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Subject[PATCH RFC v2 0/4] coredump: mitigate privilege escalation of process coredump
Date
v2
==

Patch 02 conflicted with commit 92307383082d("coredump: Don't perform
any cleanups before dumping core") which I didn't have in my tree. V2
just changes the hunk

+#define PF_SUID 0x00000008

To

+#define PF_SUID 0x01000000

To merge cleanly. Other than that, it is the same patch as v1.

v1
==

A set-uid executable might be a vector to privilege escalation if the
system configures the coredump file name pattern as a relative
directory destiny. The full description of the vulnerability and
a demonstration of how we can exploit it can be found at [1].

This patch series adds a PF_SUID flag to the process in execve if it is
set-[ug]id binary and elevates the new image's privileges.

In the do_coredump function, we check if:

1) We have the SUID_FLAG set
2) We have CAP_SYS_ADMIN (the process might have decreased its
privileges)
3) The current directory is owned by root (the current code already
checks for core_pattern being a relative path).
4) non-privileged users don't have permission to write to the current
directory.

If all four conditions match, we set the need_suid_safe flag.

An alternative implementation (and more elegant IMO) would be saving
the fsuid and fsgid of the process in the task_struct before loading the
new image to the memory. But this approach would add eight bytes to all
task_struct instances where only a tiny fraction of the processes need
it and under a configuration that not all (most?) distributions don't
adopt by default.

Wander Lairson Costa (4):
exec: add a flag indicating if an exec file is a suid/sgid
process: add the PF_SUID flag
coredump: mitigate privilege escalation of process coredump
exec: only set the suid flag if the current proc isn't root

fs/coredump.c | 15 +++++++++++++++
fs/exec.c | 10 ++++++++++
include/linux/binfmts.h | 6 +++++-
include/linux/sched.h | 1 +
kernel/fork.c | 2 ++
5 files changed, 33 insertions(+), 1 deletion(-)

--
2.27.0

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