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Revision 4ceb5db9757aaeadcf8fbbf97d76bd42aa4df0d6 authored by Linus Torvalds on 01 August 2005, 18:14:49 UTC, committed by Linus Torvalds on 01 August 2005, 18:14:49 UTC 
Fix get_user_pages() race for write access
 
There's no real guarantee that handle_mm_fault() will always be able to
break a COW situation - if an update from another thread ends up
modifying the page table some way, handle_mm_fault() may end up
requiring us to re-try the operation.

That's normally fine, but get_user_pages() ended up re-trying it as a
read, and thus a write access could in theory end up losing the dirty
bit or be done on a page that had not been properly COW'ed.

This makes get_user_pages() always retry write accesses as write
accesses by making "follow_page()" require that a writable follow has
the dirty bit set.  That simplifies the code and solves the race: if the
COW break fails for some reason, we'll just loop around and try again.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent 8d894c4
History
Tip revision: d1221cea11fca0f6946bdd032a45b22cecfc0f99 authored by Linus Torvalds on 13 September 2022, 13:11:38 UTC
Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Tip revision: d1221ce
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REPORTING-BUGS -rw-r--r-- 2.9 KB

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