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lo_setattr() invokes fchmod() in a rarely used code path, so it should be whitelisted or virtiofsd will crash with EBADSYS. Said code path can be triggered for example as follows: On the host, in the shared directory, create a file with the sticky bit set and a security.capability xattr: (1) # touch foo (2) # chmod u+s foo (3) # setcap '' foo Then in the guest let some process truncate that file after it has dropped all of its capabilities (at least CAP_FSETID): int main(int argc, char *argv[]) { capng_setpid(getpid()); capng_clear(CAPNG_SELECT_BOTH); capng_updatev(CAPNG_ADD, CAPNG_PERMITTED | CAPNG_EFFECTIVE, 0); capng_apply(CAPNG_SELECT_BOTH); ftruncate(open(argv[1], O_RDWR), 0); } This will cause the guest kernel to drop the sticky bit (i.e. perform a mode change) as part of the truncate (where FATTR_FH is set), and that will cause virtiofsd to invoke fchmod() instead of fchmodat(). (A similar configuration exists further below with futimens() vs. utimensat(), but the former is not a syscall but just a wrapper for the latter, so no further whitelisting is required.) Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1842667 Reported-by: Qian Cai <caiqian@redhat.com> Cc: qemu-stable@nongnu.org Signed-off-by: Max Reitz <mreitz@redhat.com> Message-Id: <20200608093111.14942-1-mreitz@redhat.com> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> |
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.. | ||
50-qemu-virtiofsd.json.in | ||
buffer.c | ||
fuse_common.h | ||
fuse_i.h | ||
fuse_log.c | ||
fuse_log.h | ||
fuse_lowlevel.c | ||
fuse_lowlevel.h | ||
fuse_misc.h | ||
fuse_opt.c | ||
fuse_opt.h | ||
fuse_signals.c | ||
fuse_virtio.c | ||
fuse_virtio.h | ||
helper.c | ||
Makefile.objs | ||
passthrough_helpers.h | ||
passthrough_ll.c | ||
seccomp.c | ||
seccomp.h |