLabel(driver->securityManager, def, tapfd[i]) < 0) goto cleanup; - virCommandPassFD(cmd, tapfd[i], - VIR_COMMAND_PASS_FD_CLOSE_PARENT); if (virAsprintf(&tapfdName[i], "%d", tapfd[i]) < 0) goto cleanup; + virCommandPassFD(cmd, tapfd[i], + VIR_COMMAND_PASS_FD_CLOSE_PARENT); + tapfd[i] = -1; } for (i = 0; i < vhostfdSize; i++) { - virCommandPassFD(cmd, vhostfd[i], - VIR_COMMAND_PASS_FD_CLOSE_PARENT); if (virAsprintf(&vhostfdName[i], "%d", vhostfd[i]) < 0) goto cleanup; + virCommandPassFD(cmd, vhostfd[i], + VIR_COMMAND_PASS_FD_CLOSE_PARENT); + vhostfd[i] = -1;

} if (chardev)