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* treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36Thomas Gleixner2019-05-241-5/+1
| | | | | | | | | | | | | | | | | | | | | | Based on 1 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public licence as published by the free software foundation either version 2 of the licence or at your option any later version extracted by the scancode license scanner the SPDX license identifier GPL-2.0-or-later has been chosen to replace the boilerplate/reference in 114 file(s). Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Allison Randal <allison@lohutok.net> Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org> Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190520170857.552531963@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
* lib/assoc_array.c: mark expected switch fall-throughGustavo A. R. Silva2019-03-071-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | In preparation to enabling -Wimplicit-fallthrough, mark switch cases where we are expecting to fall through. This patch fixes the following warning: lib/assoc_array.c: In function `assoc_array_delete': lib/assoc_array.c:1110:3: warning: this statement may fall through [-Wimplicit-fallthrough=] for (slot = 0; slot < ASSOC_ARRAY_FAN_OUT; slot++) { ^~~ lib/assoc_array.c:1118:2: note: here case assoc_array_walk_tree_empty: ^~~~ Warning level 3 was used: -Wimplicit-fallthrough=3 This patch is part of the ongoing efforts to enable -Wimplicit-fallthrough. Link: http://lkml.kernel.org/r/20190212212206.GA16378@embeddedor Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* assoc_array: Fix shortcut creationDavid Howells2019-02-151-3/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | Fix the creation of shortcuts for which the length of the index key value is an exact multiple of the machine word size. The problem is that the code that blanks off the unused bits of the shortcut value malfunctions if the number of bits in the last word equals machine word size. This is due to the "<<" operator being given a shift of zero in this case, and so the mask that should be all zeros is all ones instead. This causes the subsequent masking operation to clear everything rather than clearing nothing. Ordinarily, the presence of the hash at the beginning of the tree index key makes the issue very hard to test for, but in this case, it was encountered due to a development mistake that caused the hash output to be either 0 (keyring) or 1 (non-keyring) only. This made it susceptible to the keyctl/unlink/valid test in the keyutils package. The fix is simply to skip the blanking if the shift would be 0. For example, an index key that is 64 bits long would produce a 0 shift and thus a 'blank' of all 1s. This would then be inverted and AND'd onto the index_key, incorrectly clearing the entire last word. Fixes: 3cb989501c26 ("Add a generic associative array implementation.") Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: James Morris <james.morris@microsoft.com>
* lib/assoc_array: Remove smp_read_barrier_depends()Paul E. McKenney2017-12-041-25/+12
| | | | | | | | | | | | | Now that smp_read_barrier_depends() is implied by READ_ONCE(), the several smp_read_barrier_depends() calls may be removed from lib/assoc_array.c. This commit makes this change and marks the READ_ONCE() calls that head address dependencies. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Kuleshov <kuleshovmail@gmail.com> Cc: David Howells <dhowells@redhat.com>
* Merge branch 'linus' into locking/core, to resolve conflictsIngo Molnar2017-11-071-34/+17
|\ | | | | | | | | | | | | | | | | | | Conflicts: include/linux/compiler-clang.h include/linux/compiler-gcc.h include/linux/compiler-intel.h include/uapi/linux/stddef.h Signed-off-by: Ingo Molnar <mingo@kernel.org>
| * assoc_array: Fix a buggy node-splitting caseDavid Howells2017-10-281-34/+17
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This fixes CVE-2017-12193. Fix a case in the assoc_array implementation in which a new leaf is added that needs to go into a node that happens to be full, where the existing leaves in that node cluster together at that level to the exclusion of new leaf. What needs to happen is that the existing leaves get moved out to a new node, N1, at level + 1 and the existing node needs replacing with one, N0, that has pointers to the new leaf and to N1. The code that tries to do this gets this wrong in two ways: (1) The pointer that should've pointed from N0 to N1 is set to point recursively to N0 instead. (2) The backpointer from N0 needs to be set correctly in the case N0 is either the root node or reached through a shortcut. Fix this by removing this path and using the split_node path instead, which achieves the same end, but in a more general way (thanks to Eric Biggers for spotting the redundancy). The problem manifests itself as: BUG: unable to handle kernel NULL pointer dereference at 0000000000000010 IP: assoc_array_apply_edit+0x59/0xe5 Fixes: 3cb989501c26 ("Add a generic associative array implementation.") Reported-and-tested-by: WU Fan <u3536072@connect.hku.hk> Signed-off-by: David Howells <dhowells@redhat.com> Cc: stable@vger.kernel.org [v3.13-rc1+] Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* | locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns ↵Mark Rutland2017-10-251-10/+10
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | to READ_ONCE()/WRITE_ONCE() Please do not apply this to mainline directly, instead please re-run the coccinelle script shown below and apply its output. For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't harmful, and changing them results in churn. However, for some features, the read/write distinction is critical to correct operation. To distinguish these cases, separate read/write accessors must be used. This patch migrates (most) remaining ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following coccinelle script: ---- // Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and // WRITE_ONCE() // $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: viro@zeniv.linux.org.uk Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
* assoc_array: fix path to assoc_array documentationAlexander Kuleshov2017-08-301-1/+1
| | | | | Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
* assoc_array: don't call compare_object() on a nodeJerome Marchand2016-04-061-1/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Changes since V1: fixed the description and added KASan warning. In assoc_array_insert_into_terminal_node(), we call the compare_object() method on all non-empty slots, even when they're not leaves, passing a pointer to an unexpected structure to compare_object(). Currently it causes an out-of-bound read access in keyring_compare_object detected by KASan (see below). The issue is easily reproduced with keyutils testsuite. Only call compare_object() when the slot is a leave. KASan warning: ================================================================== BUG: KASAN: slab-out-of-bounds in keyring_compare_object+0x213/0x240 at addr ffff880060a6f838 Read of size 8 by task keyctl/1655 ============================================================================= BUG kmalloc-192 (Not tainted): kasan: bad access detected ----------------------------------------------------------------------------- Disabling lock debugging due to kernel taint INFO: Allocated in assoc_array_insert+0xfd0/0x3a60 age=69 cpu=1 pid=1647 ___slab_alloc+0x563/0x5c0 __slab_alloc+0x51/0x90 kmem_cache_alloc_trace+0x263/0x300 assoc_array_insert+0xfd0/0x3a60 __key_link_begin+0xfc/0x270 key_create_or_update+0x459/0xaf0 SyS_add_key+0x1ba/0x350 entry_SYSCALL_64_fastpath+0x12/0x76 INFO: Slab 0xffffea0001829b80 objects=16 used=8 fp=0xffff880060a6f550 flags=0x3fff8000004080 INFO: Object 0xffff880060a6f740 @offset=5952 fp=0xffff880060a6e5d1 Bytes b4 ffff880060a6f730: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f740: d1 e5 a6 60 00 88 ff ff 0e 00 00 00 00 00 00 00 ...`............ Object ffff880060a6f750: 02 cf 8e 60 00 88 ff ff 02 c0 8e 60 00 88 ff ff ...`.......`.... Object ffff880060a6f760: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f770: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f790: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f7a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f7b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f7c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f7d0: 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f7e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Object ffff880060a6f7f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ CPU: 0 PID: 1655 Comm: keyctl Tainted: G B 4.5.0-rc4-kasan+ #291 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 0000000000000000 000000001b2800b4 ffff880060a179e0 ffffffff81b60491 ffff88006c802900 ffff880060a6f740 ffff880060a17a10 ffffffff815e2969 ffff88006c802900 ffffea0001829b80 ffff880060a6f740 ffff880060a6e650 Call Trace: [<ffffffff81b60491>] dump_stack+0x85/0xc4 [<ffffffff815e2969>] print_trailer+0xf9/0x150 [<ffffffff815e9454>] object_err+0x34/0x40 [<ffffffff815ebe50>] kasan_report_error+0x230/0x550 [<ffffffff819949be>] ? keyring_get_key_chunk+0x13e/0x210 [<ffffffff815ec62d>] __asan_report_load_n_noabort+0x5d/0x70 [<ffffffff81994cc3>] ? keyring_compare_object+0x213/0x240 [<ffffffff81994cc3>] keyring_compare_object+0x213/0x240 [<ffffffff81bc238c>] assoc_array_insert+0x86c/0x3a60 [<ffffffff81bc1b20>] ? assoc_array_cancel_edit+0x70/0x70 [<ffffffff8199797d>] ? __key_link_begin+0x20d/0x270 [<ffffffff8199786c>] __key_link_begin+0xfc/0x270 [<ffffffff81993389>] key_create_or_update+0x459/0xaf0 [<ffffffff8128ce0d>] ? trace_hardirqs_on+0xd/0x10 [<ffffffff81992f30>] ? key_type_lookup+0xc0/0xc0 [<ffffffff8199e19d>] ? lookup_user_key+0x13d/0xcd0 [<ffffffff81534763>] ? memdup_user+0x53/0x80 [<ffffffff819983ea>] SyS_add_key+0x1ba/0x350 [<ffffffff81998230>] ? key_get_type_from_user.constprop.6+0xa0/0xa0 [<ffffffff828bcf4e>] ? retint_user+0x18/0x23 [<ffffffff8128cc7e>] ? trace_hardirqs_on_caller+0x3fe/0x580 [<ffffffff81004017>] ? trace_hardirqs_on_thunk+0x17/0x19 [<ffffffff828bc432>] entry_SYSCALL_64_fastpath+0x12/0x76 Memory state around the buggy address: ffff880060a6f700: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00 ffff880060a6f780: 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc >ffff880060a6f800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ^ ffff880060a6f880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff880060a6f900: fc fc fc fc fc fc 00 00 00 00 00 00 00 00 00 00 ================================================================== Signed-off-by: Jerome Marchand <jmarchan@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> cc: stable@vger.kernel.org
* assoc_array: Include rcupdate.h for call_rcu() definitionPranith Kumar2015-01-071-0/+1
| | | | | | | | | | | | | | | | | | Include rcupdate.h header to provide call_rcu() definition. This was implicitly being provided by slab.h file which include srcu.h somewhere in its include hierarchy which in-turn included rcupdate.h. Lately, tinification effort added support to remove srcu entirely because of which we are encountering build errors like lib/assoc_array.c: In function 'assoc_array_apply_edit': lib/assoc_array.c:1426:2: error: implicit declaration of function 'call_rcu' [-Werror=implicit-function-declaration] cc1: some warnings being treated as errors Fix these by including rcupdate.h explicitly. Signed-off-by: Pranith Kumar <bobby.prani@gmail.com> Reported-by: Scott Wood <scottwood@freescale.com>
* KEYS: Fix termination condition in assoc array garbage collectionDavid Howells2014-09-121-1/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This fixes CVE-2014-3631. It is possible for an associative array to end up with a shortcut node at the root of the tree if there are more than fan-out leaves in the tree, but they all crowd into the same slot in the lowest level (ie. they all have the same first nibble of their index keys). When assoc_array_gc() returns back up the tree after scanning some leaves, it can fall off of the root and crash because it assumes that the back pointer from a shortcut (after label ascend_old_tree) must point to a normal node - which isn't true of a shortcut node at the root. Should we find we're ascending rootwards over a shortcut, we should check to see if the backpointer is zero - and if it is, we have completed the scan. This particular bug cannot occur if the root node is not a shortcut - ie. if you have fewer than 17 keys in a keyring or if you have at least two keys that sit into separate slots (eg. a keyring and a non keyring). This can be reproduced by: ring=`keyctl newring bar @s` for ((i=1; i<=18; i++)); do last_key=`keyctl newring foo$i $ring`; done keyctl timeout $last_key 2 Doing this: echo 3 >/proc/sys/kernel/keys/gc_delay first will speed things up. If we do fall off of the top of the tree, we get the following oops: BUG: unable to handle kernel NULL pointer dereference at 0000000000000018 IP: [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540 PGD dae15067 PUD cfc24067 PMD 0 Oops: 0000 [#1] SMP Modules linked in: xt_nat xt_mark nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_rpfilter ip6t_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_ni CPU: 0 PID: 26011 Comm: kworker/0:1 Not tainted 3.14.9-200.fc20.x86_64 #1 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 Workqueue: events key_garbage_collector task: ffff8800918bd580 ti: ffff8800aac14000 task.ti: ffff8800aac14000 RIP: 0010:[<ffffffff8136cea7>] [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540 RSP: 0018:ffff8800aac15d40 EFLAGS: 00010206 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff8800aaecacc0 RDX: ffff8800daecf440 RSI: 0000000000000001 RDI: ffff8800aadc2bc0 RBP: ffff8800aac15da8 R08: 0000000000000001 R09: 0000000000000003 R10: ffffffff8136ccc7 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000070 R15: 0000000000000001 FS: 0000000000000000(0000) GS:ffff88011fc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: 0000000000000018 CR3: 00000000db10d000 CR4: 00000000000006f0 Stack: ffff8800aac15d50 0000000000000011 ffff8800aac15db8 ffffffff812e2a70 ffff880091a00600 0000000000000000 ffff8800aadc2bc3 00000000cd42c987 ffff88003702df20 ffff88003702dfa0 0000000053b65c09 ffff8800aac15fd8 Call Trace: [<ffffffff812e2a70>] ? keyring_detect_cycle_iterator+0x30/0x30 [<ffffffff812e3e75>] keyring_gc+0x75/0x80 [<ffffffff812e1424>] key_garbage_collector+0x154/0x3c0 [<ffffffff810a67b6>] process_one_work+0x176/0x430 [<ffffffff810a744b>] worker_thread+0x11b/0x3a0 [<ffffffff810a7330>] ? rescuer_thread+0x3b0/0x3b0 [<ffffffff810ae1a8>] kthread+0xd8/0xf0 [<ffffffff810ae0d0>] ? insert_kthread_work+0x40/0x40 [<ffffffff816ffb7c>] ret_from_fork+0x7c/0xb0 [<ffffffff810ae0d0>] ? insert_kthread_work+0x40/0x40 Code: 08 4c 8b 22 0f 84 bf 00 00 00 41 83 c7 01 49 83 e4 fc 41 83 ff 0f 4c 89 65 c0 0f 8f 5a fe ff ff 48 8b 45 c0 4d 63 cf 49 83 c1 02 <4e> 8b 34 c8 4d 85 f6 0f 84 be 00 00 00 41 f6 c6 01 0f 84 92 RIP [<ffffffff8136cea7>] assoc_array_gc+0x2f7/0x540 RSP <ffff8800aac15d40> CR2: 0000000000000018 ---[ end trace 1129028a088c0cbd ]--- Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Don Zickus <dzickus@redhat.com> Signed-off-by: James Morris <james.l.morris@oracle.com>
* KEYS: Fix use-after-free in assoc_array_gc()David Howells2014-09-031-1/+1
| | | | | | | | | | | | | | | | An edit script should be considered inaccessible by a function once it has called assoc_array_apply_edit() or assoc_array_cancel_edit(). However, assoc_array_gc() is accessing the edit script just after the gc_complete: label. Reported-by: Andreea-Cristina Bernat <bernat.ada@gmail.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Andreea-Cristina Bernat <bernat.ada@gmail.com> cc: shemming@brocade.com cc: paulmck@linux.vnet.ibm.com Cc: stable@vger.kernel.org Signed-off-by: James Morris <james.l.morris@oracle.com>
* assoc_array: remove global variableStephen Hemminger2014-01-231-1/+1
| | | | | | | | | The associative array code creates unnecessary and potentially problematic global variable 'status'. Remove it since never used. Signed-off-by: Stephen Hemminger <stephen@networkplumber.org> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* KEYS: Fix multiple key add into associative arrayDavid Howells2013-12-021-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If sufficient keys (or keyrings) are added into a keyring such that a node in the associative array's tree overflows (each node has a capacity N, currently 16) and such that all N+1 keys have the same index key segment for that level of the tree (the level'th nibble of the index key), then assoc_array_insert() calls ops->diff_objects() to indicate at which bit position the two index keys vary. However, __key_link_begin() passes a NULL object to assoc_array_insert() with the intention of supplying the correct pointer later before we commit the change. This means that keyring_diff_objects() is given a NULL pointer as one of its arguments which it does not expect. This results in an oops like the attached. With the previous patch to fix the keyring hash function, this can be forced much more easily by creating a keyring and only adding keyrings to it. Add any other sort of key and a different insertion path is taken - all 16+1 objects must want to cluster in the same node slot. This can be tested by: r=`keyctl newring sandbox @s` for ((i=0; i<=16; i++)); do keyctl newring ring$i $r; done This should work fine, but oopses when the 17th keyring is added. Since ops->diff_objects() is always called with the first pointer pointing to the object to be inserted (ie. the NULL pointer), we can fix the problem by changing the to-be-inserted object pointer to point to the index key passed into assoc_array_insert() instead. Whilst we're at it, we also switch the arguments so that they are the same as for ->compare_object(). BUG: unable to handle kernel NULL pointer dereference at 0000000000000088 IP: [<ffffffff81191ee4>] hash_key_type_and_desc+0x18/0xb0 ... RIP: 0010:[<ffffffff81191ee4>] hash_key_type_and_desc+0x18/0xb0 ... Call Trace: [<ffffffff81191f9d>] keyring_diff_objects+0x21/0xd2 [<ffffffff811f09ef>] assoc_array_insert+0x3b6/0x908 [<ffffffff811929a7>] __key_link_begin+0x78/0xe5 [<ffffffff81191a2e>] key_create_or_update+0x17d/0x36a [<ffffffff81192e0a>] SyS_add_key+0x123/0x183 [<ffffffff81400ddb>] tracesys+0xdd/0xe2 Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: Stephen Gallagher <sgallagh@redhat.com>
* KEYS: Expand the capacity of a keyringDavid Howells2013-09-241-0/+1
| | | | | | | | | | | | | | | | | | | | Expand the capacity of a keyring to be able to hold a lot more keys by using the previously added associative array implementation. Currently the maximum capacity is: (PAGE_SIZE - sizeof(header)) / sizeof(struct key *) which, on a 64-bit system, is a little more 500. However, since this is being used for the NFS uid mapper, we need more than that. The new implementation gives us effectively unlimited capacity. With some alterations, the keyutils testsuite runs successfully to completion after this patch is applied. The alterations are because (a) keyrings that are simply added to no longer appear ordered and (b) some of the errors have changed a bit. Signed-off-by: David Howells <dhowells@redhat.com>
* Add a generic associative array implementation.David Howells2013-09-241-0/+1745
Add a generic associative array implementation that can be used as the container for keyrings, thereby massively increasing the capacity available whilst also speeding up searching in keyrings that contain a lot of keys. This may also be useful in FS-Cache for tracking cookies. Documentation is added into Documentation/associative_array.txt Some of the properties of the implementation are: (1) Objects are opaque pointers. The implementation does not care where they point (if anywhere) or what they point to (if anything). [!] NOTE: Pointers to objects _must_ be zero in the two least significant bits. (2) Objects do not need to contain linkage blocks for use by the array. This permits an object to be located in multiple arrays simultaneously. Rather, the array is made up of metadata blocks that point to objects. (3) Objects are labelled as being one of two types (the type is a bool value). This information is stored in the array, but has no consequence to the array itself or its algorithms. (4) Objects require index keys to locate them within the array. (5) Index keys must be unique. Inserting an object with the same key as one already in the array will replace the old object. (6) Index keys can be of any length and can be of different lengths. (7) Index keys should encode the length early on, before any variation due to length is seen. (8) Index keys can include a hash to scatter objects throughout the array. (9) The array can iterated over. The objects will not necessarily come out in key order. (10) The array can be iterated whilst it is being modified, provided the RCU readlock is being held by the iterator. Note, however, under these circumstances, some objects may be seen more than once. If this is a problem, the iterator should lock against modification. Objects will not be missed, however, unless deleted. (11) Objects in the array can be looked up by means of their index key. (12) Objects can be looked up whilst the array is being modified, provided the RCU readlock is being held by the thread doing the look up. The implementation uses a tree of 16-pointer nodes internally that are indexed on each level by nibbles from the index key. To improve memory efficiency, shortcuts can be emplaced to skip over what would otherwise be a series of single-occupancy nodes. Further, nodes pack leaf object pointers into spare space in the node rather than making an extra branch until as such time an object needs to be added to a full node. Signed-off-by: David Howells <dhowells@redhat.com>
generated by cgit v1.2.3 (git 2.25.1) at 2024-11-22 11:58:08 +0000