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3898b1b4eb
Filesystem capability support makes it possible to do away with (set)uid-0 based privilege and use capabilities instead. That is, with filesystem support for capabilities but without this present patch, it is (conceptually) possible to manage a system with capabilities alone and never need to obtain privilege via (set)uid-0. Of course, conceptually isn't quite the same as currently possible since few user applications, certainly not enough to run a viable system, are currently prepared to leverage capabilities to exercise privilege. Further, many applications exist that may never get upgraded in this way, and the kernel will continue to want to support their setuid-0 base privilege needs. Where pure-capability applications evolve and replace setuid-0 binaries, it is desirable that there be a mechanisms by which they can contain their privilege. In addition to leveraging the per-process bounding and inheritable sets, this should include suppressing the privilege of the uid-0 superuser from the process' tree of children. The feature added by this patch can be leveraged to suppress the privilege associated with (set)uid-0. This suppression requires CAP_SETPCAP to initiate, and only immediately affects the 'current' process (it is inherited through fork()/exec()). This reimplementation differs significantly from the historical support for securebits which was system-wide, unwieldy and which has ultimately withered to a dead relic in the source of the modern kernel. With this patch applied a process, that is capable(CAP_SETPCAP), can now drop all legacy privilege (through uid=0) for itself and all subsequently fork()'d/exec()'d children with: prctl(PR_SET_SECUREBITS, 0x2f); This patch represents a no-op unless CONFIG_SECURITY_FILE_CAPABILITIES is enabled at configure time. [akpm@linux-foundation.org: fix uninitialised var warning] [serue@us.ibm.com: capabilities: use cap_task_prctl when !CONFIG_SECURITY] Signed-off-by: Andrew G. Morgan <morgan@kernel.org> Acked-by: Serge Hallyn <serue@us.ibm.com> Reviewed-by: James Morris <jmorris@namei.org> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: Paul Moore <paul.moore@hp.com> Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
42 lines
1.8 KiB
C
42 lines
1.8 KiB
C
#ifndef _LINUX_SECUREBITS_H
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#define _LINUX_SECUREBITS_H 1
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#define SECUREBITS_DEFAULT 0x00000000
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/* When set UID 0 has no special privileges. When unset, we support
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inheritance of root-permissions and suid-root executable under
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compatibility mode. We raise the effective and inheritable bitmasks
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*of the executable file* if the effective uid of the new process is
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0. If the real uid is 0, we raise the inheritable bitmask of the
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executable file. */
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#define SECURE_NOROOT 0
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#define SECURE_NOROOT_LOCKED 1 /* make bit-0 immutable */
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/* When set, setuid to/from uid 0 does not trigger capability-"fixes"
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to be compatible with old programs relying on set*uid to loose
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privileges. When unset, setuid doesn't change privileges. */
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#define SECURE_NO_SETUID_FIXUP 2
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#define SECURE_NO_SETUID_FIXUP_LOCKED 3 /* make bit-2 immutable */
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/* When set, a process can retain its capabilities even after
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transitioning to a non-root user (the set-uid fixup suppressed by
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bit 2). Bit-4 is cleared when a process calls exec(); setting both
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bit 4 and 5 will create a barrier through exec that no exec()'d
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child can use this feature again. */
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#define SECURE_KEEP_CAPS 4
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#define SECURE_KEEP_CAPS_LOCKED 5 /* make bit-4 immutable */
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/* Each securesetting is implemented using two bits. One bit specify
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whether the setting is on or off. The other bit specify whether the
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setting is fixed or not. A setting which is fixed cannot be changed
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from user-level. */
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#define issecure_mask(X) (1 << (X))
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#define issecure(X) (issecure_mask(X) & current->securebits)
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#define SECURE_ALL_BITS (issecure_mask(SECURE_NOROOT) | \
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issecure_mask(SECURE_NO_SETUID_FIXUP) | \
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issecure_mask(SECURE_KEEP_CAPS))
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#define SECURE_ALL_LOCKS (SECURE_ALL_BITS << 1)
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#endif /* !_LINUX_SECUREBITS_H */
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