Set groups when dropping privileges to not leak supplementary group access #1202
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…ccess Changing the real and effective user/group IDs and the saved set-user/group-ID is not enough to get rid of intial access permissions. The list of groups must be cleared also, otherwise a process changing from, e.g. `root:root` to `nobody:nobody` retains rights to access `:wheel` files (assuming `root` is a member of the `wheel` group). For example: ``` # id uid=0(root) gid=0(wheel) groups=0(wheel), 2(kmem), 3(sys), 4(tty), 5(operator), 20(staff), 31(guest) # ./yggdrasil -autoconf -logto /dev/null -user nobody & [1] 4337 # ps -o command,user,group,supgrp -U nobody COMMAND USER GROUP SUPGRP ./yggdrasil -aut nobody nobody wheel,kmem,sys,tty,operator,staff,guest ``` Fix that so the process runs as mere ``` COMMAND USER GROUP SUPGRP ./yggdrasil -aut nobody nobody nobody ``` Fixes yggdrasil-network#927.
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| @@ -63,6 +66,9 @@ | |||
| } | |||
| } else if u != nil { | |||
| gid, _ := strconv.ParseUint(u.Gid, 10, 32) | |||
| if err := syscall.Setgroups([]int{int(uint32(gid))}); err != nil { | |||
Check failure
Code scanning / CodeQL
Incorrect conversion between integer types High
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I have deliberately copy-pasted what the current code does without alteration.
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This is a minimally invasive security fix for the currently, imho, convoluted and overly complex I simplified it to match the standard idiom used by dozens of programs in the OpenBSD base system, but that should be a separate change. |
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- Use unambiguous variable names (w/o package name conflict). - Fail on invalid input such as the empty string or `:`. - Do not change group without user, i.e. fail on `:group`. - Parse input using mnemonic APIs. - Do not juggle between integer types. - Unset supplementary groups. - Use setres[ug]id(2) to match the idiom of OpenBSD base programs. Includes/Supersedes yggdrasil-network#1202. Fixes yggdrasil-network#927. I only tested on OpenBSD (so far), hence the split, but other systems should just work.
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- Use unambiguous variable names (w/o package name conflict). - Fail on invalid input such as the empty string or `:`. - Do not change group without user, i.e. fail on `:group`. - Parse input using mnemonic APIs. - Do not juggle between integer types. - Unset supplementary groups. - Use setres[ug]id(2) to match the idiom of OpenBSD base programs. Includes/Supersedes yggdrasil-network#1202. Fixes yggdrasil-network#927. I only tested on OpenBSD (so far), hence the split, but other systems should just work.
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- Use unambiguous variable names (w/o package name conflict). - Fail on invalid input such as the empty string or `:`. - Do not change group without user, i.e. fail on `:group`. - Parse input using mnemonic APIs. - Do not juggle between integer types. - Unset supplementary groups. - Use set[ug]id(2) to follow the idiom of OpenBSD base programs. (cannot use setres[ug]id(2) as macOS does not have them.) Includes/Supersedes #1202. Fixes #927. I only tested on OpenBSD (so far), but other systems should just work.
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Changing the real and effective user/group IDs and the saved set-user/group-ID is not enough to get rid of intial access permissions.
The list of groups must be cleared also, otherwise a process changing from, e.g.
root:roottonobody:nobodyretains rights to access:wheelfiles (assumingrootis a member of thewheelgroup).For example:
Fix that so the process runs as mere
Fixes #927.