linux.git/mm, branch v2.6.27-rc4

mm: xip/ext2 fix block allocation race

2008-08-20T22:40:32+00:00

XIP can call into get_xip_mem concurrently with the same file,offset with
create=1.  This usually maps down to get_block, which expects the page
lock to prevent such a situation.  This causes ext2 to explode for one
reason or another.

Serialise those calls for the moment.  For common usages today, I suspect
get_xip_mem rarely is called to create new blocks.  In future as XIP
technologies evolve we might need to look at which operations require
scalability, and rework the locking to suit.

Signed-off-by: Nick Piggin 
Cc: Jared Hulbert 
Acked-by: Carsten Otte 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: xip fix fault vs sparse page invalidate race

2008-08-20T22:40:32+00:00

XIP has a race between sparse pages being inserted into page tables, and
sparse pages being zapped when its time to put a non-sparse page in.

What can happen is that a process can be left with a dangling sparse page
in a MAP_SHARED mapping, while the rest of the world sees the non-sparse
version.  Ie.  data corruption.

Guard these operations with a seqlock, making fault-in-sparse-pages the
slowpath, and try-to-unmap-sparse-pages the fastpath.

Signed-off-by: Nick Piggin 
Cc: Jared Hulbert 
Acked-by: Carsten Otte 
Cc: Hugh Dickins 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: dirty page tracking race fix

2008-08-20T22:40:32+00:00

There is a race with dirty page accounting where a page may not properly
be accounted for.

clear_page_dirty_for_io() calls page_mkclean; then TestClearPageDirty.

page_mkclean walks the rmaps for that page, and for each one it cleans and
write protects the pte if it was dirty.  It uses page_check_address to
find the pte.  That function has a shortcut to avoid the ptl if the pte is
not present.  Unfortunately, the pte can be switched to not-present then
back to present by other code while holding the page table lock -- this
should not be a signal for page_mkclean to ignore that pte, because it may
be dirty.

For example, powerpc64's set_pte_at will clear a previously present pte
before setting it to the desired value.  There may also be other code in
core mm or in arch which do similar things.

The consequence of the bug is loss of data integrity due to msync, and
loss of dirty page accounting accuracy.  XIP's __xip_unmap could easily
also be unreliable (depending on the exact XIP locking scheme), which can
lead to data corruption.

Fix this by having an option to always take ptl to check the pte in
page_check_address.

It's possible to retain this optimization for page_referenced and
try_to_unmap.

Signed-off-by: Nick Piggin 
Cc: Jared Hulbert 
Cc: Carsten Otte 
Cc: Hugh Dickins 
Acked-by: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

bootmem: fix aligning of node-relative indexes and offsets

2008-08-20T22:40:31+00:00

Absolute alignment requirements may never be applied to node-relative
offsets.  Andreas Herrmann spotted this flaw when a bootmem allocation on
an unaligned node was itself not aligned because the combination of an
unaligned node with an aligned offset into that node is not garuanteed to
be aligned itself.

This patch introduces two helper functions that align a node-relative
index or offset with respect to the node's starting address so that the
absolute PFN or virtual address that results from combining the two
satisfies the requested alignment.

Then all the broken ALIGN()s in alloc_bootmem_core() are replaced by these
helpers.

Signed-off-by: Johannes Weiner 
Reported-by: Andreas Herrmann 
Debugged-by: Andreas Herrmann 
Reviewed-by: Andreas Herrmann 
Tested-by: Andreas Herrmann 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: mminit_loglevel cannot be __meminitdata anymore

2008-08-20T22:40:30+00:00

mminit_loglevel is now used from mminit_verify_zonelist <- build_all_zonelists <-

1. online_pages <- memory_block_action <- memory_block_change_state <- store_mem_state (sys handler)
2. numa_zonelist_order_handler (proc handler)

so it cannot be annotated __meminit - drop it

fixes following section mismatch warning:
WARNING: vmlinux.o(.text+0x71628): Section mismatch in reference from the function mminit_verify_zonelist() to the variable .meminit.data:mminit_loglevel
The function mminit_verify_zonelist() references
the variable __meminitdata mminit_loglevel.
This is often because mminit_verify_zonelist lacks a __meminitdata
annotation or the annotation of mminit_loglevel is wrong.

Signed-off-by: Marcin Slusarz 
Acked-by: Mel Gorman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: show free swap as signed

2008-08-20T22:40:30+00:00

Adjust m show_swap_cache_info() to show "Free swap" as a
signed long: the signed format is preferable, because during swapoff
nr_swap_pages can legitimately go negative, so makes more sense thus
(it used to be shown redundantly, once as signed and once as unsigned).

Signed-off-by: Hugh Dickins 
Reviewed-by: KOSAKI Motohiro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: page_remove_rmap comments on PageAnon

2008-08-20T22:40:30+00:00

Add a comment to s390's page_test_dirty/page_clear_dirty/page_set_dirty
dance in page_remove_rmap(): I was wrong to think the PageSwapCache test
could be avoided, and would like a comment in there to remind me.  And
mention s390, to help us remember that this block is not really common.

Also move down the "It would be tidy to reset PageAnon" comment: it does
not belong to s390's block, and it would be unwise to reset PageAnon
before we're done with testing it.

Signed-off-by: Hugh Dickins 
Acked-by: Martin Schwidefsky 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6

2008-08-15T22:32:13+00:00

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6:
  security: Fix setting of PF_SUPERPRIV by __capable()

bootmem allocator: alloc_bootmem_core(): page-align the end offset

2008-08-15T15:35:41+00:00

This is the minimal sequence that jams the allocator:

void *p, *q, *r;
p = alloc_bootmem(PAGE_SIZE);
q = alloc_bootmem(64);
free_bootmem(p, PAGE_SIZE);
p = alloc_bootmem(PAGE_SIZE);
r = alloc_bootmem(64);

after this sequence (assuming that the allocator was empty or page-aligned
before), pointer "q" will be equal to pointer "r".

What's hapenning inside the allocator:
p = alloc_bootmem(PAGE_SIZE);
in allocator: last_end_off == PAGE_SIZE, bitmap contains bits 10000...
q = alloc_bootmem(64);
in allocator: last_end_off == PAGE_SIZE + 64, bitmap contains 11000...
free_bootmem(p, PAGE_SIZE);
in allocator: last_end_off == PAGE_SIZE + 64, bitmap contains 01000...
p = alloc_bootmem(PAGE_SIZE);
in allocator: last_end_off == PAGE_SIZE, bitmap contains 11000...
r = alloc_bootmem(64);

and now:

it finds bit "2", as a place where to allocate (sidx)

it hits the condition

if (bdata->last_end_off && PFN_DOWN(bdata->last_end_off) + 1 == sidx))
start_off = ALIGN(bdata->last_end_off, align);

-you can see that the condition is true, so it assigns start_off =
ALIGN(bdata->last_end_off, align); (that is PAGE_SIZE) and allocates
over already allocated block.

With the patch it tries to continue at the end of previous allocation only
if the previous allocation ended in the middle of the page.

Signed-off-by: Mikulas Patocka 
Acked-by: Johannes Weiner 
Cc: David Miller 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

security: Fix setting of PF_SUPERPRIV by __capable()

2008-08-14T12:59:43+00:00

Fix the setting of PF_SUPERPRIV by __capable() as it could corrupt the flags
the target process if that is not the current process and it is trying to
change its own flags in a different way at the same time.

__capable() is using neither atomic ops nor locking to protect t->flags.  This
patch removes __capable() and introduces has_capability() that doesn't set
PF_SUPERPRIV on the process being queried.

This patch further splits security_ptrace() in two:

 (1) security_ptrace_may_access().  This passes judgement on whether one
     process may access another only (PTRACE_MODE_ATTACH for ptrace() and
     PTRACE_MODE_READ for /proc), and takes a pointer to the child process.
     current is the parent.

 (2) security_ptrace_traceme().  This passes judgement on PTRACE_TRACEME only,
     and takes only a pointer to the parent process.  current is the child.

     In Smack and commoncap, this uses has_capability() to determine whether
     the parent will be permitted to use PTRACE_ATTACH if normal checks fail.
     This does not set PF_SUPERPRIV.

Two of the instances of __capable() actually only act on current, and so have
been changed to calls to capable().

Of the places that were using __capable():

 (1) The OOM killer calls __capable() thrice when weighing the killability of a
     process.  All of these now use has_capability().

 (2) cap_ptrace() and smack_ptrace() were using __capable() to check to see
     whether the parent was allowed to trace any process.  As mentioned above,
     these have been split.  For PTRACE_ATTACH and /proc, capable() is now
     used, and for PTRACE_TRACEME, has_capability() is used.

 (3) cap_safe_nice() only ever saw current, so now uses capable().

 (4) smack_setprocattr() rejected accesses to tasks other than current just
     after calling __capable(), so the order of these two tests have been
     switched and capable() is used instead.

 (5) In smack_file_send_sigiotask(), we need to allow privileged processes to
     receive SIGIO on files they're manipulating.

 (6) In smack_task_wait(), we let a process wait for a privileged process,
     whether or not the process doing the waiting is privileged.

I've tested this with the LTP SELinux and syscalls testscripts.

Signed-off-by: David Howells 
Acked-by: Serge Hallyn 
Acked-by: Casey Schaufler 
Acked-by: Andrew G. Morgan 
Acked-by: Al Viro 
Signed-off-by: James Morris