Messages in this thread Patch in this message | | | Date | Wed, 11 Feb 2009 15:10:27 +0100 | From | Markus Metzger <> | Subject | [patch] x86, ptrace: fix double-free on race |
| |
Ptrace_detach() races with __ptrace_unlink() if the traced task is reaped while detaching. This might cause a double-free of the BTS buffer.
Change the ptrace_detach() path to only do the memory accounting in ptrace_bts_detach() and leave the buffer free to ptrace_bts_untrace() which will be called from __ptrace_unlink().
The fix follows a proposal from Oleg Nesterov.
Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Markus Metzger <markus.t.metzger@intel.com> ---
Index: gits/arch/x86/kernel/ptrace.c =================================================================== --- gits.orig/arch/x86/kernel/ptrace.c 2009-01-22 13:09:37.000000000 +0100 +++ gits/arch/x86/kernel/ptrace.c 2009-02-11 08:55:49.000000000 +0100 @@ -810,12 +810,14 @@ static void ptrace_bts_detach(struct task_struct *child) { - if (unlikely(child->bts)) { - ds_release_bts(child->bts); - child->bts = NULL; - - ptrace_bts_free_buffer(child); - } + /* Ptrace_detach() races with ptrace_untrace() in case + * the child dies and is reaped by another thread. + * + * We only do the memory accounting at this point and + * leave the buffer deallocation and the bts tracer + * release to ptrace_bts_untrace() which will be called + * later on with tasklist_lock held. */ + release_locked_buffer(child->bts_buffer, child->bts_size); } #else static inline void ptrace_bts_fork(struct task_struct *tsk) {} Index: gits/include/linux/mm.h =================================================================== --- gits.orig/include/linux/mm.h 2009-02-11 08:40:37.000000000 +0100 +++ gits/include/linux/mm.h 2009-02-11 08:51:28.000000000 +0100 @@ -1304,5 +1304,6 @@ extern void *alloc_locked_buffer(size_t size); extern void free_locked_buffer(void *buffer, size_t size); +extern void release_locked_buffer(void *buffer, size_t size); #endif /* __KERNEL__ */ #endif /* _LINUX_MM_H */ Index: gits/mm/mlock.c =================================================================== --- gits.orig/mm/mlock.c 2009-02-11 08:40:37.000000000 +0100 +++ gits/mm/mlock.c 2009-02-11 08:49:17.000000000 +0100 @@ -660,7 +660,7 @@ return buffer; } -void free_locked_buffer(void *buffer, size_t size) +void release_locked_buffer(void *buffer, size_t size) { unsigned long pgsz = PAGE_ALIGN(size) >> PAGE_SHIFT; @@ -670,6 +670,11 @@ current->mm->locked_vm -= pgsz; up_write(¤t->mm->mmap_sem); +} + +void free_locked_buffer(void *buffer, size_t size) +{ + release_locked_buffer(buffer, size); kfree(buffer); } --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.
| |