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8e1071d0ad
The first field in /proc/mounts can be influenced by unprivileged users through the widespread `fusermount` setuid-root program. Example: ``` user$ mkdir ~/mydebugfs user$ export _FUSE_COMMFD=0 user$ fusermount ~/mydebugfs -ononempty,fsname=debugfs user$ grep debugfs /proc/mounts debugfs /home/user/mydebugfs fuse rw,nosuid,nodev,relatime,user_id=1000,group_id=100 0 0 ``` If there is no debugfs already mounted in the system then this can be used by unprivileged users to trick kvm_stat into using a user controlled file system location for obtaining KVM statistics. Even though the root user is not allowed to access non-root FUSE mounts for security reasons, the unprivileged user can unmount the FUSE mount before kvm_stat uses the mounted path. If it wins the race, kvm_stat will read from the location where the FUSE mount resided. Note that the files in debugfs are only opened for reading, so the attacker can cause very large data to be read in by kvm_stat, or fake data to be processed, but there should be no viable way to turn this into a privilege escalation. The fix is simply to use the file system type field instead. Whitespace in the mount path is escaped in /proc/mounts thus no further safety measures in the parsing should be necessary to make this correct. Message-Id: <20221103135927.13656-1-matthias.gerstner@suse.de> Signed-off-by: Matthias Gerstner <matthias.gerstner@suse.de> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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| .. | ||
| accounting | ||
| arch | ||
| bootconfig | ||
| bpf | ||
| build | ||
| certs | ||
| cgroup | ||
| counter | ||
| debugging | ||
| edid | ||
| firewire | ||
| firmware | ||
| gpio | ||
| hv | ||
| iio | ||
| include | ||
| io_uring | ||
| kvm/kvm_stat | ||
| laptop | ||
| leds | ||
| lib | ||
| memory-model | ||
| objtool | ||
| pci | ||
| pcmcia | ||
| perf | ||
| power | ||
| rcu | ||
| scripts | ||
| spi | ||
| testing | ||
| thermal | ||
| time | ||
| tracing | ||
| usb | ||
| verification | ||
| virtio | ||
| vm | ||
| wmi | ||
| Makefile | ||