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libstore/local-derivation-goal: prohibit creating setuid/setgid binaries #10501

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Apr 18, 2024
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libstore/local-derivation-goal: prohibit creating setuid/setgid binaries #10501

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ba68045
libstore/local-derivation-goal: prohibit creating setuid/setgid binaries
Ma27 Apr 14, 2024
fb9f420
Don't include `linux/` in `#include`
Ericson2314 Apr 15, 2024
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34 changes: 34 additions & 0 deletions src/libstore/linux/fchmodat2-compat.hh
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Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
/*
* Determine the syscall number for `fchmodat2`.
*
* On most platforms this is 452. Exceptions can be found on
* a glibc git checkout via `rg --pcre2 'define __NR_fchmodat2 (?!452)'`.
*
* The problem is that glibc 2.39 and libseccomp 2.5.5 are needed to
* get the syscall number. However, a Nix built against nixpkgs 23.11
* (glibc 2.38) should still have the issue fixed without depending
* on the build environment.
*
* To achieve that, the macros below try to determine the platform and
* set the syscall number which is platform-specific, but
* in most cases 452.
*
* TODO: remove this when 23.11 is EOL and the entire (supported) ecosystem
* is on glibc 2.39.
*/

#if HAVE_SECCOMP
# if defined(__alpha__)
# define NIX_SYSCALL_FCHMODAT2 562
# elif defined(__x86_64__) && SIZE_MAX == 0xFFFFFFFF // x32
# define NIX_SYSCALL_FCHMODAT2 1073742276
# elif defined(__mips__) && defined(__mips64) && defined(_ABIN64) // mips64/n64
# define NIX_SYSCALL_FCHMODAT2 5452
# elif defined(__mips__) && defined(__mips64) && defined(_ABIN32) // mips64/n32
# define NIX_SYSCALL_FCHMODAT2 6452
# elif defined(__mips__) && defined(_ABIO32) // mips32
# define NIX_SYSCALL_FCHMODAT2 4452
# else
# define NIX_SYSCALL_FCHMODAT2 452
# endif
#endif // HAVE_SECCOMP
5 changes: 5 additions & 0 deletions src/libstore/unix/build/local-derivation-goal.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@

/* Includes required for chroot support. */
#if __linux__
# include "fchmodat2-compat.hh"
# include <sys/ioctl.h>
# include <net/if.h>
# include <netinet/ip.h>
Expand Down Expand Up @@ -1672,6 +1673,10 @@ void setupSeccomp()
if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EPERM), SCMP_SYS(fchmodat), 1,
SCMP_A2(SCMP_CMP_MASKED_EQ, (scmp_datum_t) perm, (scmp_datum_t) perm)) != 0)
throw SysError("unable to add seccomp rule");

if (seccomp_rule_add(ctx, SCMP_ACT_ERRNO(EPERM), NIX_SYSCALL_FCHMODAT2, 1,
SCMP_A2(SCMP_CMP_MASKED_EQ, (scmp_datum_t) perm, (scmp_datum_t) perm)) != 0)
throw SysError("unable to add seccomp rule");
}

/* Prevent builders from creating EAs or ACLs. Not all filesystems
Expand Down
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