Read-only sandbox paths mounts (Linux) #13315
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tomberek
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edolstra
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Signed-off-by: Samuli Thomasson <samuli.thomasson@pm.me>
some of the functional tests that run config check wouldn't tolerate some oddities in `PATH`, something like a null string entry (e.g. `::` in the middle or a trailing `:`) I think. This allows the test pass. Signed-off-by: Samuli Thomasson <samuli.thomasson@pm.me>
Signed-off-by: Samuli Thomasson <samuli.thomasson@pm.me>
Signed-off-by: Samuli Thomasson <samuli.thomasson@pm.me>
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| #ifdef __linux__ | ||
| /* Options to set when readOnly=true */ | ||
| constexpr static MountOpt readOnlyDefaults[] = { ro, nodev, noexec, nosuid, noatime }; |
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Hm, seems odd to have "readOnly" imply noexec, noatime etc. I would expect a readonly mount to still be executable by default.
| strictatime = MS_STRICTATIME, /* overrides any atime/relatime */ | ||
| private_ = MS_PRIVATE, | ||
| slave = MS_SLAVE, | ||
| unbindable = MS_UNBINDABLE |
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Not sure if all of these mount options make sense to expose. In particular, the mount propagation flags seem a bit scary. We don't want the builder to be able to have mounts propagate out of the sandbox...
We should probably set MS_NOSUID unconditionally since it's nice for security. Though unfortunately it doesn't prevent the creation of suid binaries.
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Motivation
This extends the
sandbox-pathssyntax to allowthe extra optional suffixextended JSON syntax for marking that path so as to be mounted read-only in the sandbox.:roThe suffix is excluded from the mounted source or target path. It will only cause the mountThe new "readOnly" option enablesMS_RDONLYflag to be set.MS_RDONLYand a few other mount-point flags for the affected bind-mount.Context
...well, technically we make then another
mount(2)call on the target path right after mounting the path for the first time, in order to do a second mount (or rather remount,MS_REMOUNT) withMS_RDONLY. For some reason singlemountsyscall can't both create a new bind-mount and assign the read-only flag to it (its mount-point really) ... or propagation properties for that matter.The
mount(8)cli fromutil-linuxabstracts over this with a second syscall as necessary as well (more even sometimes, it seems).There's a better, modern API since about linux 5.12 with
open_tree(),mount_setattr()andmove_mount(). Probably doesn't really make a difference until there's some need or want for those features though.One of the commits (2eaca52) is not related to to the bulk of the changes in this. it's a small change to fix a certain edge-case (think user launching
nixor running tests with aPATHthat still works, for all intents and purposes, but looks like it fell through a slipstream portal sideways).add 👍 to pull requests you find important.
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